With its all-surface 2D structure combined with very high carrier mobility, graphene is an extremely promising candidate for high sensitivity and low noise chemical sensing ^{[1] [2]} . Graphene devices can perform electrical detection for chemical sensing in many applications, e.g.,pH monitoring in electrolytes ^{[3] [4]} , measuring blood glucose, and in-vitro recording of the electrical activity of living cells ^[5] . Integrating graphene on plastic substrates ^[6] enables fabrication of low-cost, flexible sensors.

Our group has developed the first solution-gated graphene field effect transistor (SGFET) on a polyethylene naphthalate (PEN) substrate. These devices have important advantages with respect to traditional sensors, e.g., intrinsic signal amplification, simple electronic read-out, and straightforward integration with microelectronics. Fabrication of the SGFET starts with the transferring of graphene grown by chemical vapor deposition on the PEN substrate. Metal contacts were previously evaporated on the PEN substrate. Silicone rubber-based insulation was used to protect the metal contacts and wires from any contact with the electrolyte.

As Figure 2.a) shows, the characterization of our devices in a phosphate buffer solution demonstrates good transconductance, around 1 mS.mm^-1, and carrier mobility of 300 cm².V^-1.s^-1. Transconductance is 5 times smaller than that obtained for graphene on SiO₂ which is due to the 10 times rougher surface of PEN compared to SiO₂ and also the larger amount of PMMA residues remaining on graphene when transferred onto PEN. The pH measurements have been performed using these devices by recording how the Dirac point shifts with changes in pH, as Figure 2.b) shows. Sensitivity  to 22 mV/pH has been demonstrated. In addition, long-term pH monitoring was shown for the first time in these graphene devices, as Figure 2.c) shows. Our on-going work focuses on functionalizing graphene to demonstrate new biosensors for glucose and E. coli detection on plastic substrate.

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