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166-510: In 1967, S. B. Carter reported the use of shadow-evaporated palladium islands for cell attachment . After this first bio-MEMS study, subsequent development in the field was slow for around 20 years. In 1985, Unipath Inc. commercialized ClearBlue , a pregnancy test still used today that can be considered the first microfluidic device containing paper and the first microfluidic product to market. In 1990, Andreas Manz and H. Michael Widmer from Ciba-Geigy (now Novartis ), Switzerland first coined

332-961: A Harvard chemist, introduced inexpensive PDMS -based microfabrication and this revolutionized the bio-MEMS field. Since then, the field of bio-MEMS has exploded. Selected major technical achievements during bio-MEMS development of the 1990s include: Today, hydrogels such as agarose , biocompatible photoresists , and self-assembly are key areas of research in improving bio-MEMS as replacements or complements to PDMS . Conventional micromachining techniques such as wet etching , dry etching, deep reactive ion etching, sputtering , anodic bonding , and fusion bonding have been used in bio-MEMS to make flow channels , flow sensors , chemical detectors, separation capillaries, mixers, filters , micropumps and valves. However, there are some drawbacks to using silicon-based devices in biomedical applications such as their high cost and bioincompatibility . Due to being single-use only, larger than their MEMS counterparts, and

498-464: A chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of white light frequencies . They absorb certain portions of the visible spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation. This is what gives rise to color . The attenuation of light of all frequencies and wavelengths

664-450: A half-life of 6.5 million years (found in nature), Pd with 17 days, and Pd with 3.63 days. Eighteen other radioisotopes have been characterized with atomic weights ranging from 90.94948(64) u ( Pd) to 122.93426(64) u ( Pd). These have half-lives of less than thirty minutes, except Pd (half-life: 8.47 hours), Pd (half-life: 13.7 hours), and Pd (half-life: 21 hours). For isotopes with atomic mass unit values less than that of

830-871: A pH gradient (usually generated with electrodes ) perpendicular to the flow direction. Sorting and focusing of the species of interest is achieved because an electrophoretic force causes perpendicular migration until it flows along its respective isoelectric points. Dielectrophoresis is the motion of uncharged particles due to induced polarization from nonuniform electric fields. Dielectrophoresis can be used in bio-MEMS for dielectrophoresis traps, concentrating specific particles at specific points on surfaces, and diverting particles from one flow stream to another for dynamic concentration. Microfluidics refers to systems that manipulate small (μL, nL, pL, fL) amounts of fluids on microfabricated substrates. Microfluidic approaches to bio-MEMS confer several advantages: An interesting approach combining electrokinetic phenomena and microfluidics

996-447: A boundary at a steep angle, the light will be completely reflected. This effect, called total internal reflection , is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle , only light that enters the fiber within a certain range of angles will be propagated. This range of angles

1162-947: A central channel traps pairs of cells that are in direct contact or separated by a small gap. However, in general, the non-zero motility and short cell cycle time of stem cells often disrupt the spatial organization imposed by these microtechnologies. Embryoid bodies are a common in vitro pluripotency test for stem cells and their size needs to be controlled to induce directed differentiation to specific lineages. High throughput formation of uniform sized embryoid bodies with microwells and microfluidics allows easy retrieval and more importantly, scale up for clinical contexts. Actively controlling embryoid body cell organization and architecture can also direct stem cell differentiation using microfluidic gradients of endoderm -, mesoderm - and ectoderm -inducing factors, as well as self-renewal factors. Assisted reproductive technologies help to treat infertility and genetically improve livestock. However,

1328-586: A challenge because it is difficult to ascertain if the microneedles effectively penetrated the skin. Some drugs, such as diazepam , are poorly soluble and need to be aerosolized immediately prior to intranasal administration . Bio-MEMS technology using piezoelectric transducers to liquid reservoirs can be used in these circumstances to generate narrow size distribution of aerosols for better drug delivery. Implantable drug delivery systems have also been developed to administer therapeutic agents that have poor bioavailability or require localized release and exposure at

1494-493: A charged species in a liquid moves under the influence of an applied electric field . Electrophoresis has been used to fractionate small ions , charged organic molecules, proteins , and DNA . Electrophoresis and microfluidics are highly synergistic because it is possible to use higher voltages in microchannels due to faster heat removal . Isoelectric focusing is the separation of proteins, organelles , and cells with different isoelectric points . Isoelectric focusing requires

1660-605: A few conditions requires a large number of cells and supplies, expensive and bulky incubators , large fluid volumes (~0.1 – 2 mL per sample), and tedious human labour. The requirement of human labour also limits the number and length between time points for experiments. Microfluidic cell cultures are potentially a vast improvement because they can be automated, as well as yield lower overall cost, higher throughput, and more quantitative descriptions of single-cell behaviour variability. By including gas exchange and temperature control systems on chip, microfluidic cell culturing can eliminate

1826-427: A fiber of silica glass that confines the incident light beam to the inside. In optical fibers, the main source of attenuation is scattering from molecular level irregularities, called Rayleigh scattering , due to structural disorder and compositional fluctuations of the glass structure . This same phenomenon is seen as one of the limiting factors in the transparency of infrared missile domes. Further attenuation

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1992-505: A group of elements referred to as the platinum group metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them. More than half the supply of palladium and its congener platinum is used in catalytic converters , which convert as much as 90% of the harmful gases in automobile exhaust ( hydrocarbons , carbon monoxide , and nitrogen dioxide ) into nontoxic substances ( nitrogen , carbon dioxide and water vapor ). Palladium

2158-400: A high transmission of ultraviolet light. Thus, when a material is illuminated, individual photons of light can make the valence electrons of an atom transition to a higher electronic energy level . The photon is destroyed in the process and the absorbed radiant energy is transformed to electric potential energy. Several things can happen, then, to the absorbed energy: It may be re-emitted by

2324-465: A human operator is acceptable. Electromagnetic solenoid valves have similar actuation times compared to Quake valves, but have larger footprints and are not integrated into the device substrate. This is an issue when device dimensions are an issue, such as in implantable devices. Despite the fact that diffusion times are significantly shorter in microfluidic systems due to small length scales, there are still challenges to removing concentration gradients at

2490-441: A layer of palladium(II) oxide (PdO). It may slowly develop a slight brownish coloration over time, likely due to the formation of a surface layer of its monoxide. Palladium films with defects produced by alpha particle bombardment at low temperature exhibit superconductivity having T c = 3.2 K. Naturally occurring palladium is composed of seven isotopes , six of which are stable. The most stable radioisotopes are Pd with

2656-415: A membrane, glass, or silicon chip by metallic pins. For detection, fluorescently-labelled single strand cDNA from cells hybridize to the molecules on the microarray and a differential comparison between a treated sample (labelled red, for example) and an untreated sample (labelled in another color such as green) is used for analysis. Red dots mean that the corresponding gene was expressed at a higher level in

2822-403: A number of electrons (given by the atomic number Z in the periodic table ). Recall that all light waves are electromagnetic in origin. Thus they are affected strongly when coming into contact with negatively charged electrons in matter. When photons (individual packets of light energy) come in contact with the valence electrons of an atom, one of several things can and will occur: Most of

2988-527: A portion of the incoming light. The remaining frequencies (or wavelengths) are free to be reflected or transmitted. This is how colored glass is produced. Most liquids and aqueous solutions are highly transparent. For example, water, cooking oil, rubbing alcohol, air, and natural gas are all clear. Absence of structural defects (voids, cracks, etc.) and molecular structure of most liquids are chiefly responsible for their excellent optical transmission. The ability of liquids to "heal" internal defects via viscous flow

3154-462: A range of wavelengths. Guided light wave transmission via frequency selective waveguides involves the emerging field of fiber optics and the ability of certain glassy compositions to act as a transmission medium for a range of frequencies simultaneously ( multi-mode optical fiber ) with little or no interference between competing wavelengths or frequencies. This resonant mode of energy and data transmission via electromagnetic (light) wave propagation

3320-703: A redox electron current that is measured by a working electrode. Amperometric biosensors have been used in bio-MEMS for detection of glucose , galactose , lactose , urea , and cholesterol , as well as for applications in gas detection and DNA hybridization . In potentiometric biosensors, measurements of electric potential at one electrode are made in reference to another electrode. Examples of potentiometric biosensors include ion-sensitive field effect transistors (ISFET) , Chemical field-effect transistors (chem-FET), and light-addressable potentiometric sensors (LAPS) . In conductometric biosensors , changes in electrical impedance between two electrodes are measured as

3486-426: A regular lattice and a " sea of electrons " moving randomly between the atoms. In metals, most of these are non-bonding electrons (or free electrons) as opposed to the bonding electrons typically found in covalently bonded or ionically bonded non-metallic (insulating) solids. In a metallic bond, any potential bonding electrons can easily be lost by the atoms in a crystalline structure. The effect of this delocalization

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3652-491: A relatively low cost. These components are free of internal stress or intrinsic birefringence , and allow relatively large doping levels or optimized custom-designed doping profiles. This makes ceramic laser elements particularly important for high-energy lasers. The development of transparent panel products will have other potential advanced applications including high strength, impact-resistant materials that can be used for domestic windows and skylights. Perhaps more important

3818-616: A result of a biomolecular reaction. Conductive measurements are simple and easy to use because there is no need for a specific reference electrode, and have been used to detect biochemicals, toxins , nucleic acids , and bacterial cells . A challenge in optical detection is the need for integrating detectors and photodiodes in a miniaturized portable format on the bio-MEMS. Optical detection includes fluorescence -based techniques, chemiluminescence -based techniques, and surface plasmon resonance (SPR) . Fluorescence-based optical techniques use markers that emit light at specific wavelengths and

3984-494: A slightly radioactive long-lived fission product . Depending on end use, the radioactivity contributed by the Pd might make the recovered palladium unusable without a costly step of isotope separation . The largest use of palladium today is in catalytic converters. Palladium is also used in jewelry, dentistry , watch making, blood sugar test strips, aircraft spark plugs , surgical instruments , and electrical contacts . Palladium

4150-507: A strategic resource during World War II, many jewelry bands were made out of palladium. Palladium was little used in jewelry because of the technical difficulty of casting . With the casting problem resolved the use of palladium in jewelry increased, originally because platinum increased in price while the price of palladium decreased. In early 2004, when gold and platinum prices rose steeply, China began fabricating volumes of palladium jewelry, consuming 37 tonnes in 2005. Subsequent changes in

4316-627: A target site. Examples include a PDMS microfluidic device implanted under the conjunctiva for drug delivery to the eye to treat ocular diseases and microchips with gold-capped drug reservoirs for osteoporosis . In implantable bio-MEMS for drug delivery, it is important to consider device rupture and dose dumping , fibrous encapsulation of the device, and device explantation. Most drugs also need to be delivered in relatively large quantities (milliliters or even greater), which makes implantable bio-MEMS drug delivery challenging due to their limited drug-holding capacity. Palladium Palladium

4482-433: A trade-off between optical performance, mechanical strength and price. For example, sapphire (crystalline alumina ) is very strong, but it is expensive and lacks full transparency throughout the 3–5 μm mid-infrared range. Yttria is fully transparent from 3–5 μm, but lacks sufficient strength, hardness, and thermal shock resistance for high-performance aerospace applications. A combination of these two materials in

4648-419: A typical metal or ceramic object are in the form of grain boundaries , which separate tiny regions of crystalline order. When the size of the scattering center (or grain boundary) is reduced below the size of the wavelength of the light being scattered, the scattering no longer occurs to any significant extent. In the formation of polycrystalline materials (metals and ceramics) the size of the crystalline grains

4814-453: A uniquely high absorption capacity and does not lose its ductility until x approaches 1. This property has been investigated in designing an efficient and safe hydrogen fuel storage medium, though palladium itself is currently prohibitively expensive for this purpose. The content of hydrogen in palladium can be linked to magnetic susceptibility , which decreases with the increase of hydrogen and becomes zero for PdH 0.62 . At any higher ratio,

4980-567: A way that does not produce large forces that shear the cells off the substrate. Dispensing fluids by manual or robotic pipetting can be replaced with micropumps and microvalves, where fluid metering is straightforward to determine as opposed to continuous flow systems by micromixers. A fully automated microfluidic cell culture system has been developed to study osteogenic differentiation of human embryonic stem cells . A handheld microfluidic cell culture incubator capable of heating and pumping cell culture solutions has also been developed. Due to

5146-406: Is digital microfluidics . In digital microfluidics, a substrate surface is micropatterned with electrodes and selectively activated. Manipulation of small fluid droplets occurs via electrowetting , which is the phenomenon where an electric field changes the wettability of an electrolyte droplet on a surface. Lithographic methods for microfluidic device manufacturing are ineffective in forming

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5312-400: Is polymeric ). Drug delivery by microneedles include coating the surface with therapeutic agents, loading drugs into porous or hollow microneedles, or fabricating the microneedles with drug and coating matrix for maximum drug loading. Microneedles for interstitial fluid extraction, blood extraction, and gene delivery are also being developed. The efficiency of microneedle drug delivery remains

5478-531: Is a chemical element ; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston . He named it after the asteroid Pallas (formally 2 Pallas), which was itself named after the epithet of the Greek goddess Athena , acquired by her when she slew Pallas . Palladium, platinum , rhodium , ruthenium , iridium and osmium form

5644-652: Is a very common biological sample because it cycles through the body every few minutes and its contents can indicate many aspects of health. In blood analysis, white blood cells , platelets , bacteria , and plasma must be separated. Sieves, weirs, inertial confinement, and flow diversion devices are some approaches used in preparing blood plasma for cell-free analysis. Sieves can be microfabricated with high-aspect-ratio columns or posts, but are only suitable for low loading to avoid clogging with cells. Weirs are shallow mesa-like sections used to restrict flow to narrow slots between layers without posts. One advantage of using weirs

5810-449: Is achieved through micro- and nano-scale cantilevers for stress sensing and mass sensing, or micro- and nano-scale plates or membranes. In stress sensing, the biochemical reaction is performed selectively on one side of the cantilever to cause a change in surface free energy . This results in bending of the cantilever that is measurable either optically ( laser reflection into a four-position detector) or electrically ( piezo-resistor at

5976-479: Is affected. High doses of palladium could be poisonous; tests on rodents suggest it may be carcinogenic , though until the recent research cited above, no clear evidence indicated that the element harms humans. Like other platinum-group metals , bulk Pd is quite inert. Although contact dermatitis has been reported, data on the effects are limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it advisable to avoid

6142-399: Is also produced in nuclear fission reactors and can be extracted from spent nuclear fuel (see synthesis of precious metals ), though this source for palladium is not used. None of the existing nuclear reprocessing facilities are equipped to extract palladium from the high-level radioactive waste . A complication for the recovery of palladium in spent fuel is the presence of Pd ,

6308-492: Is also used in electronics, dentistry , medicine , hydrogen purification , chemical applications, groundwater treatment , and jewelry. Palladium is a key component of fuel cells , in which hydrogen and oxygen react to produce electricity, heat, and water. Ore deposits of palladium and other PGMs are rare. The most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering

6474-404: Is also used to make some professional transverse (concert or classical) flutes . As a commodity, palladium bullion has ISO currency codes of XPD and 964. Palladium is one of only four metals to have such codes, the others being gold , silver and platinum. Because it adsorbs hydrogen, palladium was a key component of the controversial cold fusion experiments of the late 1980s. When it

6640-477: Is an effective catalyst for carbon–fluorine bonds . Palladium catalysis is primarily employed in organic chemistry and industrial applications, although its use is growing as a tool for synthetic biology ; in 2017, effective in vivo catalytic activity of palladium nanoparticles was demonstrated in mammals to treat disease. The primary application of palladium in electronics is in multi-layer ceramic capacitors in which palladium (and palladium-silver alloy)

6806-567: Is an excellent electrocatalyst for oxidation of primary alcohols in alkaline media. Palladium is also a versatile metal for homogeneous catalysis , used in combination with a broad variety of ligands for highly selective chemical transformations. In 2010 the Nobel Prize in Chemistry was awarded "for palladium-catalyzed cross couplings in organic synthesis" to Richard F. Heck , Ei-ichi Negishi and Akira Suzuki . A 2008 study showed that palladium

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6972-460: Is an important biochemical factor to consider in differentiation via hypoxia-induced transcription factors (HIFs) and related signaling pathways, most notably in the development of blood, vasculature , placental , and bone tissues. Conventional methods of studying oxygen effects relied on setting the entire incubator at a particular oxygen concentration, which limited analysis to pair-wise comparisons between normoxic and hypoxic conditions instead of

7138-462: Is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding. Optical waveguides are used as components in integrated optical circuits (e.g., combined with lasers or light-emitting diodes , LEDs) or as the transmission medium in local and long-haul optical communication systems. Attenuation in fiber optics , also known as transmission loss ,

7304-481: Is caused by light absorbed by residual materials, such as metals or water ions, within the fiber core and inner cladding. Light leakage due to bending, splices, connectors, or other outside forces are other factors resulting in attenuation. At high optical powers, scattering can also be caused by nonlinear optical processes in the fiber. Many marine animals that float near the surface are highly transparent, giving them almost perfect camouflage . However, transparency

7470-404: Is complete, a strong, stationary magnetic field is applied to immobilize the target-bound beads and wash away unbound beads. The H-filter is a microfluidic device with two inlets and two outlets that takes advantage of laminar flow and diffusion to separate components that diffuse across the interface between two inlet streams. By controlling the flow rate, diffusion distance, and residence time of

7636-906: Is dependent on many factors, including soluble and biochemical factors, fluid shear stress , cell- ECM interactions, cell-cell interactions, as well as embryoid body formation and organization. Bio-MEMS have been used to research how to optimize the culture and growth conditions of stem cells by controlling these factors. Assaying stem cells and their differentiated progeny is done with microarrays for studying how transcription factors and miRNAs determine cell fate, how epigenetic modifications between stem cells and their daughter cells affect phenotypes , as well as measuring and sorting stem cells by their protein expression. Microfluidics can leverage its microscopic volume and laminar flow characteristics for spatiotemporal control of biochemical factors delivered to stem cells. Microfluidic gradient generators have been used to study dose-response relationships. Oxygen

7802-508: Is dependent upon the frequency of the light, the nature of the atoms in the object, and often, the nature of the electrons in the atoms of the object. Some materials allow much of the light that falls on them to be transmitted through the material without being reflected. Materials that allow the transmission of light waves through them are called optically transparent. Chemically pure (undoped) window glass and clean river or spring water are prime examples of this. Materials that do not allow

7968-416: Is determined largely by the size of the crystalline particles present in the raw material during formation (or pressing) of the object. Moreover, the size of the grain boundaries scales directly with particle size. Thus, a reduction of the original particle size well below the wavelength of visible light (about 1/15 of the light wavelength, or roughly 600 nm / 15 = 40  nm ) eliminates much of

8134-536: Is difficult for bodies made of materials that have different refractive indices from seawater. Some marine animals such as jellyfish have gelatinous bodies, composed mainly of water; their thick mesogloea is acellular and highly transparent. This conveniently makes them buoyant , but it also makes them large for their muscle mass, so they cannot swim fast, making this form of camouflage a costly trade-off with mobility. Gelatinous planktonic animals are between 50 and 90 percent transparent. A transparency of 50 percent

8300-423: Is due to the combined mechanisms of absorption and scattering . Transparency can provide almost perfect camouflage for animals able to achieve it. This is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent. With regard to the absorption of light, primary material considerations include: With regard to the scattering of light ,

8466-435: Is enough to make an animal invisible to a predator such as cod at a depth of 650 metres (2,130 ft); better transparency is required for invisibility in shallower water, where the light is brighter and predators can see better. For example, a cod can see prey that are 98 percent transparent in optimal lighting in shallow water. Therefore, sufficient transparency for camouflage is more easily achieved in deeper waters. For

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8632-529: Is finely divided, as with palladium on carbon , palladium forms a versatile catalyst ; it speeds heterogeneous catalytic processes like hydrogenation , dehydrogenation , and petroleum cracking . Palladium is also essential to the Lindlar catalyst , also called Lindlar's Palladium. A large number of carbon–carbon bonding reactions in organic chemistry are facilitated by palladium compound catalysts. For example: When dispersed on conductive materials, palladium

8798-667: Is firstly because mRNA transcripts often correlate poorly with the actual amount of protein synthesized. Secondly, DNA microarrays cannot identify post-translational modification of proteins, which directly influences protein function. Thirdly, some bodily fluids such as urine lack mRNA . A protein microarray consists of a protein library immobilized on a substrate chip, usually glass, silicon, polystyrene , PVDF , or nitrocellulose . In general, there are three types of protein microarrays: functional, analytical or capture, and reverse-phase protein arrays. Protein microarrays have stringent production, storage, and experimental conditions due to

8964-415: Is heated under controlled conditions. Prior to 2004, the principal use of palladium in jewelry was the manufacture of white gold. Palladium is one of the three most popular alloying metals in white gold ( nickel and silver can also be used). Palladium-gold is more expensive than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur). When platinum became

9130-419: Is intense local heating and shear forces . In a passive mixing element, mixing is achieved by temporal and spatial redistribution of incoming laminar flow through the use of parallel conduits of variable path length and or diameter. The net result of having a variety of parallel flow channels of varying length is that material initially at the edge of the laminar flow profile can be repeatedly redistributed to

9296-416: Is more advantageous than conventional well plates due to its higher throughput and lower requirement of expensive reagents. Cell fate is regulated by both interactions between stem cells and interactions between stem cells and membrane proteins . Manipulating cell seeding density is a common biological technique in controlling cell–cell interactions , but controlling local density is difficult and it

9462-494: Is motion at the atomic and molecular levels. The primary mode of motion in crystalline substances is vibration . Any given atom will vibrate around some mean or average position within a crystalline structure, surrounded by its nearest neighbors. This vibration in two dimensions is equivalent to the oscillation of a clock's pendulum. It swings back and forth symmetrically about some mean or average (vertical) position. Atomic and molecular vibrational frequencies may average on

9628-433: Is not very mobile in the environment and has a relatively low decay energy , Pd is usually considered to be among the less concerning of the long-lived fission products . Palladium compounds exist primarily in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element. Palladium(II) chloride

9794-566: Is often difficult to decouple effects between soluble signals in the medium and physical cell–cell interactions. Micropatterning of cell adhesion proteins can be used in defining the spatial positions of different cells on a substrate to study human ESC proliferation. Seeding stem cells into PDMS microwells and flipping them onto a substrate or another cell layer is a method of achieving precise spatial control. Gap junction communications has also been studied using microfluidics whereby negative pressure generated by fluid flow in side channels flanking

9960-405: Is one of the reasons why some fibrous materials (e.g., paper or fabric) increase their apparent transparency when wetted. The liquid fills up numerous voids making the material more structurally homogeneous. Light scattering in an ideal defect-free crystalline (non-metallic) solid that provides no scattering centers for incoming light will be due primarily to any effects of anharmonicity within

10126-411: Is prepared by reducing sodium tetrachloropalladate in the presence of dibenzylideneacetone . Palladium(0), as well as palladium(II), are catalysts in coupling reactions , as has been recognized by the 2010 Nobel Prize in Chemistry to Richard F. Heck , Ei-ichi Negishi , and Akira Suzuki . Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include

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10292-401: Is relatively lossless. An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis by the process of total internal reflection . The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The refractive index is the parameter reflecting

10458-400: Is simply to exaggerate the effect of the "sea of electrons". As a result of these electrons, most of the incoming light in metals is reflected back, which is why we see a shiny metal surface. Most insulators (or dielectric materials) are held together by ionic bonds . Thus, these materials do not have free conduction electrons , and the bonding electrons reflect only a small fraction of

10624-403: Is that the absence of posts allows more effective recycling of retentate for flow across the filter to wash off clogged cells. Magnetic beads are used to aid in analyte separation. These microscopic beads are functionalized with target molecules and moved through microfluidic channels using a varying magnetic field. This serves as a quick method of harvesting targets for analysis. After this process

10790-465: Is that walls and other applications will have improved overall strength, especially for high-shear conditions found in high seismic and wind exposures. If the expected improvements in mechanical properties bear out, the traditional limits seen on glazing areas in today's building codes could quickly become outdated if the window area actually contributes to the shear resistance of the wall. Currently available infrared transparent materials typically exhibit

10956-687: Is the dependency of the rate of wicking on environmental conditions such as temperature and relative humidity. Paper-based analytical devices are particularly attractive for point-of-care diagnostics in developing countries for both the low material cost and emphasis on colorimetric assays which allow medical professionals to easily interpret the results by eye. Compared to traditional microfluidic channels, paper microchannels are accessible for sample introduction (especially forensic -style samples such as body fluids and soil), as well as its natural filtering properties that exclude cell debris, dirt, and other impurities in samples. Paper-based replicas have demonstrated

11122-563: Is the high consumption of expensive reagents, preference for amplifying short fragments, and the production of short chimeric molecules. PCR chips serve to miniaturize the reaction environment to achieve rapid heat transfer and fast mixing due to the larger surface-to-volume ratio and short diffusion distances. The advantages of PCR chips include shorter thermal-cycling time, more uniform temperature which enhances yield, and portability for point-of-care applications. Two challenges in microfluidic PCR chips are PCR inhibition and contamination due to

11288-459: Is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon. Solutions of PdCl 2 in nitric acid react with acetic acid to give palladium(II) acetate , also a versatile reagent. PdCl 2 reacts with ligands (L) to give square planar complexes of

11454-406: Is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. It is an important factor limiting the transmission of a signal across large distances. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the very high quality of transparency of modern optical transmission media. The medium is usually

11620-461: Is the use of paper substrates in microfabrication to manipulate fluid flow for different applications. Paper microfluidics have been applied in paper electrophoresis and immunoassays , the most notable being the commercialized pregnancy test, ClearBlue. Advantages of using paper for microfluidics and electrophoresis in bio-MEMS include its low cost, biodegradability , and natural wicking action. A severe disadvantage of paper-based microfluidics

11786-543: Is to interface with the body's nervous system for recording and sending bioelectrical signals to study disease, improve prostheses , and monitor clinical parameters . Microfabrication has led to the development of Michigan probes and the Utah electrode array , which have increased electrodes per unit volume, while addressing problems of thick substrates causing damage during implantation and triggering foreign-body reaction and electrode encapsulation via silicon and metals in

11952-443: Is typically done by flow cytometry and can be implemented into microfluidics with lower fluid velocities and lower throughput than their conventional macroscopic counterparts. Microfluidic sample separation can be achieved by capillary electrophoresis or continuous-flow separation. In capillary electrophoresis, a long thin tube separates analytes by voltage as they migrate by electro-osmotic flow. For continuous-flow separation,

12118-419: Is used for electrodes. Palladium (sometimes alloyed with nickel) is or can be used for component and connector plating in consumer electronics and in soldering materials. The electronic sector consumed 33 tonnes (1.07 million troy ounces) of palladium in 2006, according to a Johnson Matthey report. Hydrogen easily diffuses through heated palladium, and membrane reactors with Pd membranes are used in

12284-574: The Heck , Suzuki , Sonogashira coupling , Stille reactions , and the Kumada coupling . Palladium(II) acetate , tetrakis(triphenylphosphine)palladium(0) (Pd(PPh 3 ) 4 ), and tris(dibenzylideneacetone)dipalladium(0) (Pd 2 (dba) 3 ) serve either as catalysts or precatalysts. Although Pd(IV) compounds are comparatively rare, one example is sodium hexachloropalladate(IV) , Na 2 [PdCl 6 ]. A few compounds of palladium(III) are also known. Palladium(VI)

12450-616: The Human Genome Project (HGP) , which started in October 1990, created demand for improvements in DNA sequencing capacity. Capillary electrophoresis thus became a focus for chemical and DNA separation. Thirdly, DARPA of the US Department of Defense supported a series of microfluidic research programs in the 1990s after realizing there was a need to develop field-deployable microsystems for

12616-955: The Norilsk–Talnakh deposits in Siberia . The other large deposit is the Merensky Reef platinum group metals deposit within the Bushveld Igneous Complex South Africa . The Stillwater igneous complex of Montana and the Roby zone ore body of the Lac des Îles igneous complex of Ontario are the two other sources of palladium in Canada and the United States. Palladium is found in the rare minerals cooperite and polarite . Many more Pd minerals are known, but all of them are very rare. Palladium

12782-794: The Transvaal Basin in South Africa; the Stillwater Complex in Montana , United States; the Sudbury Basin and Thunder Bay District of Ontario , Canada; and the Norilsk Complex in Russia. Recycling is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable investment interest. Palladium belongs to group 10 in

12948-453: The blood–brain barrier and the lungs. Organ-level lung functions have been reconstituted on lung-on-a-chip devices where a porous membrane and the seeded epithelial cell layer are cyclically stretched by applied vacuum on adjacent microchannels to mimic inhalation . The goal of stem cell engineering is to be able to control the differentiation and self-renewal of pluripotency stem cells for cell therapy . Differentiation in stem cells

13114-662: The discovery of a new noble metal in July 1802 in his lab book and named it palladium in August of the same year. He named the element after the asteroid 2 Pallas , which had been discovered two months earlier (and which was previously considered a planet ). Wollaston purified a quantity of the material and offered it, without naming the discoverer, in a small shop in Soho in April 1803. After harsh criticism from Richard Chenevix , who claimed that palladium

13280-399: The platinotype printing process, photographers make fine-art black-and-white prints using platinum or palladium salts. Often used with platinum, palladium provides an alternative to silver. Palladium is a metal with low toxicity as conventionally measured (e.g. LD 50 ). Recent research on the mechanism of palladium toxicity suggests high toxicity if measured on a longer timeframe and at

13446-411: The solid solution becomes diamagnetic . Palladium is used for purification of hydrogen on a laboratory but not industrial scale. Palladium is used in small amounts (about 0.5%) in some alloys of dental amalgam to decrease corrosion and increase the metallic lustre of the final restoration. Palladium has been used as a precious metal in jewelry since 1939 as an alternative to platinum in

13612-403: The speed of light in a material. (Refractive index is the ratio of the speed of light in vacuum to the speed of light in a given medium. The refractive index of vacuum is therefore 1.) The larger the refractive index, the more slowly light travels in that medium. Typical values for core and cladding of an optical fiber are 1.48 and 1.46, respectively. When light traveling in a dense medium hits

13778-403: The stoichiometry RPd 3 exist where R is scandium , yttrium , or any of the lanthanides . As overall mine production of palladium reached 210,000 kilograms in 2022, Russia was the top producer with 88,000 kilograms, followed by South Africa, Canada, the U.S., and Zimbabwe. Russia's company Norilsk Nickel ranks first among the largest palladium producers globally, accounting for 39% of

13944-567: The $ 900 per ounce mark. In 2016 however palladium cost around $ 614 per ounce as Russia managed to maintain stable supplies. In January 2019 palladium futures climbed past $ 1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry. Palladium reached $ 2,024.64 per troy ounce ($ 65.094/g) on 6 January 2020, passing $ 2,000 per troy ounce the first time. The price rose above $ 3,000 per troy ounce in May 2021 and March 2022. Transparency and translucency In

14110-731: The SPOT technique (stepwise synthesis of peptides on cellulose) or photolithography to make peptides. The polymerase chain reaction (PCR) is a fundamental molecular biology technique that enables the selective amplification of DNA sequences, which is useful for expanded use of rare samples e.g.: stem cells, biopsies, circulating tumor cells. The reaction involves thermal cycling of the DNA sequence and DNA polymerase through three different temperatures. Heating up and cooling down in conventional PCR devices are time-consuming and typical PCR reactions can take hours to complete. Other drawbacks of conventional PCR

14276-425: The alloy. Fountain pen nibs made from gold are sometimes plated with palladium when a silver (rather than gold) appearance is desired. Sheaffer has used palladium plating for decades, either as an accent on otherwise gold nibs or covering the gold completely. Palladium is also used by the luxury brand Hermès as one of the metals plating the hardware on their handbags, most famous of which being Birkin. In

14442-496: The alloys called " white gold ", where the naturally white color of palladium does not require rhodium plating . Palladium, being much less dense than platinum, is similar to gold in that it can be beaten into leaf as thin as 100 nm ( 1 ⁄ 250,000  in). Unlike platinum, palladium may discolor at temperatures above 400 °C (752 °F) due to oxidation, making it more brittle and thus less suitable for use in jewelry; to prevent this, palladium intended for jewelry

14608-465: The bedside or at the point-of-care is important in health care, especially in developing countries where access to centralized hospitals is limited and prohibitively expensive. To this end, point-of-care diagnostic bio-MEMS have been developed to take saliva, blood, or urine samples and in an integrated approach perform sample preconditioning, sample fractionation, signal amplification, analyte detection, data analysis, and result display. In particular, blood

14774-470: The cantilever has also been found to change the Young's modulus of the cantilever. Changing cantilever stiffness will also change its resonant frequency, and thus the noise in the oscillation signal must be analyzed to determine whether the resonant frequency is also a function of changing elasticity. One common use for this technique is in detecting nucleotide mismatches in DNA because the variation in mass caused by

14940-564: The cantilever, without submerging the cantilever, minimally impacting its oscillation. This technology is in its infancy, however, and it is still not able to be used beyond a few, limited applications. The advantage of using cantilever sensors is that there is no need for an optically detectable label on the analyte or bioreceptors. Electrical and electrochemical detection are easily adapted for portability and miniaturization , especially in comparison to optical detection. In amperometric biosensors, an enzyme -catalyzed redox reaction causes

15106-496: The cellular level in the liver and kidney. Mitochondria appear to have a key role in palladium toxicity via mitochondrial membrane potential collapse and depletion of the cellular glutathione (GSH) level. Until that recent work, it had been thought that palladium was poorly absorbed by the human body when ingested . Plants such as the water hyacinth are killed by low levels of palladium salts, but most other plants tolerate it, although tests show that, at levels above 0.0003%, growth

15272-553: The channels of microfluidic devices to isolate various types of CTCs based on their specificities (Fan et al., 2013). Other notable advancements include the creation of nano-Velcro surfaces by Hsian-Rong Tseng's team at UCLA, designed to enhance cell capture efficiency through nanostructured polymer fiber meshes (Tseng et al., 2012), and the development of sinusoidal channels by Steven A. Soper 's group at UNC Chapel Hill , which improves cell capture via geometrical modifications (Soper et al., 2011). These innovations collectively enhance

15438-482: The coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. Pd versus Ag correlations observed in bodies, which have been melted since accretion of the Solar System , must reflect the presence of short-lived nuclides in the early Solar System. Pd is also produced as a fission product in spontaneous or induced fission of U . As it

15604-1037: The desired concentration-dependent characterization. Developed solutions include the use of continuous axial oxygen gradients and arrays of microfluidic cell culture chambers separated by thin PDMS membranes to gas-filled microchannels . Fluid shear stress is relevant in the stem cell differentiation of cardiovascular lineages as well as late embryogenesis and organogenesis such as left-right asymmetry during development. Macro-scale studies do not allow quantitative analysis of shear stress to differentiation because they are performed using parallel-plate flow chambers or rotating cone apparatuses in on-off scenarios only. Poiseuille flow in microfluidics allows shear stresses to be varied systematically using channel geometry and flow rate via micropumps , as demonstrated by using arrays of perfusion chambers for mesenchymal stem cells and fibroblast cell adhesion studies. Cell- ECM interactions induce changes in differentiation and self-renewal by

15770-530: The detection of chemical and biological agents that were potential military and terrorist threats . Researchers started to use photolithography equipment for microfabrication of microelectromechanical systems (MEMS) as inherited from the microelectronics industry. At the time, the application of MEMS to biology was limited because this technology was optimized for silicon or glass wafers and used solvent-based photoresists that were not compatible with biological material. In 1993, George M. Whitesides ,

15936-832: The development of cell-based arrays , microarrays , microfabrication based tissue engineering , and artificial organs . Biological micropatterning can be used for high-throughput single cell analysis, precise control of cellular microenvironment, as well as controlled integration of cells into appropriate multi-cellular architectures to recapitulate in vivo conditions. Photolithography , microcontact printing , selective microfluidic delivery, and self-assembled monolayers are some methods used to pattern biological molecules onto surfaces. Cell micropatterning can be done using microcontact patterning of extracellular matrix proteins, cellular electrophoresis , optical tweezer arrays, dielectrophoresis , and electrochemically active surfaces. Paper microfluidics (sometimes called lab on paper)

16102-509: The development of a cardiac patch that adheres to the curvilinear surface of the heart by surface tension alone for measuring cardiac electrophysiology , and electronic tattoos for measuring skin temperature and bioelectricity . Wireless recording of electrophysiological signals is possible through addition of a piezocrystal to a circuit of two recording electrodes and a single transistor on an implanted micro-device. An external transducer emits pulses of ultrasonic energy} which impinge on

16268-707: The efficiency of these technologies in cryopreservation and the in vitro production of mammalian embryos is low. Microfluidics have been applied in these technologies to better mimic the in vivo microenvironment with patterned topographic and biochemical surfaces for controlled spatiotemporal cell adhesion, as well as minimization of dead volumes. Micropumps and microvalves can automate tedious fluid-dispensing procedures and various sensors can be integrated for real-time quality control . Bio-MEMS devices have been developed to evaluate sperm motility , perform sperm selection, as well as prevent polyspermy in in-vitro fertilization . The goal of implantable microelectrodes

16434-548: The electrodes. Michigan probes have been used in large-scale recordings and network analysis of neuronal assemblies, and the Utah electrode array has been used as a brain–computer interface for the paralyzed. Extracellular microelectrodes have been patterned onto an inflatable helix-shaped plastic in cochlear implants to improve deeper insertion and better electrode-tissue contact for transduction of high-fidelity sounds. Integrating microelectronics onto thin, flexible substrates has led to

16600-472: The electron as radiant energy (in this case, the overall effect is in fact a scattering of light), dissipated to the rest of the material (i.e., transformed into heat ), or the electron can be freed from the atom (as in the photoelectric effects and Compton effects ). The primary physical mechanism for storing mechanical energy of motion in condensed matter is through heat , or thermal energy . Thermal energy manifests itself as energy of motion. Thus, heat

16766-476: The emerging chemical processing methods encompassed by the methods of sol-gel chemistry and nanotechnology . Transparent ceramics have created interest in their applications for high energy lasers, transparent armor windows, nose cones for heat seeking missiles, radiation detectors for non-destructive testing, high energy physics, space exploration, security and medical imaging applications. Large laser elements made from transparent ceramics can be produced at

16932-500: The field of optics , transparency (also called pellucidity or diaphaneity ) is the physical property of allowing light to pass through the material without appreciable scattering of light . On a macroscopic scale (one in which the dimensions are much larger than the wavelengths of the photons in question), the photons can be said to follow Snell's law . Translucency (also called translucence or translucidity ) allows light to pass through but does not necessarily (again, on

17098-415: The fixed edge of the cantilever) due to a change in surface stress. In mass sensing, the cantilever vibrates at its resonant frequency as measured electrically or optically. When a biochemical reaction takes place and is captured on the cantilever, the mass of the cantilever changes, as does the resonant frequency. Analysis of this data can be slightly less straightforward, however, as adsorption of sample to

17264-414: The fluid in the filter, cells are excluded from the filtrate by virtue of their slower diffusion rate. The H-filter does not clog and can run indefinitely, but analytes are diluted by a factor of two. For cell analysis, cells can be studied intact or after lysis . A lytic buffer stream can be introduced alongside a stream containing cells and by diffusion induces lysis prior to further analysis. Cell analysis

17430-561: The form of the yttrium aluminium garnet (YAG) is one of the top performers in the field. When light strikes an object, it usually has not just a single frequency (or wavelength) but many. Objects have a tendency to selectively absorb, reflect, or transmit light of certain frequencies. That is, one object might reflect green light while absorbing all other frequencies of visible light. Another object might selectively transmit blue light while absorbing all other frequencies of visible light. The manner in which visible light interacts with an object

17596-411: The frequency of the incoming light wave is at or near the energy levels of the electrons within the atoms that compose the substance. In this case, the electrons will absorb the energy of the light wave and increase their energy state, often moving outward from the nucleus of the atom into an outer shell or orbital . The atoms that bind together to make the molecules of any particular substance contain

17762-410: The frequency of the light wave and the physical dimension of the scattering center. For example, since visible light has a wavelength scale on the order of a micrometre, scattering centers will have dimensions on a similar spatial scale. Primary scattering centers in polycrystalline materials include microstructural defects such as pores and grain boundaries. In addition to pores, most of the interfaces in

17928-535: The general idea is to apply a field at an angle to the flow direction to deflect the sample flow path toward different channels. Examples of continuous-flow separation techniques include continuous-flow electrophoresis, isoelectric focusing , continuous-flow magnetic separations, and molecular sieving . The work of Z. Hugh Fan and his team at the University of Florida involves the use of ligand-binding nucleic acid sequences known as aptamers , which are attached to

18094-731: The heaviest element having only one incomplete electron shell , with all shells above it empty. Palladium has the appearance of a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated nitric acid , in hot, concentrated sulfuric acid , and when finely ground, in hydrochloric acid . It dissolves readily at room temperature in aqua regia . Palladium does not react with oxygen at standard temperature (and thus does not tarnish in air ). Palladium heated to 800 °C will produce

18260-407: The incident wave. The remaining frequencies (or wavelengths) are free to propagate (or be transmitted). This class of materials includes all ceramics and glasses . If a dielectric material does not include light-absorbent additive molecules (pigments, dyes, colorants), it is usually transparent to the spectrum of visible light. Color centers (or dye molecules, or " dopants ") in a dielectric absorb

18426-771: The involved aspects. When light encounters a material, it can interact with it in several different ways. These interactions depend on the wavelength of the light and the nature of the material. Photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as plate glass and clean water , transmit much of the light that falls on them and reflect little of it; such materials are called optically transparent. Many liquids and aqueous solutions are highly transparent. Absence of structural defects (voids, cracks, etc.) and molecular structure of most liquids are mostly responsible for excellent optical transmission. Materials that do not transmit light are called opaque . Many such substances have

18592-838: The issue of collection and detection by performing microfluidic culture on an array of photoconductors which can be optoelectrically activated to manipulate cells across the chip. This platform has been adopted by Amgen and Novartis for cell line development in the biopharmaceutical industry. Micropatterned co-cultures have also contributed to bio-MEMS for tissue engineering to recapitulate in vivo conditions and 3D natural structure. Specifically, hepatocytes have been patterned to co-culture at specific cell densities with fibroblasts to maintain liver -specific functions such as albumin secretion, urea synthesis, and p450 detoxification. Similarly, integrating microfluidics with micropatterned co-cultures has enabled modelling of organs where multiple vascularized tissues interface, such as

18758-430: The lab of Stephen Quake at Stanford University . The basic scheme involves two perpendicular flow conduits separated by an impermeable elastomeric membrane at their intersection. Controlled air flow passes through one conduit while the process fluid passes through the other. A pressure gradient between the two conduits, which is tuned by changing the control air flow rate, causes the membrane to deform and obstruct flow in

18924-450: The large surface-to-volume ratio increasing surface-reagent interactions. For example, silicon substrates have good thermal conductivity for rapid heating and cooling, but can poison the polymerase reaction. Silicon substrates are also opaque, prohibiting optical detection for qPCR, and electrically conductive, preventing electrophoretic transport through the channels. Meanwhile, glass is an ideal material for electrophoresis but also inhibits

19090-510: The light scattering, resulting in a translucent or even transparent material. Computer modeling of light transmission through translucent ceramic alumina has shown that microscopic pores trapped near grain boundaries act as primary scattering centers. The volume fraction of porosity had to be reduced below 1% for high-quality optical transmission (99.99 percent of theoretical density). This goal has been readily accomplished and amply demonstrated in laboratories and research facilities worldwide using

19256-441: The low stability and necessity of considering the native folding on the immobilized proteins. Peptides, on the other hand, are more chemically resistant and can retain partial aspects of protein function. As such, peptide microarrays have been used to complement protein microarrays in proteomics research and diagnostics. Protein microarrays usually use Escherichia coli to produce proteins of interest; whereas peptide microarrays use

19422-401: The macroscopic scale) follow Snell's law; the photons can be scattered at either of the two interfaces, or internally, where there is a change in the index of refraction . In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction. Transparent materials appear clear, with

19588-440: The material (e.g., the grain boundaries of a polycrystalline material or the cell or fiber boundaries of an organic material), and by its surface, if it is rough. Diffuse reflection is typically characterized by omni-directional reflection angles. Most of the objects visible to the naked eye are identified via diffuse reflection. Another term commonly used for this type of reflection is "light scattering". Light scattering from

19754-413: The material and re-emitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. An object may be not transparent either because it reflects the incoming light or because it absorbs the incoming light. Almost all solids reflect a part and absorb a part of the incoming light. When light falls onto a block of metal , it encounters atoms that are tightly packed in

19920-1045: The microarray consists of an ordered collection of microspots each containing a single defined molecular species that interacts with the analyte for simultaneous testing of thousands of parameters in a single experiment. Some applications of genomic and proteomic microarrays are neonatal screening , identifying disease risk, and predicting therapy efficacy for personalized medicine . Oligonucleotide chips are microarrays of oligonucleotides . They can be used for detection of mutations and expression monitoring, and gene discovery and mapping. The main methods for creating an oligonucleotide microarray are by gel pads ( Motorola ), microelectrodes (Nanogen), photolithography ( Affymetrix ), and inkjet technology ( Agilent ). cDNA microarrays are often used for large-scale screening and expression studies. In cDNA microarrays, mRNA from cells are collected and converted into cDNA by reverse transcription. Subsequently, cDNA molecules (each corresponding to one gene) are immobilized as ~100 μm diameter spots on

20086-492: The most abundant stable isotope, Pd, the primary decay mode is electron capture with the primary decay product being rhodium. The primary mode of decay for those isotopes of Pd with atomic mass greater than 106 is beta decay with the primary product of this decay being silver . Radiogenic Ag is a decay product of Pd and was first discovered in 1978 in the Santa Clara meteorite of 1976. The discoverers suggest that

20252-406: The most critical factor is the length scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include: Diffuse reflection - Generally, when light strikes the surface of a (non-metallic and non-glassy) solid material, it bounces off in all directions due to multiple reflections by the microscopic irregularities inside

20418-474: The need for incubators and tissue culture hoods . However, this type of continuous microfluidic cell culture operation presents its own unique challenges as well. Flow control is important when seeding cells into microchannels because flow needs to be stopped after the initial injection of cell suspension for cells to attach or become trapped in microwells, dielectrophoretic traps, micromagnetic traps, or hydrodynamic traps . Subsequently, flow needs to be resumed in

20584-722: The operation. Micromachined surgical tools such as tiny forceps , microneedle arrays and tissue debriders have been made possible by metal and ceramic layer-by-layer microfabrication techniques for minimally invasive surgery and robotic surgery . Incorporation of sensors onto surgical tools also allows tactile feedback for the surgeon, identification of tissue type via strain and density during cutting operations, and diagnostic catheterization to measure blood flows , pressures, temperatures , oxygen content, and chemical concentrations. Microneedles, formulation systems, and implantable systems are bio-MEMS applicable to drug delivery . Microneedles of approximately 100μm can penetrate

20750-720: The opposite edge, thus drastically shortening the characteristic diffusion length scale. Biosensors are devices that consist of a biological recognition system, called the bioreceptor, and a transducer . The interaction of the analyte with the bioreceptor causes an effect that the transducer can convert into a measurement, such as an electrical signal . The most common bioreceptors used in biosensing are based on antibody–antigen interactions, nucleic acid interactions, enzymatic interactions, cellular interactions, and interactions using biomimetic materials . Common transducer techniques include mechanical detection, electrical detection, and optical detection. Mechanical detection in bio-MEMS

20916-443: The order of 0.5  μm . Scattering centers (or particles) as small as 1 μm have been observed directly in the light microscope (e.g., Brownian motion ). Optical transparency in polycrystalline materials is limited by the amount of light scattered by their microstructural features. Light scattering depends on the wavelength of the light. Limits to spatial scales of visibility (using white light) therefore arise, depending on

21082-460: The order of 10 cycles per second ( Terahertz radiation ). When a light wave of a given frequency strikes a material with particles having the same or (resonant) vibrational frequencies, those particles will absorb the energy of the light wave and transform it into thermal energy of vibrational motion. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of

21248-430: The ordered lattice. Light transmission will be highly directional due to the typical anisotropy of crystalline substances, which includes their symmetry group and Bravais lattice . For example, the seven different crystalline forms of quartz silica ( silicon dioxide , SiO 2 ) are all clear, transparent materials . Optically transparent materials focus on the response of a material to incoming light waves of

21414-506: The ore in aqua regia , neutralizing the solution with sodium hydroxide , and precipitating platinum as ammonium chloroplatinate with ammonium chloride . He added mercuric cyanide to form the compound palladium(II) cyanide , which was heated to extract palladium metal. Palladium chloride was at one time prescribed as a tuberculosis treatment at the rate of 0.065 g per day (approximately one milligram per kilogram of body weight). This treatment had many negative side-effects , and

21580-430: The overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. The opposite property of translucency is opacity . Other categories of visual appearance, related to the perception of regular or diffuse reflection and transmission of light, have been organized under the concept of cesia in an order system with three variables, including transparency, translucency and opacity among

21746-455: The periodic table, but the configuration in the outermost electrons is in accordance with Hund's rule . Electrons that by the Madelung rule would be expected to occupy the 5 s instead fill the 4 d  orbitals , as it is more energetically favorable to have a completely filled 4d shell instead of the 5s 4d configuration. This 5s configuration, unique in period 5 , makes palladium

21912-499: The piezocrystal, and extracellular voltage changes are backscattered ultrasonically by the piezocrystal, allowing for measurement. A network of so-called "neural dust" motes can map signals throughout a region of the body where the micro-sensors are implanted. Bio-MEMS for surgical applications can improve existing functionality, add new capabilities for surgeons to develop new techniques and procedures, and improve surgical outcomes by lowering risk and providing real-time feedback during

22078-449: The plug. Because of the limited temperature difference that TE units can provide, multiple are often chained in series to produce subzero temperatures at the substrate-fluid interface, allowing for more rapid cooling. Current state of the art ice valve technology features short closing times (0.37 s at 10 μL/min) and also operates at high flow rates (1150 μL/min). Ice valves were first introduced in 1995 where pressurized liquid carbon dioxide

22244-453: The presence of an incorrect base is enough to change the resonant frequency of the cantilever and register a signal. Mass sensing is not as effective in fluids because the minimum detectable mass is much higher in damped mediums . Suspended microchannel resistors are a special type of cantilever design that are able to work around this limitation using microfluidic channels inside the cantilever. These channels can move in situ samples around on

22410-488: The presence or enhancement/reduction (e.g. fluorescence resonance energy transfer ) in optical signal indicates a reaction has occurred. Fluorescence-based detection has been used in microarrays and PCR on a chip devices. Chemiluminescence is light generation by energy release from a chemical reaction. Bioluminescence and electrochemiluminescence are subtypes of chemiluminescence. Surface plasmon resonance sensors can be thin-film refractometers or gratings that measure

22576-550: The price to an all-time high of $ 1,340 per troy ounce ($ 43/ g ) in January 2001. Around that time, the Ford Motor Company , fearing that automobile production would be disrupted by a palladium shortage, stockpiled the metal. When prices fell in early 2001, Ford lost nearly US$ 1 billion. World demand for palladium increased from 100 tons in 1990 to nearly 300 tons in 2000. The global production of palladium from mines

22742-401: The process channel. In MSL, the channels for both the process fluid and the control fluid are cast out of an elastomeric mold, making it an entirely additive manufacturing process. Ice valves operate by transporting heat away from a single portion of a flow channel, causing the fluid to solidify and stop flow through that region. Thermoelectric (TE) units are used to transport heat away from

22908-439: The production of high purity hydrogen. Palladium is used in palladium-hydrogen electrodes in electrochemical studies. Palladium(II) chloride readily catalyzes carbon monoxide gas to carbon dioxide and is useful in carbon monoxide detectors . Palladium readily adsorbs hydrogen at room temperatures, forming palladium hydride PdH x with x less than 1. While this property is common to many transition metals, palladium has

23074-434: The reaction. Polymers, particularly PDMS , are optically transparent, not inhibitory, and can be used to coat an electrophoretic glass channel. Various other surface treatments also exist, including polyethylene glycol, bovine serum albumin, and silicon dioxide. There are stationary (chamber-based), dynamic (continuous flow-based), and microdroplet ( digital PCR ) chip architectures. The ability to perform medical diagnosis at

23240-541: The relative price of platinum lowered demand for palladium to 17.4 tonnes in 2009. Demand for palladium as a catalyst has increased the price of palladium to about 50% higher than that of platinum in January 2019. In January 2010, hallmarks for palladium were introduced by assay offices in the United Kingdom, and hallmarking became mandatory for all jewelry advertising pure or alloyed palladium. Articles can be marked as 500, 950, or 999 parts of palladium per thousand of

23406-980: The requirement of clean room facilities, high material and processing costs make silicon -based bio-MEMS less economically attractive. In vivo , silicon-based bio-MEMS can be readily functionalized to minimize protein adsorption , but the brittleness of silicon remains a major issue. Using plastics and polymers in bio-MEMS is attractive because they can be easily fabricated, compatible with micromachining and rapid prototyping methods, as well as have low cost. Many polymers are also optically transparent and can be integrated into systems that use optical detection techniques such as fluorescence , UV/Vis absorbance , or Raman method . Moreover, many polymers are biologically compatible , chemically inert to solvents , and electrically insulating for applications where strong electrical fields are necessary such as electrophoretic separation . Surface chemistry of polymers can also be modified for specific applications. Specifically,

23572-641: The resonance behaviour of surface plasmon on metal or dielectric surfaces. The resonance changes when biomolecules are captured or adsorbed on the sensor surface and depends on the concentration of the analyte as well as its properties. Surface plasmon resonance has been used in food quality and safety analysis , medical diagnostics , and environmental monitoring . The goals of genomic and proteomic microarrays are to make high-throughput genome analysis faster and cheaper, as well as identify activated genes and their sequences. There are many different types of biological entities used in microarrays, but in general

23738-720: The same effectiveness in performing common microfluidic operations such as hydrodynamic focusing , size-based molecular extraction, micro-mixing , and dilution; the common 96- and 384-well microplates for automated liquid handling and analysis have been reproduced through photolithography on paper to achieve a slimmer profile and lower material cost while maintaining compatibility with conventional microplate readers. Techniques for micropatterning paper include photolithography , laser cutting , ink jet printing, plasma treatment , and wax patterning. Electrokinetics have been exploited in bio-MEMS for separating mixtures of molecules and cells using electrical fields. In electrophoresis ,

23904-420: The screw-type mechanisms used in macroscale valves. Therefore, microfluidic devices require alternative flow control techniques, a number of which are currently popular: One inexpensive method of producing valves with fast actuation times and variable flow restriction is multilayer soft lithography (MSL). Valves produced through this fabrication technique are called Quake valves, because they were first created in

24070-403: The sensitivity and specificity of CTC detection, providing valuable tools for cancer prognosis and treatment. Conventional cell culture technology is unable to efficiently allow combinatorial testing of drug candidates, growth factors , neuropeptides , genes, and retroviruses in cell culture medium. Due to the need for cells to be fed periodically with fresh medium and passaged, even testing

24236-410: The skin barrier and deliver drugs to the underlying cells and interstitial fluid with reduced tissue damage, reduced pain, and no bleeding. Microneedles can also be integrated with microfluidics for automated drug loading or multiplexing. From the user standpoint, microneedles can be incorporated into a patch format for self-administration, and do not constitute a sharp waste biohazard (if the material

24402-407: The spectrum) of infrared light. Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural resonant frequencies of vibration of the objects. When infrared light of these frequencies strikes an object, the energy is reflected or transmitted. If the object is transparent, then the light waves are passed on to neighboring atoms through the bulk of

24568-829: The stiffness of the substrate via mechanotransduction , and different integrins interacting with ECM molecules. Micropatterning of ECM proteins by micro-contact printing , inkjet printing , and mask spraying have been used in stem cell - ECM interaction studies. It has been found by using micro-contact printing to control cell attachment area that that switch in osteogenic / adipogenic lineage in human mesenchymal stem cells can be cell shape dependent. Microfabrication of microposts and measurement of their deflection can determine traction forces exerted on cells. Photolithography can also be used to cross-link cell-seeded photo-polymerizable ECM for three-dimensional studies. Using ECM microarrays to optimize combinatorial effects of collagen , laminin , and fibronectin on stem cells

24734-420: The surface of PDMSs can be ion-irradiated with elements such as magnesium , tantalum , and iron to decrease surface hydrophobicity , allowing for better cell adhesion in in vivo applications. The most common polymers used in bio-MEMS include PMMA , PDMS , OSTEmer and SU-8 . Microscale manipulation and patterning of biological materials such as proteins , cells and tissues have been used in

24900-407: The surfaces of objects is our primary mechanism of physical observation. Light scattering in liquids and solids depends on the wavelength of the light being scattered. Limits to spatial scales of visibility (using white light) therefore arise, depending on the frequency of the light wave and the physical dimension (or spatial scale) of the scattering center. Visible light has a wavelength scale on

25066-436: The term micro total analysis system (μTAS) in their seminal paper proposing the use of miniaturized total chemical analysis systems for chemical sensing. There have been three major motivating factors behind the concept of μTAS. Firstly, drug discovery in the last decades leading up to the 1990s had been limited due to the time and cost of running many chromatographic analyses in parallel on macroscopic equipment. Secondly,

25232-456: The time scales required for microfluidic technologies. Sonication is often employed to provide local mixing of streams through the generation of ultra-high energy acoustics. Microfluidic chips utilizing sonication mixing can have both integrated and externally located ultrasonic transducers. Sonication is also used widely for cell lysis and homogenization in both macro and microfluidic systems. The primary mechanism of cell lysis by sonication

25398-583: The time, it is a combination of the above that happens to the light that hits an object. The states in different materials vary in the range of energy that they can absorb. Most glasses, for example, block ultraviolet (UV) light. What happens is the electrons in the glass absorb the energy of the photons in the UV range while ignoring the weaker energy of photons in the visible light spectrum. But there are also existing special glass types, like special types of borosilicate glass or quartz that are UV-permeable and thus allow

25564-469: The transmission of any light wave frequencies are called opaque . Such substances may have a chemical composition which includes what are referred to as absorption centers. Most materials are composed of materials that are selective in their absorption of light frequencies. Thus they absorb only certain portions of the visible spectrum. The frequencies of the spectrum which are not absorbed are either reflected back or transmitted for our physical observation. In

25730-429: The treated sample. Conversely, green dots mean that the corresponding gene was expressed at a higher level in the untreated sample. Yellow dots, as a result of the overlap between red and green dots, mean that the corresponding gene was expressed at relatively the same level in both samples, whereas dark spots indicate no or negligible expression in either sample. The motivation for using peptide and protein microarrays

25896-531: The type PdCl 2 L 2 . One example of such complexes is the benzonitrile derivative PdCl 2 (PhCN) 2 . The complex bis(triphenylphosphine)palladium(II) dichloride is a useful catalyst. Palladium forms a range of zerovalent complexes with the formula PdL 4 , PdL 3 and PdL 2 . For example, reduction of a mixture of PdCl 2 (PPh 3 ) 2 and PPh 3 gives tetrakis(triphenylphosphine)palladium(0) : Another major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0) (Pd 2 (dba) 3 ),

26062-467: The uptake of palladium is estimated to be less than 15 μg per person per day. People working with palladium or its compounds might have a considerably greater uptake. For soluble compounds such as palladium chloride , 99% is eliminated from the body within three days. The median lethal dose (LD 50 ) of soluble palladium compounds in mice is 200 mg/kg for oral and 5 mg/kg for intravenous administration . William Hyde Wollaston noted

26228-404: The use of dental alloys containing palladium on those so allergic. Some palladium is emitted with the exhaust gases of cars with catalytic converters . Between 4 and 108 ng/km of palladium particulate is released by such cars, while the total uptake from food is estimated to be less than 2 μg per person a day. The second possible source of palladium is dental restoration, from which

26394-535: The visible portion of the spectrum, this is what gives rise to color. Absorption centers are largely responsible for the appearance of specific wavelengths of visible light all around us. Moving from longer (0.7 μm) to shorter (0.4 μm) wavelengths: Red, orange, yellow, green, and blue (ROYGB) can all be identified by our senses in the appearance of color by the selective absorption of specific light wave frequencies (or wavelengths). Mechanisms of selective light wave absorption include: In electronic absorption,

26560-437: The volume reduction in microfluidic cultures, the collected concentrations are higher for better signal-to-noise ratio measurements, but collection and detection is correspondingly more difficult. In situ microscopy assays with microfluidic cell cultures may help in this regard, but have inherently lower throughput due to the microscope probe having only a small field of view. The Berkeley Lights Beacon platform has resolved

26726-460: The world's production. Palladium can be found as a free metal alloyed with gold and other platinum-group metals in placer deposits of the Ural Mountains , Australia , Ethiopia , North and South America . For the production of palladium, these deposits play only a minor role. The most important commercial sources are nickel - copper deposits found in the Sudbury Basin , Ontario , and

26892-566: Was 222  tonnes in 2006 according to the United States Geological Survey . Many were concerned about a steady supply of palladium in the wake of Russia's annexation of Crimea , partly as sanctions could hamper Russian palladium exports; any restrictions on Russian palladium exports could have exacerbated what was already expected to be a large palladium deficit in 2014. Those concerns pushed palladium prices to their highest level since 2001. In September 2014 they soared above

27058-545: Was an alloy of platinum and mercury, Wollaston anonymously offered a reward of £20 for 20 grains of synthetic palladium alloy . Chenevix received the Copley Medal in 1803 after he published his experiments on palladium. Wollaston published the discovery of rhodium in 1804 and mentions some of his work on palladium. He disclosed that he was the discoverer of palladium in a publication in 1805. Wollaston found palladium in crude platinum ore from South America by dissolving

27224-448: Was claimed in 2002, but subsequently disproven. Mixed valence palladium complexes exist, e.g. Pd 4 (CO) 4 (OAc) 4 Pd(acac) 2 forms an infinite Pd chain structure, with alternatively interconnected Pd 4 (CO) 4 (OAc) 4 and Pd(acac) 2 units. When alloyed with a more electropositive element, palladium can acquire a negative charge. Such compounds are known as palladides, such as gallium palladide . Palladides with

27390-490: Was later replaced by more effective drugs. Most palladium is used for catalytic converters in the automobile industry. Catalytic converters are targets for thieves because they contain palladium and other rare metals. In the run up to year 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted; for political reasons, the export quota was not granted on time. The ensuing market panic drove

27556-412: Was used as the cooling agent. Prefabricated mechanical screw valves and solenoid valves require no advanced microfabrication processes and are easy to implement in soft substrate materials like PDMS . Screw valves, unlike Quake and ice valves, maintain their level of flow restriction without power input, and are thus ideal for situations where the valve position may remain mostly constant and actuation by

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