David D. Allred received Alumni Professorship Award

Pulsatile bioimpedance measurements require filters with very narrow bandwidths to preserve heartbeat-rate modulation while suppressing excess noise. At the signal's carrier frequency, this demands an impractically-high-Q filter. Multirate signal processing is an attractive solution to this problem, as it provides an avenue to extract the signals of interest practically. This paper presents a multirate filtering solution and shows step-by-step how the bioimpedance data of interest are extracted from noise and excitation frequency in in-phase and quadrature signals acquired from an analog measurement circuit. The tested impedance values resemble realistic human tissue impedance, demonstrating the method's ability to measure a human pulse within an approximately 50−Hz bandwidth at a 1−MHz carrier. This method is useful for high-Q bioimpedance measurements where interest lies in the details of signals pulsing at the rate of a beating human heart.

The effects of physiologically relevant glucose concentrations on the optical properties of whole blood were measured in-vitro. A concentration increase of +400 mg/dL caused a decrease in the scattering coefficient by 10% over all wavelengths studied. To determine potential mechanisms for the change in the scattering coefficient, we employed optical microscopy to quantify the change in erythrocyte geometry. A 15% change in cell thickness was observed following a glucose increase of +500 mg/dL.

DNA-templated nanofabrication presents an innovative approach to creating self-assembled nanoscale metal–semiconductor-based Schottky contacts, which can advance nanoelectronics. Herein, we report the successful fabrication of metal–semiconductor Schottky contacts using a DNA origami scaffold. The scaffold, consisting of DNA strands organized into a specific linear architecture, facilitates the competitive arrangement of Au and CdS nanorods, forming heterojunctions, and addresses previous limitations in low electrical conductance making DNA-templated electronics with semiconductor nanomaterials. Electroless gold plating extends the Au nanorods and makes the necessary electrical contacts. Tungsten electrical connection lines are further created by electron beam-induced deposition. Electrical characterization reveals nonlinear Schottky barrier behavior, with electrical conductance ranging from 0.5 × 10^–4 to 1.7 × 10^–4 S. The conductance of these DNA-templated junctions is several million times higher than with our prior Schottky contacts. Our research establishes an innovative self-assembly approach with applicable metal and semiconductor materials for making highly conductive nanoscale Schottky contacts, paving the way for the future development of DNA-based nanoscale electronics.

High-temperature microfluidic devices (such as gas chromatography microcolumns) have traditionally been fabricated using photolithography, etching, and wafer bonding which allow for precise microscale features but lack the ability to form complex 3D designs. Metal additive manufacturing could enable higher complexity microfluidic designs if reliable methods for fabrication are developed, but forming small negative features is challenging-especially in powder-based processes. In this paper, the formation of sealed metal microchannels was demonstrated using stainless-steel binder jetting with bronze infiltration. To create small negative features, bronze infiltrant must fill the porous part produced by binder jetting without filling the negative features. This was achieved through sacrificial powder infiltration (SPI), wherein sacrificial powder reservoirs (pore size similar to 60 mu m) are used to control infiltrant pressure. With this pressure control, the infiltrant selectively filled the small pores between particles in the printed part (pore size similar to 3 mu m) while leaving printed microchannels (700 mu m and 930 mu m) empty. To develop the SPI method, a pore filling study was performed in this stainless-steel/bronze system with 370 mu m, 650 mu m, and 930 mu m microchannel segments. This study enabled SPI process design on these length scales by determining variations in pore filling across a sample and preferential filling between different sized pores.

A miniaturized short-wavelength infrared spectrometer for use with diffuse light was created by combining a thin form factor carbon nanotube composite collimator, a linear variable filter, and an InGaAs photodiode array. The resulting spectrometer measures 3 mm × 4 mm × 14 mm and shows a significant improvement in resolution over a spectrometer without the collimator when used with diffuse light. Its small size and high throughput make it ideal for applications such as wearable optical sensing, where light from highly scattering tissue is measured. Plethysmographic measurements on the wrist were demonstrated, showing rapid data collection with diffuse light.

The ability to monitor a varying impedance has a range of applications, including the measurement of biological properties using bioimpedance analysis. For this type of impedance monitoring, the human heartbeat plays a role, motivating a desire to monitor pulsatile impedance changes. A four-point circuit for pulsatile impedance monitoring is designed, simulated, and built on a PCB. The circuit design is described. The circuit's ability to measure constant impedance across frequency and extract lumped element values is characterized. Using a photoresistor setup, the circuit's response to pulsatile impedance variation ranging from 500 Ω to 70 kΩ is measured and analyzed. The measured circuit settling time for an impedance change as large as 70 kΩ is 40 milliseconds, sufficient speed for heartbeat-rate pulsatile impedance monitoring.