An rGO-modified all-solid-state tetracaine-selective microsensor with enhanced interfacial stability for rapid...

An all-solid-state tetracaine-selective microsensor with enhanced interfacial stability was developed for rapid potentiometric determination of tetracaine in ophthalmic formulations. The sensor was fabricated by depositing a reduced graphene oxide (rGO) ion-to-electron transducing layer onto a glassy carbon substrate, followed by coating with a poly(vinyl chloride)-based ion-selective membrane incorporating tetracaine-tetraphenylborate (TC/TPB) as the electroactive ion-association complex. A corresponding unmodified sensor was fabricated for comparative evaluation. The optimized rGO-modified microsensor exhibited a near-Nernstian slope of 59.1 ± 0.7 mV per decade over the concentration range of 1.0 × 10^-6-1.0 × 10^-1 mol L^-1, with a detection limit of 5.49 × 10^-7 mol L^-1 and rapid response characteristics. Compared with the unmodified electrode, the rGO-modified sensor demonstrated superior potential stability, improved electrode-to-electrode reproducibility, and significantly enhanced interfacial charge-transfer behavior. Water-layer and chronopotentiometric studies confirmed the beneficial role of rGO in suppressing water-layer formation and improving ion-to-electron transduction at the membrane/substrate interface. The microsensor also exhibited excellent selectivity toward tetracaine over common inorganic ions, structurally related compounds, and pharmaceutical excipients, with stable operation across the pH range 4.0-7.0. Application to commercial ophthalmic formulations afforded recoveries between 98.6 and 101.6%, in close agreement with a reference UV-vis spectrophotometric method. The developed microsensor provides a simple, rapid, and cost-effective analytical platform for tetracaine determination and demonstrates the effectiveness of graphene-based solid-contact transducers in improving the performance of pharmaceutical potentiometric microsensors.