Molecular bridge-mediated ultralow-power gas sensing.

We report the electrical detection of captured gases through measurement of the quantum tunneling characteristics of gas-mediated molecular junctions formed across nanogaps. The gas-sensing nanogap device consists of a pair of vertically stacked gold electrodes separated by an insulating 6 nm spacer (~1.5 nm of sputtered α-Si and ~4.5 nm ALD SiO2), which is notched ~10 nm into the stack between the gold electrodes. The exposed gold surface is functionalized with a self-assembled monolayer (SAM) of conjugated thiol linker molecules. When the device is exposed to a target gas (1,5-diaminopentane), the SAM layer electrostatically captures the target gas molecules, forming a molecular bridge across the nanogap. The gas capture lowers the barrier potential for electron tunneling across the notched edge region, from ~5 eV to ~0.9 eV and establishes additional conducting paths for charge transport between the gold electrodes, leading to a substantial decrease in junction resistance. We demonstrated an output resistance change of >108 times upon exposure to 80 ppm diamine target gas as well as ultralow standby power consumption of <15 pW, confirming electron tunneling through molecular bridges for ultralow-power gas sensing.

A Low-Profile Digital Eye-Tracking Oculometer for Smart Eyeglasses.

Wearable eye tracking devices have broad uses in medicine, psychology, augmented & virtual reality and consumer market research. Most mobile eye trackers available today utilize infrared imaging of the pupil and corneal reflections with video cameras. This tracking method requires sophisticated real-time processing of video signals consuming substantial electrical power. This method is thus unsuitable for light weight wearables such as adaptive smart eyeglasses for correction of presbyopia. In this paper we present a low-profile, low-power (7.7 mJ/sample) digital eye tracker oculometer based on infrared sclera tracking. The system is implemented using eight, 24-bit infrared proximity sensors and synchronous infrared LEDs. The pupil location is determined from 32 reflected pulsed light measurements independent of ambient illumination. The digital oculometer is 3.1 mm thick and weighs ~3 g. The tracker mounts adjacent to the tunable lenses in the smart eyeglasses frame. The eye tracker showed a pointing error of 1.3 degrees rms over a vertical and horizontal range of 30 degrees when tested by an observer.

A bubble-based microfluidic gas sensor for gas chromatographs.

We report a new proof-of-concept bubble-based gas sensor for a gas chromatography system, which utilizes the unique relationship between the diameters of the produced bubbles with the gas types and mixture ratios as a sensing element. The bubble-based gas sensor consists of gas and liquid channels as well as a nozzle to produce gas bubbles through a micro-structure. It utilizes custom-developed software and an optical camera to statistically analyze the diameters of the produced bubbles in flow. The fabricated gas sensor showed that five types of gases (CO2, He, H2, N2, and CH4) produced (1) unique volumes of 0.44, 0.74, 1.03, 1.28, and 1.42 nL (0%, 68%, 134%, 191%, and 223% higher than that of CO2) and (2) characteristic linear expansion coefficients (slope) of 1.38, 2.93, 3.45, 5.06, and 5.44 nL/(kPa (µL s(-1))(-1)). The gas sensor also demonstrated that (3) different gas mixture ratios of CO2 : N2 (100 : 0, 80 : 20, 50 : 50, 20 : 80 and 0 : 100) generated characteristic bubble diameters of 48.95, 77.99, 71.00, 78.53 and 99.50 µm, resulting in a linear coefficient of 10.26 µm (µL s(-1))(-1). It (4) successfully identified an injection (0.01 µL) of pentane (C5) into a continuous carrier gas stream of helium (He) by monitoring bubble diameters and creating a chromatogram and demonstrated (5) the output stability within only 5.60% variation in 67 tests over a month.