A smartphone readout device for portable and sensitive estimation of Hg via coumarin-modified paper.

The development of cost-effective sensing system for Hg quantitation is highly demanded for environmental monitoring. In this work, we reported an on-site, rapid and portable smartphone-based Hg sensing system integrating coumarin-modified paper as a probe and smartphone readout device as a processing platform. For fluorescent sensing of Hg, the modified paper was fabricated by chemically grafting a coumarin-based probe N-((7-hydroxy-coumarin-3-yl)carbamothioyl)acetamide (HCCA) onto paper, and its physicochemical properties and sensing performance were characterized by elemental analysis, FTIR, XPS, SEM, and fluorescence spectral analysis. The modified paper displayed high selectivity and sensitivity for Hg, accompanied with a distinct fluorescence color change. For portable detection of the fluorescent sensors, a smartphone readout device was designed, consisting of a removable 3D-printed hardware device and an application. Remarkably, the smartphone readout device in cooperation with the modified paper is highly selective and sensitive to Hg with the limit of detection (LOD) of 0.46 ppb, which avoids the requirement of sophisticated equipment and complex operation. The cost-effective sensing system based on smartphone shows a great potential for monitoring of Hg in environmental water.