One-pot electrosynthesis of silver nanorods/graphene nanocomposite using 4-sulphocalix [4] arene for selective detection of oxalic acid

Oxalic acid (OA) is present in various plants, animals and microorganisms. Abnormal levels of OA could remove Ca2+ from blood and form less soluble salts in the digestive system which can lead to kidney stones. So, it is very important to accurately measure the OA concentration in various samples for medical diagnosis and controlling renal stone formation. In this study, we reported an electrochemical synthesis of graphene (Gr) functionalized with silver nanorods (Ag NRs) using 3D surfactant 4-sulphocalix[4]arene (SCX) and silver nitrate (AgNO3) from an aqueous solution. SCX is acted as a soft template to form Ag NRs along with the Gr sheets. UV-visible (UV-vis), Fourier-transform infrared (FT-IR) and Raman spectroscopies have confirmed the formation of Gr with Ag NRs. In order to develop a selective electrochemical sensor for OA, Gr-Ag NRs nanocomposite coated glassy carbon electrode (GCE) was prepared and tested for OA oxidation. This new sensor (Gr-Ag NRs/GCE) exhibited high catalytic activity for OA in 0.1 M phosphate buffer and it showed a linear detection of OA from 3 to 30 mM with a detection limit of 0.04 mM. The effect of scan rate, pH and amount of catalysts were optimized. The interference of metal ions (Mg2+, Ca2+, Zn2+, Ni2+ and Co2+) and biomolecules such as ascorbic acid (AA) and uric acid (UA) were tested. Gr-Ag NRs/GCE is selectively responded to OA in the presences of these interferent ions. Moreover, the Gr-Ag NRs nanocomposite based sensor was successfully applied to detect OA in tap water samples with recoveries of 100 to 102%.