Carbon nanodots as fluorescent platforms for recognition of fluoride ion via the inner filter effect of simple arylboronic acids. Experimental and theoretical investigations

Abstract

In this work, a new type of water soluble fluorescent assay was designed for fluoride ion based on the inner filter effect (IFE) of simple para-substituted arylboronic acids. Carbon nanodots (CDs) as the green and nontoxic carnbonic nanomaterials were used as the fluorophores and arylboronic acids as the absorbers. The reaction of fluoride ion with boron center of arylboronic acids tuned the absorption profiles toward longer or shorter wavelengths. In case of an increase in the spectral overlap between absorber and fluorophore, a decrease in fluorescence intensity of CDs was observed and considered as a response for quantitative fluoride measurement. The minimum detectable value of fluoride by these assays fulfilled the Environmental Protection Agency (EPA) requirement for water safety. The simple design of this assay together with avoidance of any covalent linkage between fluorophore and absorbers offers a cost effective, selective and sensitive fluoride sensor in aqueous environments. Furthermore, we have carried out density functional theory calculations to study the electronic structures and optical absorption spectra of the arylboronic acids before and after reaction with fluoride. Excellent agreement between the experimental result and theoretical calculations enables for prediction of spectral change of aryl boronic acids upon reaction with fluoride. In particular, the effect of fluoridation reaction on the excitation spectrum of CDs through IFE could be simply predicted by the theoretical calculation. Therefore, by using the present system, design of even more successful probes would be feasible for fluoride recognition in aqueous media.