Herein, we present a greener approach to achieve an ultrasensitive,
selective, and viable sensor engineered by amino acids as a recognition
layer for simultaneous electrochemical sensing of toxic heavy metals
(HMs). Electrochemical techniques like electrochemical impedance spectroscopy
(EIS), cyclic voltammetry (CV), and square-wave anodic stripping voltammetry
(SWASV) were applied to demonstrate sensing capabilities of the designed
analytical tool. The comparative results of different amino acids
demonstrate alanine’s superior performance with a well-resolved
and enhanced current signal for target metal ions due to strong complexation
of its functional moieties. The working conditions for alanine-modified
GCE were optimized by investigating the effect of alanine concentration,
different supporting electrolytes, pH values, accumulation potentials,
and time. The limits of detection
for Zn2+, Cd2+, Cu2+, and Hg2+ were found to be 8.92, 5.77, 3.01, and 5.89 pM, respectively.
The alanine-modified electrode revealed absolute discrimination ability,
stability, and ultrasensitivity toward metal ions even in the presence
of multifold interfering species. Likewise, greener modifier-designed
electrodes possessed remarkable electrocatalytic activity, cost affordability,
reproducibility, and applicability for picomolar level detection of
HM ions in real water sample matrixes. Theoretical calculations for
the HM–amino acid interaction also support a significantly
improved mediator role of the alanine modifier that is consistent
with the experimental findings.