Highly stable potentiometric sensor with reduced graphene oxide aerogel as a solid contact for detection of nitrate and calcium ions

Abstract

• 3D reduced graphene oxide aerogel (rGOA) was synthesised through self-assembly of graphene oxide via heat treatment. • The sensor exhibited outstanding response, due to the large surface area and excellent electrical conductivity of rGOA. • Long-term stability of the sensor improved owing to the hydrophobicity of rGOA. • NO 3 – and Ca 2+ were detected in perilla leaves using the proposed sensor, and this result was in good agreement with the ICP and IC analysis results. Numerous reports have elucidated the importance of detecting of NO 3 − and Ca 2+ ions for monitoring their levels to optimize crop growth. Herein, we prepared a reduced graphene oxide aerogel (rGOA) as a promising solid-contact material for manufacturing a highly stable solid contact ion-selective electrode (SC-ISE) for monitoring to NO 3 − and Ca 2+ . The rGOA was synthesized through self-assembly of graphene oxide via heat treatment. Cyclic voltammetry and chronopotentilmetry were employed to demonstrate the fast charge transfer and large double layer capacitance of the rGOA layer modified electrode. The sensor comprising rGOA exhibited excellent Nernstian responses (59.1 mV/log [NO 3 − ] and 28.4 mV/log [Ca 2+ ]) and ion detection limits (759 nM for NO 3 − and 186 nM for Ca 2+ ) due to its outstanding electrical conductivity and large surface area of rGOA. The Ag/AgCl electrode with a polyvinyl butyral (PVB) film was used as the reference electrode. Water layer tests and potentiometry confirmed that the long-term stability of the electrode improved owing to the hydrophobicity of rGOA. Furthermore NO 3 − and Ca 2+ ions were detected in perilla leaf using the proposed ion-selective sensor, which was in agreement with the results of ion chromatography and inductively coupled plasma analyses. Thus, the proposed sensor provides an excellent sensing platform for the detection of inorganic ions in plant sap.