An electrochemical sensor for caffeine at a carbon nanofiber modified glassy carbon electrode

This study demonstrates the electrochemical behaviour of caffeine on an acid activated carbon nanofiber (CNF) modified glassy carbon electrode (GCE) using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) techniques. Characterization of the bare and CNF modified GCE was performed using a [Fe(CN)₆]^−3/−4 redox probe and caffeine in 0.1 M H₂SO₄. The fabrication of the electrochemical sensor was achieved simply by drop-coating the surface of GCE with CNF solution. The pristine and acid activated CNFs was characterized by electron microscopy, FTIR, Raman spectroscopy and X-ray diffraction spectroscopy. The presence CNF modifier increased the rate of electrochemical reaction, favoured the electro-oxidation of caffeine at 1.35 V in comparison to oxidation at the bare which occurred at 1.44 V, and caused a 2.35-fold current increase for caffeine at CNF modified GCE. SWV was performed in a concentration range from 25 to 450 µM and the sensor obtained a limit of detection of 17.40 µM. The proposed method was successfully validated by UV–Vis spectroscopy. This sensor lends itself to the detection of caffeine in pharmaceutical, food and beverage samples.