In this paper, we investigated the effect of humidity on paper substrates and propose a simple and low-cost method for their passivation using ZnO nanoparticles. To this end, we built paper-based microdevices based on an interdigitated electrode (IDE) configuration by means of a mask-less laser patterning method on simple commercial printing papers. Initial resistive measurements indicate that a paper substrate with a porous surface can be used as a cost-effective, sensitive and disposable humidity sensor in the 20% to 70% relative humidity (RH) range. Successive spin-coated layers of ZnO nanoparticles then, control the effect of humidity. Using this approach, the sensors become passive to relative humidity changes, paving the way to the development of ZnO-based gas sensors on paper substrates insensitive to humidity.

Wearable biosensors for the detection of analytes in sweat are an emerging and promising technology with important applications in monitoring a person’s physiological state. Sweat, being an easily accessible biofluid, shows great potential as a biological fluid for wearable devices, but also a number of challenges that must be addressed before a sensor can be commercialized. As an example, sensor fabrication on flexible substrates can greatly affect the performance of the device. Herein, the development of an enzymatic electrochemical sensor on a flexible substrate for glucose detection is presented. The sensor’s three-electrode systems were made entirely with carbon-based ink on polyimide substrates and decorated with carbon black. The developed and optimized sensor design exhibited a stable and reproducible performance and was able to detect glucose in concentrations relevant to the ones present in sweat.