Microfabricated thermal modulator for comprehensive two-dimensional micro gas chromatography: design, thermal modeling, and preliminary testing.

In comprehensive two-dimensional gas chromatography (GC x GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, thereby enhancing the resolution and the selectivity of analytes. As part of an effort to develop a microGC x microGC prototype, in this report we present the design, fabrication, thermal operation, and initial testing of a two-stage microscale thermal modulator (microTM). The microTM contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimension column in a rapid, programmable manner.

A neural amplifier with high programmable gain and tunable bandwidth.

A neural recording amplifier having programmable gain and bandwidth is presented. The gain can be digitally programmed using 6 bits from 100x to 1100x in steps of 100x. The low-frequency cutoff can be varied from less than 10Hz to above 100Hz to accept or reject field potentials while the high-frequency cutoff is fixed at 9kHz.

High-density cochlear implants with position sensing and control.

Silicon-based thin-film technology has been used to develop high-density cochlear electrode arrays with up to 32 sites and four parallel channels of simultaneous stimulation. The lithographically-defined arrays utilize a silicon-dielectric-metal-parylene structure with 180 microm-diameter IrO sites on 250 microm centers. Eight on-board strain gauges allow real-time imaging of array shape during insertion, and a tip sensor measures forces on any structures contacted in the scala tympani (e.

Model of vapor-induced resistivity changes in gold-thiolate monolayer-protected nanoparticle sensor films.

An investigation of the modulation of charge transport through thin films of n-octanethiolate monolayer-protected gold nanoparticles (MPN) induced by the sorption of organic vapors is presented. A model is derived that allows predictions of MPN-coated chemiresistor (CR) responses from vapor-film partition coefficients, and analyte densities and dielectric constants. Calibrations with vapors of 28 compounds collected from an array of CRs and a parallel thickness-shear-mode resonator are used to verify assumptions inherent in the model and to assess its performance.

A low-profile three-dimensional silicon/parylene stimulating electrode array for neural prosthesis applications.

This paper describes a low-profile three-dimensional silicon/parylene microelectrode array as basis for practical neural prostheses for use in the central nervous system. The circuit areas of the silicon probes, containing mixed-signal CMOS circuitry for neural stimulation/recording, can be folded over to reduce the overall height of the microassembled array above the cortical surface. The low- profile structure is implemented using multiple gold beams spaced by orthogonal silicon braces.

A low-profile three-dimensional neural stimulating array with on-chip current generation.

This paper describes a low-profile silicon microelectrode array for selectively stimulating in the central nervous system. The array consists of a number of 64-site 8-channel planar CMOS probes, a platform to support the probes on the cortical surface, spacers to hold the probes orthogonal to the platform, and a hybrid chip for platform address decoding. It features integrated circuitry with on-chip current generation to deliver biphasic currents from -127 microA to +127 microA to selected sites with 1 microA resolution and fold-down structures to reduce the vertical rise above the cortex for chronic implants.

Micromachined bulk PZT tissue contrast sensor for fine needle aspiration biopsy.

This paper describes a micromachined piezoelectric sensor, integrated into a cavity at the tip of a biopsy needle, and preliminary experiments to determine if such a device can be used for real-time tissue differentiation, which is needed for needle positioning guidance during fine needle aspiration (FNA) biopsy. The sensor is fabricated from bulk lead zirconate titanate (PZT), using a customized process in which micro electro-discharge machining is used to form a steel tool that is subsequently used for batch-mode ultrasonic micromachining of bulk PZT ceramic. The resulting sensor is 50 microm thick and 200 microm in diameter.

First-generation hybrid MEMS gas chromatograph.

The fabrication, assembly, and initial testing of a hybrid microfabricated gas chromatograph (microGC) is described. The microGC incorporates capabilities for on-board calibration, sample preconcentration and focused thermal desorption, temperature-programmed separations, and "spectral" detection with an integrated array of microsensors, and is designed for rapid determinations of complex mixtures of environmental contaminants at trace concentrations. Ambient air is used as the carrier gas to avoid the need for on-board gas supplies.

Dual-chemiresistor GC detector employing monolayer-protected metal nanocluster interfaces.

The synthesis and testing of two gold-thiolate monolayer-protected (nano)clusters as interfacial layers on a dual-chemiresistor vapor sensor array are described. Responses (changes in dc resistance) to each of 11 organic solvent vapors are rapid, reversible, and linear with concentration at low vapor concentrations, becoming sublinear at higher concentrations. Limits of detection (LODs) range from 0.