Paper-based capacitive sensors for identification and quantification of chemicals at the point of care

The identification and quantification of chemicals play a vital role in evaluation and surveillance of environmental health and safety. However, current techniques usually depend on costly equipment, professional staff, and/or essential infrastructure, limiting their accessibility. In this work, we develop paper-based capacitive sensors (PCSs) that allow simple, rapid identification and quantification of various chemicals from microliter size samples with the aid of a handheld multimeter. PCSs are low-cost parallel-plate capacitors (~$0.01 per sensor) assembled from layers of aluminum foil and filter paper via double-sided tape. The developed PCSs can identify different kinds of fluids (e.g., organic chemicals) and quantify diverse concentrations of substances (e.g., heavy metal ions) based on differences in dielectric properties, including capacitance, frequency spectrum, and dielectric loss tangent. The PCS-based method enables chemical identification and quantification to take place much cheaply, simply, and quickly at the point-of-care (POC), holding great promise for environmental monitoring in resource-limited settings. Not limited to spectrometric techniques: Dielectric properties of chemicals provide alternative fingerprint information to identify and quantify themselves like spectrometric analyses. Low-cost and label-free paper-based capacitive sensors (PCSs) were developed for chemical identification and quantification by using a handheld multimeter in this study (see picture). Considering paper is ubiquitous and environmentally-friendly, the developed PCS provides a promising tool to monitor environmental health and safety at the point of care. [Display omitted] •Low-cost and label-free PCSs as versatile tools for chemical analysis are proposed.•The working principle and affecting factors of the developed PCSs are discussed.•The performances of PCSs can be further improved by optimizing their design.