Colorimetric and amperometric detection of urine creatinine based on the ABTS radical cation modified electrode

In this contribution, we examined and applied the redox chemistry of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cations (ABTS^•+) with creatinine for the colorimetric and amperometric detection of urine creatinine. Colorimetric studies reveal that ABTS^•+ is reduced and decololorized in the presence of creatinine, and its initial reaction rate is proportional to the initial concentrations of both ABTS^•+ and creatinine. A colorimetric creatinine sensor was developed by entrapping ABTS into a chitosan film modified FTO substrate, followed by integrating a Nafion® overlayer to minimize the interferences from negative-charged biomolecules in urine, and applying an anodic pretreatment to generate ABTS^•+. The developed colorimetric sensor exhibits promising sensing characteristics, including high accuracy for the detection creatinine in neat urine. On the other hand, the electrocatalytic scheme involving the electrochemical generation of ABTS^•+ and reduction of ABTS^•+ by creatinine forms the basis for the amperometric detection of urine creatinine. The developed electrochemical creatinine sensor, consisting of a Nafion® coated ABTS-CNT nanocomposite, also exhibits promising sensing characteristics, including high sensitivity (27.3 ± 0.5 μA cm^-2 mM^-1), low detection limit (∼11.0 μM), wide linear range (upto 21.3 mM), fast response time (t₉₅) (<60 s), and high accuracy for the detection of urine creatinine.