Flexible strain sensors have attracted a lot of interest lately, especially in the field of wearable sensors, electronic skin and soft robotics. They are conformable, making them easy to use, and cause minimum discomfort. There is thus a huge demand for highly sensitive, fast-responding, flexible piezoresistive materials that can be used in wearable sensors and point-of-care diagnostic instruments. The most common approach toward developing such materials is adding conductive fillers to elastomeric polymers, the sensitivity of which depends on the filler concentration and homogeneity of the composite, resulting in variations in properties and making them complex to fabricate. Here, we present the fabrication and application of a flexible, conformable, thin piezoresistive sensor design that can be used for pressure sensing in electronic skin application.

Highly exfoliated graphene oxide (GO) solution in de-ionized water was initially synthesized using the the modified Hummers method. Lint-free tissue paper (Kimberly Clark make) was soaked in the GO solution and dried several times to obtain a good network of GO in the paper. This was then attached to a partially cured PDMS layer for mechanical stability. The GO was further reduced to rGO using a 450 nm laser by optimizing the intensity. This laser-reduced rGO was placed on interdigitated electrodes to make the sensor.

A 40% change in sensitivity was observed for a 60 kPa pressure when tested using a Keysight source meter. The thickness of the sensor was found to be less than 700 micron, hence making it possible to use for electronic skin applications