Fabrication and comprehensive comparison of the performance of chemically modified GCE and SPCE for the simultaneous determination of uric acid and vanillylmandelic acid

Uric acid (UA) and Vanillylmandelic acid (VMA) are two important biomarkers that can significantly account for certain pathological conditions in our body. A novel and efficient electrochemical sensor has been fabricated for the simultaneous determination of UA and VMA based on screen printed carbon electrodes chemically modified with a nanocomposite of reduced graphene oxide and poly(L-threonine) conducting polymer (rGO- p(Thr)/SPCE). The fabricated sensor has been well characterized and various experimental conditions were optimized to avail maximum performance of the sensor towards the determination of UA and VMA. In addition, the sensor's performance was rationally analysed and compared with the same sensor fabricated on a conventional glassy carbon electrode (rGO- p(Thr)/GCE) to understand how the change in electrode substrate affects the sensor's performance. Studies revealed that although both of the sensors can be successfully applied for the simultaneous determination of UA and VMA over wide linear ranges with lower detection limits, better sensitivity was acquired when rGO- p(Thr)/GCE was used. On the other hand, modification of SPCE provided greater reduction in electrooxidation potential of UA and VMA than GCE. Electroactive surface area changes in GCE and SPCE upon modification showed different trends, whereas study on mechanistic aspects of electrooxidation exhibited similar results. Since SPCE is more of practical relevance considering the ease of miniaturization and applicability in on-site analysis, studies on interference by probable coexisting species and applicability of the sensor in synthetic physiological fluids were also successfully carried out on rGO-p(Thr)/SPCE.