Inkjet-printed 2-D conductors for electromyography (EMG) electrodes in biosensing applications

Abstract

Graphene, a single sheet of carbon atoms arranged in a two-dimensional (2-D) honeycomb lattice extracted from bulk three-dimensional (3-D) graphite, has shown great promise towards low-profile sensing applications. Several studies have demonstrated its potential in acquiring 2-D electrophysiological measurements of the human body including the use of electromyography (EMG). Electromyograms require a minimum of two electrodes, making them a cost-effective option for the study of 2-D conductors interfaced to the human body. Although EMG signals are typically no more than 5 mV, they can be easily visualized through amplification with a gain resistor on a prototype circuit. In this study, preliminary EMG measurements of antagonist-agonist muscle pairs are collected through utilization of commercial electrodes to yield statistically significant results on the effect of gain on the Signal-to-Noise-Ratio (SNR) and on quantitative measurements of muscle force and associated amplitude. This information is then applied towards the exploration of producing graphene electrodes for biosensing. Presently, there have been limited studies on inkjet-printed electrodes for this purpose, with methods typically favoring screen-printing techniques. Therefore, there is value in analyzing reliable fabrication methods with graphene ink towards the production of devices for strain-dependent sensing and biosensing. To do this, graphene ink was processed via liquid-phase exfoliation with a mixture of graphite powder with typical solvents and other additives. This ink was printed on an SiO2/Si substrate to form electrodes for voltage testing in addition to electrode formation on flexible substrates for dynamic strain sensing. Here the conductivity was verified through strain-dependent testing, and the flexible graphene devices demonstrated live current changes at variable bending angles and in opposite profiles which we discuss in this work.