Thiol-functionalized reduced graphene oxide as self-assembled ion-to-electron transducer for durable solid-contact ion-selective electrodes

Thiol-functionalized reduced graphene oxide (TRGO) as a novel ion-to-electron transducing layer is firstly employed to develop durable solid-contact ion-selective electrodes (SC-ISEs) in this work. The performance of the sensors is evaluated by determining K⁺ and NO₃ ⁻ as an example of cation and anion. The covalent linkage of TRGO at golden electrode surface generates a stable transducing layer. No water films are observed in the proposed TRGO-based potassium (K⁺-TRGO-ISEs) and nitrate (NO₃ ⁻-TRGO-ISEs) selective SC-ISEs. The resultant electrodes exhibit Nernstian responses (60.0 ± 0.4 mV/decade for K⁺-TRGO-ISEs and −60.0 ± 0.5 mV/decade for NO₃ ⁻-TRGO-ISEs), low detection limits (2.5 × 10⁻⁶ M for K⁺-TRGO-ISEs and 4.0 × 10⁻⁶ M for NO₃ ⁻-TRGO-ISEs) and good selectivity behavior. More importantly, the TRGO-based SC-ISEs display a much longer lifetime of 2 weeks than that of reduced graphene oxide-based SC-ISEs in continuous flowing solutions using a longer peristaltic pump. These improvements push TRGO a general and reliable transducer for the development of durable SC-ISEs.