The Ultra-sensitive Electrochemical Detection of As(III) in Ground Water Using Disposable L-cysteine/Lipoic Acid Functionalised Gold Nanoparticle Modified Screen-Printed Electrodes

Abstract

An ultrasensitive electrochemical sensor to detect arsenic (III), a highly toxic heavy metal ion, has been successfully developed. The sensing platform composed of L-cysteine (Lcyst) molecules conjugated to reduced lipoic acid (rLA) capped gold nanoparticles and exhibited an indirect band gap energy (Eg) of 1.96 eV. This is a characteristic of a semiconducting material; metals and semiconducting nanomaterials possess good electrochemical properties due to their trivial band gap energies. Surface ligation of the gold nanoparticles with rLA and Lcyst did not only prevent the nanoparticle agglomeration but also improved the susceptibility of the sensor to bind efficiently to heavy metal ions of interest. The electrochemical properties of the sensing platform were demonstrated by a reversible redox electron transfer reaction of the gold oxides due to the presence of gold nanoparticle clusters on the screen-printed carbon electrode surface. The sensor parameters such as the scan rate, pH and the deposition potential were optimised. The sensor was capable of detecting the arsenic (III) ions at the formal peak potential (Epa°′) of −0.307 ± 0.02 V. Subsequently, the sensor demonstrated a low limit of detection with the magnitude of 3 ppb (i.e. 3SD/SLOPE). The dynamic linear range of the developed sensing platform was between 3 and 25 ppb. The sensor was used to detect As(III) in ground water and demonstrated excellent recoveries in spiked samples. The AuNP-rLA-Lcyst sensing platform fabricated for the detection of As(III) heavy metal ion using the square-wave anodic stripping voltammetry.