Imaging-based fluorescent sensing platform for quantitative monitoring and visualizing of fluoride ions with dual-emission quantum dots hybrid.

Herein, a ratiometric fluorescence sensing strategy coupled with smartphone imaging-based sensing platform was proposed for the on-site determination of fluoride ion (F) with high sensitivity and accuracy. The principle of sensing strategy is based on the fluoride-promoted Si-O bond cleavage of 2-(tert-butyldiphenylsilyloxy)phenol (2-TBDPSP) to release 2-hydroxyphenolate, which rapidly auto-oxidized to ortho-quinone. As excellent electron acceptor, these quinone species covalently bonded on the surface of dual-emission amino-modified quantum dots (QDs) nanohybrid via a Michael's type adduction, quenching the fluorescence of green-emitting QDs on the surface of the nanohybrid, while not affecting the fluorescence of red-emitting QDs embedding silica nanospheres. Upon exposure to different amounts of F, the variations of dual emission intensity ratios display continuous color changes from green to red, which could be directly observed by naked eyes. Then a smartphone imaging-based sensing platform was constructed by 3D-printing technology. The smartphone camera acquired the images of fluorescence derived from samples, and the Color Picker APP installed in smartphone continued to read out the Red, Green and Blue (RGB) channel values of these images. There was a linear relationship between the ratio of Red and Green (R/G) and F concentration in the range of 0-70.0 μM. The limit of detection (LOD) was estimated to be 2.0 μΜ, much lower than the allowable level of F (~63.16 μM) in drinking water set by World Health Organization. This methodology reported here is low-cost, portable, easy-operation, and thus potentially attractive for F determination without the need of elaborate equipment.