Simultaneous colorimetric and electrochemical detection of trace mercury (Hg 2+ ) using a portable and miniaturized aptasensor.

We report a novel aptasensor for the simultaneous colorimetric and electrochemical detection of mercury (Hg). This device consists of a paper-based microfluidic component (μ-PAD) incorporated into a miniaturized three-electrode system fabricated through printed circuit board (PCB) technology. This biosensor is portable, rapid, versatile, and can detect Hg down to 0.01 ppm based on 3σ of the blank/slope criteria. Moreover, it is highly selective against As, Cu, Zn, Pb, Cd, Mg, and Fe, reaching up to 13 times more of the input signal than the other heavy metals. The colorimetric detection mechanism uses aptamer functionalized polystyrene (PS)-AgNPs and Ps-AuNPs microparticles' specific aggregation. The Ps-AuNPs-based system allows qualitative detection (LOD 5 ppm) and stability over seven days (up to 97.59% signal retention). For the Ps-AgNPs-based system, the detection limit is 0.5 ppm with a linear range from 0.5 to 20 ppm (adjusted R= 0.986) and stability over 30 days (up to 94.95% signal retention). The electrochemical component measures changes in charge transfer resistance upon target-aptamer hybridization using a [Ru (NH)]Cl] redox probe. The latest component presents a linear range from 0.01 to 1 ppm (adjusted R= 0.935) with a LOD of 0.01 ppm and performance stability over seven days (up to 102.52 ± 11.7 signal retention). This device offers a universal dual detection platform with multiplexing, multi-replication, quantitative color analysis, and minimization of false results. Furthermore, detection results in river samples showed recoveries up to 91.12% (RSD 0.85) and 105.61% (RSD 1.62) for the electrochemical and colorimetric components, respectively. The proposed system is highly selective with no false-positive or false-negative results in an overall wide linear range and can safeguard the accuracy of detection results in aptasensing platforms in general.