Field-portable ratiometric fluorescence imaging of dual-color label-free carbon dots for uranyl ions detection with cellphone-based optical platform

Under the public spotlight,uranyl(UO22+)ions has attracted considerable attention for the extreme radioactive and chemical toxicity to ourselves and our environment.Herein,we present a simple and effective ratiometric fluorescence imaging method for the visualizing and quantitative detection UO22+ions by cellphone-based optical platform.The sensing solution was prepared by mixing label-free red carbon dots(r-CDs)and blue carbon dots(b-CDs)together with a fixed photoluminescence intensity ratio of 4:1.When UO22+ions were added,the fluorescence of r-CDs can be selectively quenched,while the fluorescence of b-CDs remains stable without spectral cha nges.With the gradually increase the amounts of UO22+ions,the different response of dual-color CDs resulted in a signification color evolution from deep red to dark purple under the ultraviolet(UV)light illumination.Then,a cellphone-based optical platform was constructed for directly imaging the color change of the samples,and the built-in Colorpicker APP quickly output the red,green and blue(RGB)channel values of these images within one second.Interesting,there was a linear relationship between the ratio of red and blue(R/B)channel values and UO22+ions concentration from 0μmol/L to 30.0μmol/L(R^2=0.92804)with the detection limit of^8.15μmol/L(signal-to-noise ratio of 3).In addition,the optical platform has also been applied to the quantification of UO22+ions in tap water and river water sample.With the advantage of low-cost,portable,easy to operation,we anticipate that this method would greatly improve the accessibility of UO22+ions detection even in resource-limited areas.