Abstract

Two selective methods were developed for detecting mercury ions (Hg²⁺) in food and water samples using catalytic fluorometry based on Au-Hg amalgamation with enhanced peroxidase-like activity. These approaches include (i) a laser-printed microfluidic paper-based analytical device (LP-µPAD) and (ii) a paper-based microcentrifuge tube test kit. The LP-µPAD was fabricated via commercial laser printing and integrated gold nanoparticles (AuNPs) with o-phenylenediamine (OPD) and hydrogen peroxide (H₂O₂). The test kit enabled Hg²⁺ detection in food by reducing Hg²⁺ to Hg⁰ with stannous chloride, facilitating Au-Hg amalgam formation in the detection zone. Both approaches utilized the Au-Hg amalgam to catalyze H₂O₂-mediated oxidation of OPD, generating fluorescent 2,3-diaminophenazine (DAP), further enhancing fluorescence intensity in proportion to Hg²⁺ concentrations. The LP-µPAD exhibited a detection range of 3.0–20.0 µg L⁻¹ with a limit of detection (LOD) of 1.65 µg L⁻¹, whereas the test kit provided a detection range of 0.1–1.0 mg L⁻¹ with an LOD of 0.08 mg L⁻¹. Both sensors showed high selectivity for Hg²⁺ over other ions and performed well in real sample analyses, aligning closely with results from conventional methods.