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We introduce a lead zirconate titanate [PZT; Pb(Zr0.52Ti0.48)O3] microdiaphragm resonating sensor packaged in a polydimethylsiloxane chip. The proposed sensor can measure the density and viscosity of a liquid that is within the density and viscosity regime of blood (1.060 × 103 kg/m3, 3–4 cP). To verify the basic characteristics of the sensor, viscous solutions were prepared from glycerol and deionized water with a density in the range from 0.998 to 1.263 × 103 kg/m3 and a viscosity in the range from 1 to 1414 cP. We measured the frequency responses of the sensor before and after injecting the viscosity- and density-controlled liquid under the bottom of the microdiaphragm. The resonant frequencies in the (1,1) and (2,2) modes decreased linearly as a function of the liquid density in the range from 0.998 to 1.146 × 103 kg/m3 with a sensitivity of 28.03 Hz/kg·m−3 and 81.85 Hz/kg·m−3, respectively. The full width at half maximum had a logarithmic relationship with the liquid viscosity in the viscosity range from 1 to 8.4 cP. The quality factor (Q-factor) for the 50% glycerol/water mixture was determined to be greater than 20 for both the (1,1) and the (2,2) modes, indicating that the microdiaphragm resonating sensor is suitable for measuring the density and viscosity of a liquid within a density range from 0.998 to 1.1466 × 103 kg/m3 and a viscosity range from 1 to 8.4 cP. These density and viscosity ranges span the regime of possible changes of blood characteristics. The microdiaphragm resonating sensors were also tested with a real human serum to verify that the sensor is suitable for measuring the viscosity and density of blood. Therefore, the PZT microdiaphragm resonating sensor could be utilized for early diagnosis of diseases associated with changes in the physical properties of blood.

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Multi-modal chemical sensors based on microelectromechanical systems (MEMS) have been developed with an electrical readout. Opto-calorimetric infrared (IR) spectroscopy, capable of obtaining molecular signatures of extremely small quantities of adsorbed explosive molecules, has been realized with a microthermometer/microheater device using a widely tunable quantum cascade laser. A microthermometer/microheater device responds to the heat generated by nonradiative decay process when the adsorbed explosive molecules are resonantly excited with IR light. Monitoring the variation in microthermometer signal as a function of illuminating IR wavelength corresponds to the conventional IR absorption spectrum of the adsorbed molecules. Moreover, the mass of the adsorbed molecules is determined by measuring the resonance frequency shift of the cantilever shape microthermometer for the quantitative opto-calorimetric IR spectroscopy. In addition, micro-differential thermal analysis, which can be used to differentiate exothermic or endothermic reaction of heated molecules, has been performed with the same device to provide additional orthogonal signal for trace explosive detection and sensor surface regeneration. In summary, we have designed, fabricated and tested microcantilever shape devices integrated with a microthermometer/microheater which can provide electrical responses used to acquire both opto-calorimetric IR spectra and microcalorimetric thermal responses. We have demonstrated the successful detection, differentiation, and quantification of trace amounts of explosive molecules and their mixtures (cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN)) using three orthogonal sensing signals which improve chemical selectivity.