Synthesis, structural characterization, and immunochromatographic application of a Hg–EDTA–BSA conjugate for mercury detection

Mercury contamination remains a global concern due to its bioaccumulation and high toxicity, posing severe environmental and health risks. Conventional analytical methods for Hg(II) detection, although sensitive, require costly instrumentation and complex sample preparation, limiting their use in field analysis. Immunochromatographic assays offer a rapid and user-friendly alternative. In our study, we report the synthesis, characterization, and immunochromatographic application of a novel mercury complex, Na₂ [HgEDTA], designed for selective detection of Hg(II) ions. The complex was obtained via direct coordination between HgCl₂ and Na₄EDTA in aqueous medium (1:1 M ratio) and characterized by FT-IR and XRD analyses, which confirmed the formation of a new crystalline phase and coordination of Hg²⁺ to the carboxylate groups of EDTA. UV–Vis spectroscopy in synthetic urine revealed a stable absorption band at 267 nm, indicating the compound's structural stability under biologically relevant conditions. The Hg–EDTA complex was subsequently conjugated to bovine serum albumin (BSA) to produce the immunogen Hg–EDTA–BSA, which served as the coating antigen in the immunochromatographic strip. Colloidal gold nanoparticles (AuNPs) synthesized via citrate reduction (λ_max = 530 nm) were successfully functionalized with monoclonal anti-Hg–EDTA antibodies, showing a bathochromic shift to 540 nm, confirming antibody adsorption. The assembled lateral flow immunoassay exhibited well-defined test and control lines, demonstrating specific antigen–antibody recognition and efficient capillary migration. These results validate the synthesis and structural integrity of the Hg–EDTA–BSA conjugate and confirm its applicability as a stable and sensitive platform for rapid colorimetric detection of mercury ions.