Simultaneous colorimetric and electrochemical detection of trace mercury (Hg2+) using a portable and miniaturized aptasensor

Authors: ULLO, A - Purdue University; LUCAS, A - Purdue University; KONERU, A - Purdue University; BARUI, A - Purdue University; STANCIU, L - Purdue University

Submitted to: Biosensors and Bioelectronics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2022
Publication Date: N/A
Citation: N/A
DOI: https://doi.org/10.1016/j.bios.2022.114419

Interpretive Summary: Mercury is a heavy metal toxic to a number of human organ systems and, according to the World Health Organization, elemental mercury vaporizes readily, and it can stay for up to a year in the atmosphere until it ultimately settles in the sediment of water bodies. Available analytical methods for detection of mercury in environmental samples have remarkable sensitivity and selectivity, but are complex lab-based methods, require extensive sample preparation, trained personnel, and are unsuitable for on-site detection. To overcome these problems, we developed a color-changing and electrochemical biosensor to allow user-friendly, rapid, and sensitive portable testing for detection of mercury from water samples. The biosensor was designed to avoid false-positive/false-negative results and to support future commercialization efforts. The development of this dual-mode platform opens the way to the future development of multiplexed paper-based sensors for the detection of heavy metals, toxins, or pathogens for on-site applications.

Technical Abstract: We report a novel aptasensor for the simultaneous colorimetric and electrochemical detection of mercury (Hg2+). 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 Hg2+ down to 0.01 ppm based on 3s of the blank/slope criteria. Moreover, it is highly selective against As2+, Cu2+, Zn2+, Pb2+, Cd2+, Mg2+, and Fe2+, 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 R2= 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 (NH3)6]3+Cl3] redox probe. The latest component presents a linear range from 0.01 to 1 ppm (adjusted R2= 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.