Sensitive determination of caffeine by copper sulphide nanoparticles modified carbon paste electrode

• Starch assisted synthesis of CuS NPs by simple co-precipitation method in aqueous media.
• CuS NPs MCPE was used for caffeine sensor.
• CuS NPs MCPE exhibited better electrocatalytic activity towards the oxidation of caffeine.
• The electrokinetic rate of CuS NPs MCPE towards caffeine oxidation was found to be 2.174 × 103 s−1.
• The sensor showed lower detection limit, higher sensitivity and selectivity, wide linear range, good reproducibility and stability.

Copper sulphide nanoparticles (CuS NPs) were synthesized by simple co-precipitation method in aqueous media using starch as a biopolymer. The obtained product was characterized by XRD, SEM, EDX, TEM, FTIR and UV–vis techniques. The particle size was determined by TEM analysis and found to be in the range 20–50 nm. CuS NPs modified carbon paste electrode (CuS NPs MCPE) was employed to determine caffeine (CAF) by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The CuS NPs MCPE showed better electrocatalytic activity towards the oxidation of CAF, which was confirmed by enhance in the oxidation peak current and decrease in oxidation peak potential. Furthermore, in electrochemical impedance (EI) studies, the charge transfer resistance (RCT) at CuS NPs MCPE (12.1 kΩ) decreases as compared to bare CPE (42.6 kΩ), which suggests that CuS NPs improves the charge transfer capacity of CPE. Electron transfer kinetic parameters, sensitivity and surface active area of the electrode were determined. Under experimental conditions, the oxidation current of CAF was proportional to its concentration from 2 μM to 120 μM. The detection limit was found to be 18 × 10−9 M. The developed method was successfully applied to determine CAF content in food samples with appreciable results.