Paper-based microfluidic analytical devices for colorimetric detection of toxic ions: A review

Paper-based microfluidic analytical devices (μPADs) are becoming valuable tools in analytical area due to their attractive passive movements of analyte without any external forces due to capillary phenomenon. Techniques used to design microfluidic patterns are cost-effective, less sample requirement, environmentally benign and rapid analysis. The application of μPADs with intricate fabrication methods have emerged over a decade in several fields such as diagnostics, biological, food safety, environemental analysis, electrochemical and colorimetric detections. The present review addresses colorimetric detection of metal ions and nitrites from various sources using a simple filter paper (Whatman®) as μPADs, since filter paper is white in color, possibility of liquid transport through capillary action and high surface area offers high detection efficiency. Due to its importance as an analytical tool, an attempt has been made here to critically discuss the present scenario and future prospects of this technique.