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Diabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes. Proactive treatment options remain limited, largely due to a lack of sensitive and convenient diagnostics, especially early in disease progression or specifically for small fiber neuropathy (SFN), the dying back of distal small diameter nerves. Here, we report on the design, testing, and validation of a novel medical diagnostic device for the functional assessment of small fiber nerves: an electrically conductive needle array designed to record nerve activity signals in the skin and transdermal tissues, which we call the DEN (Detecting Early Neuropathy). DEN recordings were validated across a time course of high fat diet-induced DPN in mice. Based on preclinical mouse data, the device was then adapted to obtain recordings in human tissue. DEN recordings successfully recorded various types of neural activity. New functional diagnostic tools like DEN offer a promising outlook for patients needing an earlier and more sensitive diagnosis of SFN/DPN, which will allow for earlier and more effective treatment options such as implementation of glucose regulation strategies.

Rapid fluid mixing in microchannels has been a perennial quest in microfluidics for over 30 years. Presented here is an ultrafast MEMS-based mixer predicated on a rotating turbine. The turbine is capable of 30k rpm with mixing speeds of $ . The mixer is well suited to any application requiring high speed fluidic mixing but is ideally suited to the study and control of fast sequential chemical reactions, or the synthesis of kinetically controlled, metastable compounds [1]. Here, the preliminary MEMS mixer design, fabrication, and characterization are presented. To demonstrate the utility of the MEMS mixer, stable monodispersed silver nanoparticles, 1.1nm-8.0nm in diameter were synthesized using Ag(NO 3 ) and NaBH 4 to quickly nucleate the nanoparticles. Ligand capping at precision controlled times, 1ms to several seconds after initial nucleation with borohydride, quenched the reaction and produced nanoparticles of controlled diameters and dispersity.

Microfabricated needle arrays for minimally invasive bioassay and drug delivery have been the subject of a great deal of excitement and research for nearly two decades. In particular, the application of microneedles to accessing and analyzing dermal interstitial fluid, in lieu of venous blood, could greatly facilitate point-of-care diagnosis and health monitoring in austere environments. However, there have been only a few successful demonstrations of in vivo collection of ISF from human skin using a microfabricated needle array. In this paper we present an empirically determined requisite feature of microfabricated hollow silicon needles that enable collection of ISF from human skin during in vivo testing. Success was only achieved by microneedles with this specific geometric feature, or shape. To inform microneedle design and fabrication, a silicon etch simulation program was developed to predict 3D shape evolution. The microfabrication process, a simulation example and in vivo test results are presented.

Synchytrium endobioticum is a parasitic fungus that is considered to be the most important potato pathogen worldwide. Spread of the fungus can result in catastrophic impacts to agriculture and economy, as it is very infective and can survive in spore form for over 70 years. To date, the gold standard for S. endobioticum identification relies on visual classification by highly trained personnel. This paper presents the colorimetric detection of S. endobioticum from potato wart samples using a peptide nucleic acid (PNA) probe and a cyanine dye. A segment of the 18S ribosomal RNA gene was sequenced for several S. endobioticum pathotypes and used to design a species-specific PNA probe. The probe was used in a rapid colorimetric hybridization assay that detected RNA from infected wart tissue down to 10−17 mol within 15 min. This technique demonstrates potential for rapid identification of potato wart in non-laboratory settings with minimally trained staff.

A silicon microneedle array with integrated microfluidic channels is presented, which is designed to extract dermal interstitial fluid (ISF) for biochemical analysis. ISF is a cell-free biofluid that is known to contain many of the same constituents as blood plasma, but the scope and dynamics of biomarker similarities are known for only a few components, most notably glucose. Dermal ISF is accessible just below the outer skin layer (epidermis), which can be reached and extracted with minimal sensation and tissue trauma by using a microneedle array. The microneedle arrays presented here are being developed to extract dermal ISF for off-chip profiling of nucleic acid constituents in order to identify potential biomarkers of disease. In order to assess sample volume requirements, preliminary RNA profiling was performed with suction blister ISF. The microneedles are batch fabricated using established silicon technology (low cost), are small in size, and can be integrated with sensors for on-chip analysis. This approach portends a more rapid, less expensive, self-administered assessment of human health than is currently achievable with blood sampling, especially in non-clinical and austere settings. Ultimately, a wearable device for monitoring a person’s health in any setting is envisioned.

Embryonic development of the spinal cord proceeds through a carefully orchestrated temporal and spatial sequence of chemical cues to provide precise patterning of adult cell types. Recreating this complex microenvironment in a standard cell culture dish is difficult, if not impossible. In this paper, a microfluidic device is used to recapitulate, in vitro, the graded patterning events which occur during early spinal cord development. The microdevice design is developed using COMSOL modeling, with which the spatiotemporal profiles of multiple, diffusible morphogens are simulated. Four independently addressed source/sinks are employed to generate two overlapping orthogonal gradients within a cell culture chamber, mimicking the dorsoventral and anteroposterior axes of the developing embryo. Mouse embryonic stem cells are directed therein to differentiate into motor neurons in a spatially organized manner, reminiscent of a neural tube.

Rapid and specific on-site detection of disease-causing or toxin-producing organisms is essential to public health and safety. Many molecular recognition methods target ribosomal RNA sequences due to their specificity and abundance in the cell. In this work RNA targets were identified and quantified using a colorimetric bioassay. Peptide nucleic acid (PNA) probes were used to capture RNA targets, and a micrococcal nuclease digestion was performed to remove all non-target nucleic acids, including single base mismatches flanked by adenines or uracils. Perfectly-matched PNA–RNA hybrids remained intact and were detected using the symmetrical cyanine dye 3,3′-diethylthiadicarbocyanine iodide (DiSC 2 (5)). Assay applicability to complex samples was demonstrated using mixtures containing RNA sequences from two related, harmful algal bloom-causing Alexandrium species. Target RNA was detected even in mixtures with mismatched sequences in excess of the perfect match. The fieldability of the assay was tested with a portable two-wavelength colorimeter developed to quantify the dye-indicated hybridization signal. The colorimeter sensing performance was shown to be comparable to a laboratory spectrophotometer. This quick, inexpensive and robust system has the potential to replace laborious identification schemes in field environments.

A simple, effective, and universal model is presented for the formation of silicon nanowires during silver metal assisted chemical etching of silicon. The model explains nanowire formation in terms of well-known and well-understood principles of electrochemical exchange current densities at silver metal/solution interfaces, silicon/silver ion reaction kinetics, and diffusion limited aggregatoon (DLA) kinetics. The role of the metal in the formation of nanowires is clearly defined and the model is easily extended to other transition metal systems, including: Pt, Au and Pd.

A simple, two-step method of producing stable and functional peptide nucleic acid (PNA)-conjugated gold nanoparticles using a surfactant stabilization step is presented. PNA are DNA analogs with superior chemical stability and target discrimination, but their use in metallic nanoparticle systems has been limited by the difficulty of producing stable colloids of nanoparticle–PNA conjugates. In this work, the nonionic surfactant Tween 20 (polyoxyethylene (20) sorbitan monolaurate) was used to sterically shield gold surfaces prior to the addition of thiolated PNA, producing conjugates which remain dispersed in solution and retain the ability to hybridize to complementary nucleic acid sequences. The conjugates were characterized using transmission electron microscopy, dynamic light scattering, and UV–visible absorbance spectroscopy. PNA attachment to gold nanoparticles was confirmed with an enzyme-linked immunoassay, while the ability of nanoparticle-bound PNA to hybridize to its complement was demonstrated using labeled DNA.

This article reports a microfluidic device for the generation of stable, steady-state, user-defined concentration profiles for the long-term maintenance of stable diffusion gradients. The microinstrument allows both dynamic temporal and dynamic spatial control over user-defined concentrations and concentration gradients of multiple chemicals. With this device, one can create an in vitro environment capable of approximating the complex in vivo biological condition for cellular studies. In addition, the device has potential application in combinatory drug discovery, electrophoretic applications, ligand binding, etc. 3D computer simulations and analysis of arbitrary concentration profiles are presented along with experimental validation using multiple diffusing species.

Hemolymph from the American lobster (Homarus americanus) was analyzed by optical spectroscopy for the concentration of total hemolymph proteins and results were compared with a more traditional technique: refractometry. Absorbance peaks at 280 nm for total hemolymph protein concentration and 334 nm for hemocyanin concentration were studied, compared with equivalent refractometry readings, and correlated to the vitality of the lobster. These spectroscopic measurements constitute engineering data in the design a future noninvasive, field-deployable microinstrument to sort lobster according to their health and long-term viability.

Nanopore DNA sequencing devices show promise for rapidly decoding genetic information, although single nucleotide detection appears to be beyond the sensitivity of present transmembrane current measurement schemes. In this paper, a nanodevice combining nanoelectrodes with a nanopore was made to measure the nucleotide dependent transverse tunneling currents during the translocation of DNA through the nanopore. A custom high speed, low noise, integrated circuit current amplifier was designed and fabricated to measure the tunneling current. This nanodevice was characterized electrically using 2 nm to 20 nm gold nanoparticles as an artificial construct for DNA using both DC and AC detection schemes. Measured transverse tunneling currents were found to be quantized, probably according to the number of nanoparticles residing within the pore.

Polydimethylsiloxane (PDMS) polymers incorporating pendant cinnamate groups have been synthesized and evaluated for their ability to form patterned thin films via photo-crosslinking. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3482–3487, 2008

Embryogenesis is a highly regulated process in which the precise spatial and temporal release of soluble cues directs differentiation of multipotent stem cells into discrete populations of specialized adult cell types. In the spinal cord, neural progenitor cells are directed to differentiate into adult neurons through the action of mediators released from nearby organizing centers, such as the floor plate and paraxial mesoderm. These signals combine to create spatiotemporal diffusional landscapes that precisely regulate the development of the central nervous system (CNS). Currently, in vivo and ex vivo studies of these signaling factors present some inherent ambiguity. In vitro methods are preferred for their enhanced experimental clarity but often lack the technical sophistication required for biological realism. In this article, we present a versatile microfluidic platform capable of mimicking the spatial and temporal chemical environments found in vivo during neural tube development. Simultaneous opposing and/or orthogonal gradients of developmental morphogens can be maintained, resulting in neural tube patterning analogous to that observed in vivo., Summary: A microfluidic device mimics the spatial and temporal environment of neural tube development in vivo and enables the correct spatial organization of neural tube formation from stem cells in vitro.

Thermally actuated, bistable, snapping membranes have been fabricated on a silicon wafer and tested. Nonlinear finite element analysis has been used to gain an understanding of the thermomechanical behavior of these devices. A unique feature of these membranes is that they buckle downward with an increase in temperature beyond a critical value, and remain in the downward buckled state as the temperature decreases back to its initial value. The demonstration devices consist of 2 mm2, 3–4 µm thick silicon membranes with a 1 µm thick layer of silicon dioxide grown on one side and a 3 µm thick layer of aluminum deposited onto the other side. The critical snapping temperature range is measured to be 55 °C ± 5 °C. The snapping temperature is varied by changing the membrane dimensions and/or the materials used to realize the composite membrane structure. Applications to thermal actuation devices and temperature indicators are envisioned.

A miniature linear synchronous motor was designed, fabricated and tested. Actuation was achieved through interaction of traveling magnetic wave, generated by linear array of microcoils on the stator, and permanent magnets on the rotor. Two configurations of the motor were investigated. One with a single hand-assembled permanent magnet on rotor and corresponding array of multiturn microcoils; the other, a fully microfabricated rotor with embedded array of screenprinted permanent magnets and a linear array of serpentine microcoils on the stator. Motion of the rotor was constrained by dovetail microjoints. A numerical model was developed for modeling and dynamic control. The motor was tested under various operating conditions with both open- and closed-loop control. The motors showed reliable translation over 6 cm travel with accuracy limited by the feedback system.

The general design, fabrication, and development of an electrostatic translational microstage based on the inchworm principal of actuation is presented. The microstage is incorporated in a complete microsystem package that allows long range translation of the microstage through consecutive clamping to either an oscillating driver arm or stationary substrate. Actuation step size is user adjustable from 0.05 to 2 μm through the addition of a supplementary electrostatic actuator that controls the oscillation amplitude of the driver arm. Voltage to the microstage is delivered through coupled series capacitors allowing all external electrical connections to reside on the stationary substrate and allowing the microstage to translate free from the mechanical disturbances caused by direct electrical wiring. The inchworm microsystem is capable of arbitrarily large translation distances with nanometer resolution.

This paper presents the design, fabrication and testing of a hollow microneedle array with integrated, fluidic microchannels. The microneedles are machined from single crystal silicon to a shank height of 250–350 μm with 300 μm center-to-center spacing. The needle size, density and shape are controlled by independent processing steps. Piercing of the protective stratum corenum layer of the skin by the microneedles, providing access to the living epithelial layers underneath, is successfully demonstrated. Filling of the integrated microchannels by capillary action with both non-biological fluids (glycerol, ethanol, surrogate interstitial fluid (ISF) and water) as well as biological fluids (ISF and whole blood) is demonstrated. The ability to extract interstitial fluid from human skin is successfully achieved and verified by the in situ measurement of glucose concentration. The microchip presented here represents the first step towards the realization of a transdermal, ISF extraction and analysis microsystem.

Deep reactive ion etching (DRIE) is employed to fabricate mechanically interlocking structures through which high-density fluidic interconnections are provided between microchannel-containing substrates. The geometric versatility that is achievable with DRIE facilitates the fabrication of high density interconnects of two types: (1) structures with mechanically interlocking “fins” used to align arbitrarily placed fluidic via holes and (2) interlocking hole and notched cylinder pairs that accomplish mechanical and fluidic interconnect in the same structure. Both types of interconnects are tested using silicon microfluidic circuit boards with off-chip coupling for flow control and measurement, and components that consist of simple channel arrays. The “fin” and notched cylinder/hole interconnects are tested up to pressures of 100 kPa and 70 kPa, respectively.

Reversible tubing connections for glass micro-fluidic systems are realized using electro-chemical discharge machining of three-dimensional glass vias. The connections reversibly connect standard sized plastic tubing to holes in borosilicate microscope slides. Tubing connections are demonstrated on a sealed, micro-fluidic channel which is fabricated between two glass slides using SU-8. The connections are experimentally tested to withstand up to 30 psi (~206 kPa) of air pressure without leaking.

Sensitive, free-standing micromachined thermopiles have been realized in silicon by taking advantage of the high, inverse Seebeck effects of n- and p-type silicon. The thermopiles are easily fabricated with a minimal amount of microfabrication by interlocking and bonding an array of n- and p-type microjoints that are either cut or etched into silicon wafers. Prototype thermopile arrays of 35–92 couples have been fabricated and show temperature sensitivities between 19 and 45 mV/°C, respectively. It is estimated that thermopiles with as many as 1000 junctions may be produced using this fabrication method, with resulting sensitivities as high as 500 mV/°C.

This paper reports a novel, new means of mechanically lysing algae using a microfabricated, flow-driven grinding mill. The mill is demonstrated to be effective in the mechanical lysis of the dinoflagellate genus Alexandrium, a neurotoxin producing algae, responsible for Red Tide and paralytic shellfish poisoning. Pre and post milling cell counts revealed lysing efficiencies as high as 96%. Selective amplification of lysate samples was successfully performed, using Polymerase Chain Reaction (PCR) and primers specific to Alexandrium, demonstrating that the released DNA is suitable for downstream analysis.

Microfabrication technology is implemented to realize a versatile platform for the study of endothelial cell (EC) shape and function. The platform contains arrays of microchannels, 25–225 μm wide, that are fabricated by deep reactive ion etching (DRIE) of silicon and anodic bonding to glass and within which ECs are cultured. Silicon fluidic port modules, fabricated using a combination of silicon fusion bonding and anisotropic etching in KOH, provide a simple and reversible means of coupling, via standard tubing, between an individual microchannel and off-platform devices for flow monitoring and control. For flow experiments where a well-defined flow field is required, the channels are capped with either a glass lid or a thin, self-sealing elastomer membrane that can be punctured to provide direct access to cells within the microchannels. Under static culture conditions, bovine aortic ECs (BAECs) become progressively more elongated as the channel width decreases. The shape index, a dimensionless measure of cell roundness, decreases from 0.75±0.01 (mean±SEM) for BAECs cultured in 225 μm-wide microchannels to 0.31±0.02 in 25 μm-wide channels. When cuboidal BAECs are grown in 200 μm-wide microchannels and then subjected to a fluid shear stress of approximately 20 dyne/cm2 (2 Pa), they progressively elongate and align in the direction of flow in a similar manner to cells cultured on plain surfaces. To demonstrate the utility of the microfabricated platform for studying aspects of EC function, whole-cell patch-clamp recordings were performed under static conditions in open microchannels. The platform is demonstrated to be a versatile tool for studying relationships between EC shape and function and for probing the effect of flow on ECs of different shapes. Specific future applications and extensions of platform function are discussed.

This paper describes the development of an interferometric pressure transducer using a single etalon fringe as an intensity mode signal for a deflectable silicon diagram. The last fringe before the mechanical contact of the two etalon surfaces is employed, thus, providing an integral overpressure limit. The etalon design permits the illumination source to be only approximately monochromatic thereby allowing a conventional LED to be used in place of the laser diode normally required in interferometric designs and greatly simplifies the pressure sensor and instrumentation package.

MEMS technology is expanding into increasingly diverse applications. As part of a micropropulsion system, microthruster attitude controls have been micromachined in silicon. This paper presents the microthruster design, fabrication, and test results. Fluid injected into a microchamber is vaporized by resistive silicon heaters. The exiting vapor generates the thruster force as it exits a silicon micro-nozzle. The vaporization chamber, inlet and exit nozzles were fabricated using anisotropic wet etching of silicon. With a 5 W heater input, injected water could be vaporized for input flow rates up to a maximum of 0.09 cc/s. Experimental testing produced thruster force magnitudes ranging from 0.15 mN to a maximum force output of 0.46 mN depending on fabrication parameters: chamber length, nozzle geometries, heater power, and liquid flow rates.

In this paper a low cost, multi-channel separation and detection system is reported for use in fast, high throughput screening of bioanalytes. Applications include genetic engineering and drug discovery, particularly combinatorial chemistry. A prototype detection system is presented which is comprised of an array of 50 microchannels fabricated on 25 mm×75 mm glass substrates with planar, thin film metal electrodes for electrophoresis and electrochemiluminescence excitation. Fluidic interconnects to the microchannels via standard tubing provide quick and facile interfacing to external macro components, controllers and/or other microsystems. The fabrication process is readily scalable to higher density arrays.

Electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) in water only, without any added electrolyte or reducing agents, has been obtained at carbon interdigitated microelectrode arrays (C-IDAs) of 2 μm width and spacing. In a generation/collection biasing mode, ECL can be clearly seen with the naked eye in normal room lighting at concentrations greater than 1 mM. Using a conventional photomultiplier tube (PMT), a detection limit of 10(-)(7) M Ru(bpy)(3)(2+) has been achieved for an electrode area of 0.25 mm(2). In comparison, the ECL intensity produced at Pt-IDA of the same geometry, under identical experimental conditions, was more than 300 times less. The ECL obtained at C-IDAs is attributed to the annihilation reaction of the reduced and oxidized forms of the Ru(bpy)(3)(2+) made possible due to the small electrode spacing.

A physical model is presented which quantitatively describes the threshold voltage instability, commonly known as drift, in n-channel Si3N4-gate and as well as Al2O3-gate pH ISFETs. The origin of the so-called drift is postulated to be associated with the relatively slow chemical modification of the gate insulator surface as a result of exposure to the electrolyte. The chemical modification of the surface is assumed to result from a transport-limited reaction whose rate is modeled by a hopping and/or trap-limited transport mechanism known as dispersive transport. The change in the chemical composition of the insulator surface leads to a decrease in the overall insulator capacitance with time, which gives rise to a monotonic temporal increase in the threshold voltage.

The detection and quantification of DNA strands using an electrochemiluminescence (ECL) instrument with a microfabricated excitation/detection cell is presented. The microcell is a vertical assembly of silicon and glass substrates, containing thin film Pt electrodes and micromachined fluid channels. A silicon PIN diode photodetector completes the cell assembly. The DNA strands are labeled with an electrochemically exited, luminescing molecule: tris (2,2′ bipyridyl) ruthenium (TBR). The labeled DNA strands are bound to paramagnetic beads with a biotin–streptavidin linkage. The magnetic beads are attracted to the Pt electrode surface with an external magnet, where ECL is excited. With a 1 cm 2 , Pt anode, a detection limit of 40 fmol of DNA is obtained with a silicon PIN diode photodetector operating at room temperature. The overall size of the microcell is only 1.5 cm×2 cm×0.2 cm and supports a sample volume of 150 μl. This is the first demonstration of DNA quantification using an ECL microinstrument.

A physical model is presented which quantitatively describes the threshold voltage instability, commonly known as drift, in n-channel Si/sub 3/N/sub 4/-gate pH ISFET's. The origin of the so-called drift is postulated to be associated with the relatively slow conversion of the silicon nitride surface to a hydrated SiO/sub 2/ or oxynitride layer. The rate of hydration is modeled by a hopping and/or trap-limited transport mechanism known as dispersive transport. Hydration leads to a decrease in the overall insulator capacitance with time, which gives rise to a monotonic temporal increase in the threshold voltage.

A new hybrid technology for fabricating, interconnecting, and assembling microdevices is introduced. This new technology is predicated on the creation of dimensionally scaled manufacturing and assembly techniques and has been coined ‘MicroJoinery’ as a descriptive designation. MicroJoinery, along with its collected ‘toolbox’ of associated microfabrication techniques, allows for the facile realization of a widely divergent collection of microsystem components including: fluidic microvalves, microfluidic interconnects, microreaction chambers, xyz positioning microstages, fiber-optic switches, etc. Additionally, MicroJoinery provides a new paradigm for design and practical assembly of microsystems. This paper explores the applications of MicroJoinery by presenting several examples of microdevices and microsystems tractable through MicroJoinery.

An array of high-energy particle detectors, or pixels, has been realized in a silicon substrate using microfabrication technology. A process for fabricating a hemispherical anode, 100 μm in diameter, is described. The pixels are operated in a gaseous chamber where electrons, released when a gas molecule is ionized by an incident high-energy particle, are amplified through a gas avalanche process, and induce a voltage signal at the pixel anode. Test results obtained when operating in the presence of an 55 Fe source indicate that the voltage signal is proportional to the energy of incident γ-rays. The microfabricated array has several advantages over existing gaseous pixel detectors, including high gain at lower applied voltage, reproducible geometry, and potentially lower manufacturing cost.

We describe the microfabrication, packaging, and testing of an active, dry, scalp electroencephalogram (EEG) electrode. The electrode consists of a silicon sensor substrate and a custom circuit substrate (2 μm CMOS technology). A via-hole technology has been developed using reactive ion etching with SF 6 O 2 gas mixture to make electrical contacts between the sensor and circuit substrates. These substrates and batteries (power source) are then assembled in a custom package for testing on bench and human subjects.

Rapid and cost-effective DNA sequencing is a pivotal prerequisite for the genomics era. Many of the recent advances in forensics, medicine, agriculture, taxonomy, and drug discovery have paralleled critical advances in DNA sequencing technology. Nanopore modalities for DNA sequencing have recently surfaced including the electrical interrogation of protein ion channels and/or solid-state nanopores during translocation of DNA. However to date, most of this work has met with mixed success. In this work, we present a unique nanofabrication strategy that realizes an artificial nanopore articulated with carbon electrodes to sense the current modulations during the transport of DNA through the nanopore. This embodiment overcomes most of the technical difficulties inherent in other artificial nanopore embodiments and present a versatile platform for the testing of DNA single nucleotide detection. Characterization of the device using gold nanoparticles, silica nanoparticles, lambda dsDNA and 16-mer ssDNA are presented. Although single molecule DNA sequencing is still not demonstrated, the device shows a path towards this goal.

Stochastic molecular sensors based on resistive pulse nanopore modalities are envisioned as facile DNA sequencers. However, recent advances in nanotechnology fabrication have highlighted promising alternative detection mechanisms with higher sensitivity and potential single-base resolution. In this paper we present the novel self-aligned fabrication of a solid-state nanopore device with integrated transverse graphene-like carbon nanoelectrodes for polyelectrolyte molecular detection. The electrochemical transduction mechanism is characterized and found to result primarily from thermionic emission between the two transverse electrodes. Response of the nanopore to Lambda dsDNA and short (16-mer) ssDNA is demonstrated and distinguished.

Microwave sintering of ceramics in multimode cavities, particularly the use of picket-fence arrangements, has recently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique "microwave effect" has been observed. At present, various aspects of the sintering profess such as preparation of sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as SiC rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide an improved understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process. In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a ceramic loading plate placed at the base of the cavity. >

This paper describes the design, fabrication and testing of a prototype dry surface electrode for EEG signal recording. The new dry electrode has the advantages of no need for skin preparation or conductive paste, potential for reduced sensitivity to motion artifacts and an enhanced signal-to-noise ratio. The electrode's sensing element is a 3 mm stainless steel disk which has a 2000 A (200 nm) thick nitride coating deposited onto one side. The back side of the disk is attached to an impedance converting amplifier. The prototype electrode was mounted on a copper plate attached to the scalp by a Velcro strap. The performance of this prototype dry electrode was compared to commercially available wet electrodes in 3 areas of electroencephalogram (EEG) recording: (1) spontaneous EEG, (2) sensory evoked potentials, and (3) cognitive evoked potentials. In addition to the raw EEG, the power spectra of the signals from both types of electrodes were also recorded. The results suggest that the dry electrode performs comparably to conventional electrodes for all types of EEG signals analysis. This new electrode may be useful for the production of high resolution surface maps of brain activity where a large number of electrodes or prolonged recordingtimes are required.

A high sensitivity, batch fabricated, fiber-optic pressure sensor has been fabricated using silicon micromachining technology. The transducer consists of a fiber positioning v-groove, a 45° stationary mirror and a silicon membrane, micromachined in silicon by anisotropic etching in KOH solution, and a single mode optical fiber. The membrane and optical fiber end form a Fabry-Perot cavity whose length varies with pressure. The generated optical interference fringes are used to detect and measure the change in membrane deflection. Pressure range of operation is dictated by the thickness, size and material of the membrane. The sensor described here was designed for low pressure range (0–25 mm Hg) applications. Temperature sensitivity and stability problems which are commonly encountered with currently available piezoresistive and capacitive pressure sensors are significantly reduced by the inherent differential nature of interferometric measurement and the use of all silicon construction. The fabrication, packaging and testing of the sensor are described in this paper. The performance of the sensor was evaluated and found to compare favorably with theoretical predictions.

The microfabricated surface plasmon sensor is a hybrid system that integrates optical, mechanical and electronic components. The sensor contains elements that are common to numerous electro-optical systems, creating a miniature optical bench. The microsystem elements include a single-mode optical fiber, a graded index collimating lens, a scanning rotating micro-mirror, a cavity filled with index matching fluid, and a position sensitive photodiode. The elements are both laterally and vertically aligned using multi-substrate bonding and positive component-to-component alignment.

The real-time detection of harmful algal bloom (HAB)-causing organisms is crucial to preventing human illness and death, animal mortalities, and significant economic losses for coastal and fishing communities. However, most identification schemes are time-consuming and costly, which limit their use for rapid risk assessment. To address this problem, a simple colorimetric test for the HAB-causing Alexandrium fundyense/tamarense/catanella dinoflagellate species complex is presented. This work integrates an indicator dye-based bioassay for detecting toxigenic Alexandrium RNA with a custom-built two-color detector. A peptide nucleic acid (PNA) probe is used to capture target RNA, and the formation of the PNA-RNA duplex is visible as a solution color change from blue to purple with the addition of the cyanine dye 3,3′-diethyldithiacarbocyanine iodide (DiSC 2 (5)). PNA-RNA hybridization and discrimination against mismatched sequences is achieved within minutes at 25°C. Hybridization signals obtained from the colorimeter are comparable to those from a benchtop spectrophotometer. The advantages of this method represent a step towards field-compatible, easy-to-use and inexpensive detection schemes that require minimal training for successful use.

The morphology of porous silicon is studied by scanning electron microscopy (SEM) by making an oxide replica of the pore structure. Highly branched n-type porous silicon samples were prepared and a replica was formed by oxidation of the pores followed by selective removal of the silicon substrate to expose the oxide pores. Scanning and transmission electron microscopy images confirmed many previously held assumptions about porous silicon formation, including the fractal structure and crystallographic propagation; they also provided a clearer understanding of the details of pore formation. The replica procedure also provides a platform for a more facile and comprehensive analysis of the porous silicon morphology.

Recent reports describing photoluminescence in porous silicon have heightened the level of interest in it as a unique electronic material, and have created a need for a more complete understanding of the mechanism of porous silicon formation. The various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon. Because the specific surface dissolution chemistry is critical for a complete understanding of pore formation, some of the more prominent dissolution reactions are also reviewed and their relative importance to pore generation and morphology is discussed. Some aspects of the recently reported quantum effects are also reviewed. Because the mechanism of porous silicon formation involves a wide range of interdisciplinary fields, a considerable number of analogies and examples to related phenomena ...

This is the first report of a transverse carbon nanoelectrode for sensing translation events through a solid state nanopore. This device has application to the study of molecular transport and DNA sequencing. The device is fabricated on a silicon nitride membrane using electron beam stimulated oxidation of carbon (EBSOC) to first create a carbon nanowire. The nanowire is then encapsulated in a top layer of silicon nitride. A nanopore is then milled through both the silicon nitride membrane and carbon nanowire using a high energy transmission electron microscope (TEM) or a focused ion beam (FIB). This creates a pair of electrodes that are self-aligned to the nanopore. With state-of-the-art FIB techniques pores and electrode gaps ≥ 10nm are achieved. In this report the results of electrical testing of a device with a 25nm pore are presented, including current-voltage characterization in air and the detection of a nanoparticle translocating the nanopore in solution.

Marine dinoflagellates of the genus Alexandrium can produce dangerous amounts of paralytic shellfish toxins at such low cell densities that water discoloration often associated with harmful algal blooms is not always evident, making detection of blooms during early stages extremely important. Our research focuses on developing a new method of molecular detection for multiple species of Alexandrium using peptide nucleic acid (PNA) probes and surface plasmon resonance. Results thus far indicate that this method yields reliable detection of perfectly complimentary oligonucleotide sequences specific to A. fundyense, A. tamarense, A. catenella, and A. ostenfeldii with no detection of non-complimentary sequences, as well as very good discrimination between negative control PNA probes and Alexandrium-specific PNA probes. We have also been able to regenerate the probe layer on the sensor surface for use in multiple assays by removing the target DNA, making this method economical in the long run.