Label-free and simple detection of trace Pb(II) in tap water using non-faradaic impedimetric sensors

This article describes a simple non-faradaic impedimetric sensor comprised of L-Cysteine self-assembled on top of an interdigitated gold electrode for the direct detection of lead ions (Pb(II)) in tap water. The sensor consists of only two electrodes and does not require redox probe during detection. During the detection of Pb(II) in tap water, changes in capacitance were observed with a sensitivity of 9.4 nF/log(nM) and a limit of detection of 45 pM at a biasing frequency as low as 10 Hz, which is well below the World Health Organization WHO recommendation for Pb(II). The sensor demonstrated satisfactory selectivity toward Pb(II) in comparison to Sn(II), Zn(II), Cu(II), Na(II), Mg(II) and Ca(II). In addition, the system allows a wide working frequency window up to similar to 5 kHz, for which higher sensitivities can still be obtained. ATR-FTIR spectrum confirmed the functionalization of L-Cysteine onto interdigitated gold electrodes. Fur-thermore, XPS results confirmed complete thiolate-gold bonding, with no adsorbed sulfur or unbound thiol between L-Cysteine and the electrode surface. Also, the binding of Pb(II) to L-Cysteine was con-firmed by XPS to take place mainly through the carboxyl group. The reported method is promising for constructing miniaturized sensors for the direct detection of Pb(II) in low-volume tap water samples. (c) 2021 Elsevier B.V. All rights reserved.