Thrust III – Low Power Wearable Nanosensors

In this thrust, our primary goal is to develop a diverse an array of ultra-low-power sensors for correlated monitoring of environmental and physiological parameters.  Ultra-low power sensors are essential for self-powered wearables and the projects in this thrust rely on nanotechnology to achieve this goal.The sensors currently under investigation include gas, bioelectric, biophotonic and biochemical sensors. The projects in this thrust rely on nanotechnology to create ultra-low-power sensor systems, which is essential for self-powered operation.

For gas sensors two distinct approaches are currently being pursued to address different analytes: 1) ALD-based metal-oxide nanolayers operating at room temperature for sensing ozone, nitrous oxide, and nitrogen dioxide; 2) Polymer functionalized mechanical resonators for detection of volatile organic compounds (VOCs).  For mechanical resonance based sensing we use capacitive micromachined ultrasonic transducers (CMUTs) as they offer advantages of massive parallelism, large sensing area, vacuum cavity, and high quality factor compared to cantilevers. The major challenges in our gas sensor development efforts are minimizing power dissipation, maximizing the selectivity, and translating the results from the lab to practical use.

For biochemical sensing, we are exploring sweat sampling for non-invasive monitoring of glucose, lactose and similar analytes.  We are developing two major approaches to implement a biocompatible, reliable, conformal, and practical skin interface for sweat collection: 1) a hydrogel-based capillary-osmotic pump and 2) a nanocellulose layer with printed sensor structures.

The bioelectrical sensors area is relatively well established, as ExG electrodes for biopotential measurements have long been commercially available. Our efforts in this direction have aimed incorporation of adhesive-less dry electrodes in comfortable and wearable low-power bioelectric sensing systems. As another type of a bioelectrical sensor, we have developed skin hydration sensors by patterning silver nanowire based electrodes on soft materials such as Polydimethylsiloxane (PDMS).
Optical sensing approaches, specifically pulse oximetry and photoplethysmography (PPG) at the early phase have been developed using commercial off-the-shelf (COTS) components. The power reduction has been mainly achieved by system level optimization.