A MoS 2 /graphene hybrid aerogel synthesized with two-dimensional MoS 2 sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO 2 detection. The combination of graphene and MoS 2 leads to improved sensing properties with the graphene scaffold providing high specifi c surface area and high electrical and thermal conductivity and the single to few-layer MoS 2 sheets providing high sensitivity and selectivity to NO 2 . The hybrid aerogel is integrated onto a low-power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO 2 . By heating the material to 200 °C, the response and recovery times to reach 90% of the fi nal signal decrease to <1 min, while retaining the low detection limit. The MoS 2 / graphene hybrid also shows good selectivity for NO 2 against H 2 and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO 2 sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.

Low power catalytic hydrogen sensors are fabricated by functionalizing low power polysilicon microheaters with platinum nanoparticle catalyst loaded in a high surface area graphene aerogel support. Fabrication and characterization of the polysilicon microheaters are described. The platinum nanoparticle-loaded graphene aerogel is characterized by transmission electron microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The catalytic hydrogen sensors consume as little as 2.2 mW of power, have sensitivity of 1.6%/10,000 ppm hydrogen, a t 90 response and recovery time of 0.97 s and 0.72 s, respectively, a lower detection limit of approximately 65 ppm, and negligible cross sensitivity to methane, npentane, and diethylether.

A high‐surface‐area, highly crystalline boron nitride aerogel synthesized with nonhazardous reactants has been loaded with crystalline platinum nanoparticles to form a novel nanomaterial that exhibits many advantages for use in a catalytic gas sensing application. The platinum nanoparticle‐loaded boron nitride aerogel integrated onto a microheater platform allows for calorimetric propane detection. The boron nitride aerogel exhibits thermal stability up to 900 °C and supports disperse platinum nanoparticles, with no sintering observed after 24 h of high‐temperature testing. The high thermal conductivity and low density of the boron nitride aerogel result in an order of magnitude faster response and recovery times (<2 s) than reported on alumina support and allow for 10% duty cycling of the microheater with no loss in sensitivity. The resulting 1.5 mW sensor power consumption is two orders of magnitude less than commercially available catalytic gas sensors and unlocks the potential for wireless, battery‐powered catalytic gas sensing.

This paper reports a facile method for creating a nanostructured metal oxide film on a low power microheater sensor platform and the direct realization of this structure as a gas sensor. By fast annealing the deposited liquid precursors with the microheater, a highly porous, nanocrystalline metal oxide film can be generated in situ and locally on the sensor platform. With only minimal processing, a high performance, miniaturized gas sensor is ready for use. A carbon monoxide sensor using the in situ synthesized porous tin oxide (SnO2) sensing film is made as a demonstration of this technique. The sensor exhibits a low detection limit and fast response and recovery time at a low operating temperature. This facile fabrication method is highly flexible and has great potential for large-scale gas sensor fabrication.

A simple and versatile strategy is presented for the localized on-chip synthesis of an ordered metal oxide hollow sphere array directly on a low power microheater platform to form a closely integrated miniaturized gas sensor. Selective microheater surface modification through fluorinated monolayer self-assembly and its subsequent microheater-induced thermal decomposition enables the position-controlled deposition of an ordered two-dimensional colloidal sphere array, which serves as a sacrificial template for metal oxide growth via homogeneous chemical precipitation; this strategy ensures control in both the morphology and placement of the sensing material on only the active heated area of the microheater platform, providing a major advantage over other methods of presynthesized nanomaterial integration via suspension coating or printing. A fabricated tin oxide hollow sphere-based sensor shows high sensitivity (6.5 ppb detection limit) and selectivity toward formaldehyde, and extremely fast response (1.8 s) and recovery (5.4 s) times. This flexible and scalable method can be used to fabricate high performance miniaturized gas sensors with a variety of hollow nanostructured metal oxides for a range of applications, including combining multiple metal oxides for superior sensitivity and tunable selectivity.