A Dicysteinyl Tripeptide-Based Electrochemical Sensor for Highly Selective and Stable Detection of Mercury(II) Ions

Abstract

Global industrialization has made it necessary to create cheap, quick ways to measure mercury(II) ions (Hg2+) in water systems. This study presents a dicysteinyl tripeptide of NH2-Cysteine-Alanine-Cysteine-COOH (CAC)- based electrochemical sensor designed for the highly selective and stable detection of Hg2+ ions. The modified electrode was fabricated by the immobilization of the CAC-tripeptide and multi-walled carbon nanotubes (MWNTs) within a Nafion polymer matrix onto a platinum electrode (Pt). Molecular dynamics (MD) simulations confirmed that Hg2+ chelation via dicysteinyl thiol groups rigidifies the CAC tripeptide matrix into a structurally stable, low-flexibility conformation. This CAC/MWNTs/Nafion/Pt electrode modification provided a high surface area and superior charge transport capacity, resulting in good sensitivity. Analytical validation demonstrated a linear response range of 10 to 100 nM, with a limit of detection (LOD) of 7.9 nM, effectively exceeding the World Health Organization (WHO) safety criterion of 10 nM. With a relative standard deviation (RSD) of 3.1% (n = 7) at 100 nM Hg2+, the modified electrode demonstrated great precision. Moreover, the biosensor exhibited excellent reproducibility and substantial long-term stability, maintaining 85% of its initial electrochemical response after a three-week duration. Selectivity studies showed that most species were quite resistant to competing metal ions, with only Cu2+ and Ag+ causing modest problems. Based on this result, the immobilization of the CAC-tripeptide and multi-walled carbon nanotubes (MWNTs) within a Nafion polymer matrix onto a platinum electrode development seems like a promising early, easily accessible option for environmental water quality monitoring in real time.