A Sensor for Electrochemical pH Monitoring Based on Laser-Induced Graphene Modified with Polyfolate

A laser-induced graphene (LIG) modified with chitosan (Chit) and conducting polymer polyfolate (PFA) was used as a base to develop a flat and flexible pH sensor. LIGs were formed using two different irradiation wavelengths of 355 nm and 532 nm. Depending on the wavelengths, the obtained electrodes were named LIG355 and LIG532. Microscopic imaging revealed that the bare LIG electrode surface had rough structures after laser treatment giving hydrophilic properties, and that PFA forms fibre-like structures on Chit coated LIG. Electrochemical investigation with the redox probe demonstrated that diffusion is a limiting process at the bare and modified LIG electrodes. A capacitive behaviour was observed from electrochemical impedance spectra at bare electrodes, showing a rather rough interface at LIG355 but a microporous one at LIG532. The developed flat and flexible electrode was sensitive to pH in the region from 6.0 to 9.0. In the studied pH range, the sensitivity was 27.86 & PLUSMN; 0.81 for PFA/Chit/LIG355 and 30.32 & PLUSMN; 0.50 mV/pH for PFA/Chit/LIG532 with moderate stability for a period of more than two months.