Turn-on fluorimetric sensor for water dispersed volatile organic compounds - A nanosponge approach

Herein we introduce a concept of nanoparticles based, turn-on, fluorimetric approach for sensitive, fast, reversible sensing of low concentrations of volatile organic compounds (VOCs), such as xylene, dispersed in a solution with detection limit as low as 7 ppm achieved without preconcentration. Spontaneous partitioning of VOC to stable, crosslinked polymeric nanoparticles results in nanocapsule formation and change of optical spectra of the dye contained in the nanostructure. For polythiophenes used as dyes, capsule formation results in pronounced increase in diameter and emission increase due to change in form of polymer-dye in the nanostructures: from aggregates of low emission to a dispersed phase of high emission observed at wavelength typical for a dispersed polymer. The selectivity of the native system results from affinity of VOC analyte to polythiophene and nanoparticle material, resulting in xylene selectivity. Increase of the emission signal was observed for xylene concentrations 60 or 120 ppm, depending on the amount of the dye introduced into the nanostructure. Uncommonly for many sensors, in the presence of other solvents lowering of the detection limit was observed and a linear dependence of emission intensity on xylene concentration was obtained. It is shown that using nanosponges pretreated with chloroform a linear dependence of emission in turn on mode is observed within the range from 0 to 200 ppm, with detection limit as low as a few ppm. The proposed novel and original approach is applicable for extending to different nanoparticle materials and dyes combinations, thus sensitivity of the system can be tuned according to needs.