High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications

This paper presents development and performance assessment of an innovative and a highly potent graphene-electrolyte capacitive sensor (GECS) based on the supercapacitor model. Although graphene has been widely researched and adapted in supercapacitors as electrode material, this combination has not been applied in sensor technology. A low base capacitance, generally the impeding factor in capacitive sensors, is addressed by incorporating electric double layer capacitance in GECS, and a million-fold increase in base capacitance is achieved. The high base capacitance (∼22.0 μF) promises to solve many inherent issues pertaining to capacitive sensors. GECS is fabricated by using thermally reduced microwave exfoliated graphene oxide material to form interdigitated electrodes coated with solid-state electrolyte which forms the double layer capacitance. The capacitance response of GECS on subjecting to strain is examined and an enormous operating range (∼300 nF) is seen, which is the salient feature of this sensor. The GECS showed an impressive device sensitivity of 11.24 nF kPa-1 and good immunity towards noise i.e. lead capacitance and stray capacitance. Two regimes of operation are identified based on the procedure of device fabrication. The device can be applied to varied applications and one such biomedical application of breath pattern monitoring is demonstrated.