There is a strong commercial need for inexpensive point-of-use sensors for monitoring disease biomarkers or environmental contaminants in drinking water. Point-of-use sensors that employ smart polymer hydrogels as recognition elements can be tailored to detect almost any target analyte, but often suffer from long response times. Hence, we describe here a fabrication process that can be used to manufacture low-cost point-of-use hydrogel-based microfluidics sensors with short response times. In this process, mask-templated UV photopolymerization is used to produce arrays of smart hydrogel pillars inside sub-millimeter channels located upon microfluidics devices. When these pillars contact aqueous solutions containing a target analyte, they swell or shrink, thereby changing the resistance of the microfluidic channel to ionic current flow when a small bias voltage is applied to the system. Hence resistance measurements can be used to transduce hydrogel swelling changes into electrical signals. The only instrumentation required is a simple portable potentiostat that can be operated using a smartphone or a laptop, thus making the system suitable for point of use. Rapid hydrogel response rate is achieved by fabricating arrays of smart hydrogels that have large surface area-to-volume ratios.

This paper reports the development of a nano-gap vapor sensor that is capable of detecting an airborne target in a repeatable manner in near-zero static power consumption. The nano-gap sensor employed a matching gap distance of 5.8 nm to the lengths of both linkers and targets for selectivity. The nano-gap sensor was fabricated based on deposition and removal of a thin sacrificial layer via atomic-layer-deposition (ALD), and then coated with newly-synthesized linkers. The fabricated vapor sensor demonstrated the detection of a target gas (1, 5-Diaminopentane) or Cadaverine in a concentration of <;100ppm; produced a notable on/off current ratio of 10⁴~10⁷; and repeatable performance up to 2 times.

Functionalized engineered nanogap electrodes (pair of electrodes separated by a gap of a few nanometers) are utilized as tunneling chemoresistors for gas sensing and resistance switching at the molecular scale. The nanogap device consists of two gold electrodes vertically separated by a very thin spacer of 2 nm of α-Si and ~4 nm of dielectric (SiO ₂ or Al ₂ O ₃ ). A ~10 nm wide sidewall air gap is formed by etching the spacer along the edge of the electrodes followed by linker functionalization. After exposure to a gaseous chemical target (1,5-Diaminopentane), the target gas molecules adsorb onto the linker-coated surface bridging the two electrodes and establish an electrically conductive path. Preliminary electrical measurements indicate a nearly reversible decrease of electrical resistance between five to seven orders of magnitude when exposed to the target. The large change in resistance and the high value of resistance in air makes this device suitable as a candidate for a gas-triggered on-off switch with pW standby power consumption.

Smart hydrogels are inherently biocompatible hydrophilic three-dimensional polymer networks able to undergo a volume-phase transition in the presence of an analyte. By molecular imprinting and/or aptamer-based approaches they can be tailored for a wide range of analytes with high selectivity. In combination with the biocompatibility, this makes hydrogels very promising candidates for biomedical sensor applications. However, to date hydrogels are rarely used for that purpose as the reliable detection of their swelling state remains a challenge. Here we report on a newly developed biocompatible bending sensor platform which can be equipped with almost any smart hydrogel, thereby paving the way for biomedical applications.