Multilayer Paper-Based Device for Colorimetric and Electrochemical Quantification of Metals

TLDR

Metal release into the environment is a growing concern due to widespread health effects, yet routine quantification is cost‑prohibitive, often exceeding $100 per sample. The study presents a low‑cost, three‑dimensional microfluidic paper‑based device that integrates colorimetric and electrochemical detection to make toxic metal analysis accessible worldwide. The device employs a three‑layer architecture with distinct colorimetric and electrochemical layers, enabling separate chemistries on a single sample and allowing analysis of particulate metals collected on air‑sampling filters. It achieved detection limits of 0.12 µg Cr on the colorimetric layer and 0.25 ng Cd/Pb on the electrochemical layer, demonstrated selectivity against common interferences, and accurately quantified particulate metals on air‑sampling filters, matching certified reference values.

Abstract

The release of metals and metal-containing compounds into the environment is a growing concern in developed and developing countries, as human exposure to metals is associated with adverse health effects in virtually every organ system. Unfortunately, quantifying metals in the environment is expensive; analysis costs using certified laboratories typically exceed $100/sample, making the routine analysis of toxic metals cost-prohibitive for applications such as occupational exposure or environmental protection. Here, we report on a simple, inexpensive technology with the potential to render toxic metals detection accessible for both the developing and developed world that combines colorimetric and electrochemical microfluidic paper-based analytical devices (mPAD) in a three-dimensional configuration. Unlike previous mPADs designed for measuring metals, the device reported here separates colorimetric detection on one layer from electrochemical detection on a different layer. Separate detection layers allows different chemistries to be applied to a single sample on the same device. To demonstrate the effectiveness of this approach, colorimetric detection is shown for Ni, Fe, Cu, and Cr and electrochemical detection for Pb and Cd. Detection limits as low as 0.12 μg (Cr) were achieved on the colorimetric layer while detection limits as low as 0.25 ng (Cd and Pb) were achieved on the electrochemical layer. Selectivity for the target analytes was demonstrated for common interferences. As an example of the device utility, particulate metals collected on air sampling filters were analyzed. Levels measured with the mPAD matched known values for the certified reference samples of collected particulate matter.