A novel technique to overcome fluid flow influence in carbon quantum dots/paper-based analytical devices

Paper-based analytical devices are promising choices for rapid tests and lab-on-chip detection techniques. Carbon quantum dots (CQDs), on the other hand, are biocompatible nanomaterials, which are industrially promising, due to their fast and cost-effective gram-scale synthesis techniques, as well as their significantly high and stable photoluminescence (PL) properties, which are durable and reliable over a year. However, there have been limitations in the entrapment of CQDs on cellulose papers in a way that their PL is not influenced by the flowing of the CQDs with the stream of analyte fluid, making the sensors less accurate at very low concentrations of liquid analytes. Therefore, in this investigation, a polyvinyl alcohol/alkaline-based method was systematically generated and developed to entrap CQDs inside a 3D crystalline matrix on paper, in a way that they can be used directly as probes for a simple drop-and-detect method. As a proof of concept, N/P-doped CQD on cellulose paper was used to make fluorescent paper-based analytical devices for identifying traces of Hg²⁺ of around 100 ppb. The designed sensor was tested over several months, to study its durability and functionality over long periods, for potential industrial applications.