New Insight into the Mechanism of Simultaneous Determination of Ascorbic Acid, Dopamine, and Uric Acid with Graphene Encapsulated CoFe Alloys Electrochemical Sensor

Herein, a novel electrochemical biosensor is simply constructed by using graphene encapsulated CoFe alloy nanocomposite (CoFe@G) as the electrode modifier for highly sensitive and simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Cyclic voltammetry tests show well-separated peaks for AA at -7 mV, DA at 186 mV, and UA at 325 mV. CoFe@G modifier improves the differentiation of oxidative potential gap between AA and DA, realizing selective detection of these biomolecules. The mechanism of selective detection ability is studied by electrochemical impedance spectroscopy, quartz crystal microbalance (QCM), and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) analysis. It is demonstrated that modifying CoFe@G on glassy carbon electrode (GCE) can effectively lower the oxidation potential of AA other modifiers such as GCE and Au, avoiding potential overlapping with DA and UA and realizing well-resolved signals. QCM reveals that CoFe@G shows great improvement in adsorption of AA, which adsorbs on the graphene out layer in CoFe@G through C-H and C-O chemical bonding indicated by in situ ATR-SEIRAS analysis. It is experimentally demonstrated that both electron transfer and adsorption ability determine the external applied potential to trigger oxidation reaction, but adsorption ability is dominative.