Recent progress of smartphone-assisted paper-based analytical devices (PADs) for multiplex sensing: Focusing on colorimetric and optical sensors for environmental monitoring, food safety, and biomedical application

The request for rapid and efficient sensing methods has been increased in different fields. Affordability, portability, accuracy, and multiplex sensing, are important factors in the development of high-performance analytical methods. Paper based analytical devices (PADs) based on smartphone for detection of multiplex targets have attracted attention as high throughput sensing platforms. These robust sensing devices have been fabricated based on using different papers as sensing zones and smartphones as transductor and analyzer of signals. The integration of smartphone with paper-based sensors have presented high sensitivity as well as low cost and ease of use sensing approaches. This adaptation is more prominent in sensing and biosensing due to the ability of smartphone to analyze signals and connect to the Internet. The modification of papers with biological receptors and materials has provided multiplex detection based on hydrophobic and hydrophilic areas, bioreceptors/receptors, and using different papers. In this review, the fundamentals and mechanism of multiplex detection of PADs have been discussed. In addition, the importance of smartphones and their compatibility with portable and accessible devices in multiplex sensing of biomedical analysis, food safety, and environmental monitoring has been considered. In order to complete discussion, the advantages, limitations, and gap in this have been summarized.