A selective voltammetric pH sensor using graphitized mesoporous carbon/polyaniline hybrid system

Development of a new pH sensor system, which is simple to prepare, sensitive, selective and workable with low volume, is demanding research in biomedical and environmental studies. In the literature, organic molecules like methylene blue, toluidine blue, hydroquinone, catechol, anthraquinone and polyaniline-based redox probes have been widely used for this purpose. In general, these redox probes have easily interfered with common biochemicals such as dopamine, ascorbic acid, NADH, H2O2, cysteine, hydrazine, and some transition metal ions, etc., and in turn to marked potential and current drifts (pH-false positive response). In this work, a highly redox-active, stable and interference-free redox polymer based on poly(4-chloroaniline) (PANI(4-Cl)) modified graphitized mesoporous carbon (GMC), designated as GMC@PANI(4-Cl), has been prepared using 4-chloroaniline as a monomer in pH 7 phosphate buffer solution. The new redox polymer system showed a distinct redox peak at Eo’= 0.15 V vs Ag/AgCl with a stable voltammetric response. Transmission electron microscope analysis of the redox polymer composite had shown adhesion of black polymeric solid due to polyaniline like the molecular system as a surface layer on the GMC material. The constructed calibration plot was linear in the pH window 2-11 with a slope and regression values − 58 mV pH−1 and 0.9997, respectively. The GMC@PANI(4-Cl) modified electrode showed a sensitive and selective pH monitoring without any interference from the common biochemicals as listed above. As a practical application, pH sensing of commercial pH solutions, undiluted urine and saliva samples were demonstrated. Also, a three-in-one screen-printed carbon modified GMC@PANI(4-Cl) was explored for pH monitoring of a bacterial (E.coli) growth, which showed a comparable response with the conventional pH electrode.