Detection and extraction of heavy metal ions using paper-based analytical devices fabricated via atom stamp printing

As a promising concept, microfluidic paper-based analytical devices (μPADs) have seen rapid development in recent years. In this study, a new method of fabricating μPADs by atom stamp printing (ASP) is proposed and studied. The advantages of this new method compared to other methods include its low cost, ease of operation, high production efficiency, and high resolution (the minimum widths of the hydrophilic channels and hydrophobic barriers are 328 and 312 μm, respectively). As a proof of concept, μPADs fabricated with the ASP method were used to detect different concentrations of Cu²⁺ via a colorimetric method. Moreover, combined with a distance-based detection method, these devices achieved a Cu²⁺ detection limit of down to 1 mg/L. In addition, a new paper-based solid-liquid extraction device (PSED) based on a three-dimensional (3D) μPAD with a "3 + 2" structure and a recyclable extraction mode was developed. Specifically, using the characteristics of paper filtration and capillary force, the device completed multiple extraction and filtration steps from traditional solid-liquid extraction processes with high efficiency. The developed PSED platform allows the detection of heavy metal ions much more cheaply and simply and with a faster response time at the point of care, and it has great promise for applications in food safety and environmental pollution in resource-limited areas.