Inkjet printing of Pd/SO₃H-modified graphene on different polymeric substrates to construct flexible electrochemical sensors

The hydrophilic nature of sulfonated (SO3H) graphene was exploited to prepare aqueous inks with high concentrations and the development of disposable, flexible, and enzyme-free electrochemical glucose sensors is described. The inks were printed on the flexible substrates using inkjet printing method. Different polymeric flexible substrates, polyethylene terephthalate (PET) film, and polypropylene-based crystal clear A4 folder (CCF) were used as substrates. Micron-scale (similar to 4 mu m) electrode thickness with an average surface roughness of 14 nm was obtained. The changes in the sheet resistances of Pd/SO3H-rGO@PET and Pd/ SO3H-rGO@CCF after bending cycles were found to be 6.8% and 2.0%, respectively, confirming the high bending resistance of the deposited layers. The results showed that developed flexible sensors showed high electrocatalytic activities against glucose. Furthermore, CCF-based flexible sensors showed higher sensitivity [y (nA) = 0.52x (mM) + 12.15) with a wider linear range of 1-20 mM compared to PET-based sensors.