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Here, we introduce a microchip for differential measurements of aqueous samples in twin calorimetric arms with a sub-nL enclosed space. Each arm features a fluidic microchannel located in close proximity to a thin-film resistance thermometer and heater patterned on a low-stress SiN membrane held over a Si cavity with suspension beams. The chip exhibits a rapid response with a thermal time constant of less than 10 ms in atmosphere and a residual thermal conductance below $6{\mu }\text{W}{\cdot }\text{K}^{-1 }$ , one of the lowest reported and accounts for the excellent sensitivity registered in vacuum up to 11 $\text{V}{\cdot }\text{W}^{-1 }$ . These values are in good agreement with those ones predicted by modeling using finite element method, lumped-capacitance analysis, and calorimeter electrothermal circuit simulation together with the measurement system. Long suspension beams in each arm ensure uniform temperature maintained across its membrane as revealed by the fluorescence-based melting curve analysis. We share the specific heat capacity values of water, glycerin, and mineral oil accurately measured by the chip. Lastly, we demonstrate the chip calorimeter utility on the measurement of the photothermal transduction efficiency of plasmonic nanoparticles, which makes our study further unique in expanding the applications of chip calorimeters. [2021-0044]

A dual-channel flow-through microcalorimeter device is presented along with a non-contact precision method of temperature calibration. A microfluidic channel with a volume of ≈550 pL in a spiral layout was fabricated from low-stress nitride suspended over a cavity in a silicon substrate. The thin-film heater and resistive temperature detector (RTD) on the channel were defined by a patterned Ti layer. The device exhibited a rapid thermal response with the following thermal characteristics: a time constant of ≈10.5 ms, a heat conductance of $\approx 152~\mu ~\text{W}\,\cdot ~{\mathrm {K}}^{-{1}} $ and a heat capacitance of $\approx 1.6~\mu \text{J}\,\cdot {\mathrm {K}}^{-{1}} $ on average based on the measurements of nine separate units fabricated on the same wafer. Further, the melting curve analysis (MCA) of a double-stranded DNA was proposed as a non-contact method of microcalorimeter RTD calibration. The method revealed that the measurement by the RTD underestimates the temperature of the channel interior by an amount of nearly 15%, at ≈ 9 mW. At this dissipated power level, the method also revealed a spatial nonuniformity of ≈ ± 0.8 °C across the microcalorimeter. [2020-0173]

This paper describes the design, the fabrication, and the characterization of an interdigitated 3-D silicon (Si) ring microelectrodes for dielectrophoretic (DEP) manipulation of particles. The 3-D microelectrodes are derived from a high-aspect-ratio comb structure etched in a doped single crystal Si on an insulating dielectric (silicon-on-insulator). Fingers of the comb are evolved into ring microelectrodes once perforated with a linear array of well-defined round lateral constrictions. This is achieved by the segmented finger layout and the Si dry release strategy borrowed from inertial microelectromechanical systems. The fingers and their interspaces are sealed with a cover layer forming a microfluidic flow chamber surrounded by 3-D microelectrodes and accessible via single inlet/outlet. The functionality of the device has been verified on 2- and 10-μm polystyrene microspheres in pressure-driven flow through the ring microelectrodes at 3.3 μL/min effectively focusing them into streams or trapping them around the fingers at moderate voltage levels (20-40 Vpp).

This paper gives a brief overview of silicon-based microfluidic platforms developed over the years by our group for the extraction, amplification, and detection of the nucleic acids. Extraction of both the genomic and viral nucleic acids from whole blood has been demonstrated on Si-based microfluidics. Rapid amplification has been achieved by polymerase chain reaction in Si-based thermal reactors (micro-PCR). Detection has been realized by a chip-to-chip integration of the micro-PCR and micro capillary electrophoresis (micro-CE).

Recent success of microelectromechanical systems (MEMS) in projection displays have raised similar expectation for an efficient, low power, affordable, full-page and pneumatic tactile display. Such design has not been achieved by the conventional technology but could bring significant improvement to current refreshable Braille displays. This paper demonstrates a novel bulk-micromachined electrostatic microvalve suitable for a pneumatic tactile display. The microvalve, a silicon perforated diaphragm juxtaposed to a silicon inlet orifice, requires relatively low closing voltage against a large supply differential pressure and flow rate, i.e., 72.9 V-rms for 19.3 kPa and 85 mi/min. Such an attractive characteristic is due to its unique curved-compliant structure that has, unlike other electrostatic microvalves, no tolerance for any initial air gap between its electrodes. As a design tool, a mechanical model of the microvalve is introduced based on the lubrication theory and large plate deflection theory. The model is established on a steady-state coupled field problem of fluid-solid mechanics. Reynolds and von-Karman equations were simultaneously solved for the microvalve geometry by finite difference approximation and double Fourier series expansion. The results of the model and experiments are compared and found to be in good agreement with a relative error less than 10%.