Highly sensitive voltammetric sensor comprising CuSn(OH)₆–multi-walled carbon nanotubes–β-cyclodextrin composites and poly(L-arginine) for indole-3-lactic acid analyses in alcohol use disorder serum samples

A highly sensitive voltammetric sensing platform configured via the drop-casting of composites of CuSn(OH)₆–multi-walled carbon nanotubes–β-cyclodextrin (CuSn(OH)₆–MWCNT–βCD) on an arginine-electropolymerized screen-printed carbon electrode (CuSn(OH)₆–MWCNT–βCD/p-Arg/SPCE) was demonstrated to determine the concentrations of indole-3-lactic acid (ILA) in buffer and serum solutions. Prior to the analysis, the successful assembly of the composites and polymer layers was confirmed using field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The changes in the current due to the direct oxidation of ILA on the modified electrode were used to quantify the ILA. A dynamic range of 0.05–20 μM with a limit of detection of 9 nM for ILA under optimal conditions was achieved primarily with the combined use of CuSn(OH)₆, MWCNT, and βCD, resulting in a large electrochemical active surface area (0.185 cm²), low charge transfer resistance (∼2 Ω), and fast electron transfer. Furthermore, the sensing performance, including selectivity, sensitivity, reproducibility, repeatability, and stability, for ILA detection was evaluated. Finally, the ILA concentrations in the pooled clinical serum samples of healthy control and alcohol use disorder patients were measured using our method, the results of which exhibited a notable resemblance to those obtained using liquid chromatography with tandem mass spectrometry.