A cysteine sensor based on a gold nanoparticle-iron phthalocyanine modified graphite paste electrode

An electrochemical sensor for the sensitive and selective detection of cysteine is proposed based on a gold nanoparticle (AuNP)-iron(iii) phthalocyanine (FePc) modified graphite paste electrode. The sensor was characterised using scanning electron microscopy (SEM/EDX), transmission electron microscopy (TEM), cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry studies demonstrated that the electrochemical behaviour of cysteine at the AuNP-FePc modified graphite paste electrode is considerably improved compared to both the blank (unmodified) and FePc-modified graphite paste electrodes. The enhancement of the anodic redox signal for cysteine was due to a catalytic effect of gold nanoparticles which was investigated using three different graphite paste electrodes - 0.02, 0.055 and 0.11 wt% Au nanoparticles, each with a fixed quantity of FePc (5 wt%). The sensor fabricated using 0.055 wt% AuNPs exhibited optimum sensitivity as examined via differential pulse voltammetry measurements with an analytical range of 50-1000 μM and a LOD of 0.27 μM. The sensor was utilised for the determination of cysteine in pharmaceutical preparations.