Simple Photothermal Paper-Based Analytical Device Using Silver Nanomaterials for Quantitative Mercury Ion Monitoring in Drinking Water and Wolffia Samples

Abstract

Herein, we present a sensitive and straightforward photothermal-based paper analytical device (PT-PAD) for quantifying mercury ions (Hg2+) in drinking water and Wolffia samples, facilitating rapid screening of the aquatic plant's quality in association with environmental water. The technique involves the etching reaction of silver nanoparticles (AgNPs) with Hg2+ on the paper substrate, which leads to a change in their photothermal conversion. The Hg2+ levels can be achieved by monitoring the temperature change under the irradiation with a 405 nm laser pointer. The sensor established the working linear range between 3.0 and 11.0 ppb with the detection limit (LOD) of 0.06 ppb. Furthermore, it offers remarkable precision with a maximum relative standard deviation (RSD) of 7.3%. Likewise, there were no significant interference effects from both anions and cations, indicating a high selectivity for Hg2+ monitoring. The proposed method exhibits excellent accuracy and precision for detecting Hg2+ levels in drinking water and Wolffia samples, with a recovery range of 96.0-104.0% and a highest RSD of 4.4%. These results are compatible with an inductively coupled plasma mass spectrometry (ICP-MS) method. Despite not using complex instruments, the assay shows a greater detection performance compared to most of the previous microfluidic paper-based analytical devices (µPADs). Overall, our developed PT-PAD sensor provides a promising approach for the sensitive detection of Hg2+ levels in both drinking water and Wolffia samples and could be extended to monitor other samples with outstanding detection capability. Moreover, the concept of etching-induced photothermal analysis can be applied to other analytes, making the highly sensitive method suitable for future sensing development.