A silica nanoparticle supported fluorescence “turn-on” fluoride ion sensing system with tunable structure and sensitivity

Abstract

Amino-silane modified silica nanoparticles (SNP-APTMS and SNP-TMSPEDA) doped with silyl-ether protected fluorescein isothiocyanate (FITC-OSMDBT) were synthesized via a sol–gel method in a simple three-step reaction to give fluoride ion probes SNP-TMSPEDA-FITC-OSMDBT (sensor A) and SNP-APTMS-FITC-OSMDBT (sensor B). The sensors were characterized using FT-IR, EDX, TGA, and fluorescence spectroscopy. It was observed that, at fluoride ion and FITC-OSMDBT mole equivalent titration ratio of x : x, the emission spectra of both sensors were similar when x = 1.0; however, at x = 3.0, 6.0, and 9.0, sensor B displayed 3 fold the emission intensity of sensor A. This phenomenon was attributed to non-radiative emission energy transfer mechanisms, which were controlled by the FITC-OSMDBT loading. The steric hindrance difference present on N-[3-(trimethoxysilyl) propyl] ethylenediamine (TMSPEDA) and (3-aminopropyl)trimethoxysilane (APTMS) ensured that different amounts of FITC-OSMDBT were loaded on each sensor. At x = 3.0, 6.0, and 9.0, the emission intensity increased linearly with [F⁻] in DMSO; thus, from the working curve of sensor A, the fluoride ion detection range of sensor B could be calculated and vice versa. The structure of the sensing system being proposed is simple, sensitive to F⁻, and may prove useful with respect to the development of fluoride anion sensors with structures which can be easily modified to produce sensors with varying detection ranges.