Highly sensitive and selective electrochemical detection of caffeine, theophylline and guaiacol in green tea, green coffee, coffee, and tea extracts using a SnS2 nanoflake-modified electrode

Abstract

SnS₂ (TS) nanostructures with different morphologies were synthesized in three different solvents, Milli-Q water (W), ethanol (E) and isopropanol (I), using a simple solvothermal method. The phase, morphology and molecular structure of the synthesized TS nanostructures were investigated through powder X-ray diffraction, FE-SEM (field emission scanning electron microscopy), high-resolution TEM and XPS analysis. The synthesized TS nanostructure electrocatalysts were applied for the detection of caffeine (CFN), theophylline (THN) and guaiacol (GCL). During this study, we used methods such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The TS(I)-modified glassy carbon electrode [TS(I)@GCE] showed superior sensitivity towards CFN, THN and GCL. Its electrochemical linearity range was found to be 0.10–0.27, 0.01–0.25 and 0.1–0.20 μM with detection limits of 6.71, 4.0 and 11.2 nM for CFN, THN and GCL, respectively; electrochemical sensitivity was found to be 190.20 μA μM⁻¹ cm⁻², 84.72 μA μM⁻¹ cm⁻² and 50.32 μA μM⁻¹ cm⁻², respectively. The calculated recyclability and long-term storage stability confirmed the robustness of the TS(I)@GCE electrode-based sensor. The detection of CFN, THN and GCL in the presence of dopamine (DPN) as well as in real green coffee, coffee, green tea, and tea samples validated the analytical performance of TS(I)@GCE for the precise and simultaneous detection of biomolecules. To the best of our knowledge, this is the first study on the simultaneous electrochemical detection of CFN, THN and GCL via a TS electrocatalyst. The resultant concentration of the analyte was verified through the spiking method. Consequently, the obtained data varies and represents good contact for the detection of caffeine, theophylline and guaiacol in real samples.