Hydrothermally reduced graphene oxide as a sensing material for electrically transduced pH sensors

A reagent-less sensing probe has been developed using hydrothermally reduced graphene oxide (HRGO) and investigated as potentiometric and chemiresistive pH sensor. The HRGO modified electrode, used as a potentiometric sensing probe, showed a sensitivity of 66 mV / pH for a freshly prepared electrode. After a few exposures to different buffers, a stable sensitivity of 55 mV / pH was obtained in a pH range from 2 to 12. In the chemiresistive sensing mode, the HRGO electrode showed a sensitivity of around 44 omega / pH in a pH range from 4 to 7. The results showed that the HRGO modified electrode could be used as a potentiometric pH sensor and as a chemiresistive sensor. However, the chemiresistive sensor has a narrow working pH range of 4-7 compared to the potentiometric sensing method. The chemiresistive sensor has a good sensitivity between pH 4 and 7 and may be used to measure pH in some biological processes. The electrochemical nature of HRGO surface functionalities was explored by cyclic voltammetry. The presence of a quinone-like redox couple was identified on the HRGO surface. The redox activity of these functional groups was studied at different pH. Further, the quinone-like moieties were confirmed by their electrocatalytic activity towards dissolved oxygen.