Amine decorated polystyrene nanobeads incorporating π-conjugated OPV chromophore for picric acid sensing in water

Abstract

A solution as well as solid state based sensor has been developed for selective detection of picric acid (PA) in water. Oligo (p-phenylenevinylene) (OPV) incorporated polystyrene nanobeads (PS-OPV-NH₂) having an average size of 180 nm have been synthesized through miniemulsion polymerization. Amine (-NH₂) functionalization was performed on the nanobead surface to enhance the efficiency of the sensor among a library of other nitro-organics and library of cations and anions.

Scheme 1. Schematics for synthesis of amine decorated polystyrene nanobeads via miniemulsion polymerization.

Fig. 1. (A) Emission spectra of PS-OPV-NH₂ and (B) quenching percentage upon addition of different nitro-organic compounds (1 × 10⁻⁴ M) in water. (C) Emission and (D) excitation spectra of PS-OPV-NH₂ collected after addition of varying concentration of PA (1 × 10⁻⁷ to 2 × 10⁻⁴ M). Emission and excitation spectra were collected at λ_ex = 390 nm and λ_em = 445 nm respectively. (E) Plot of changes in fluorescence intensity of PS-OPV-NH₂vs. conc. of PA. (F) Temperature dependent quenching of polymer emission after PA addition. (G) Spectral overlap of excitation/emission spectra of PS-OPV-NH₂ with that of absorption spectra of PA.

Fig. 2. (A) Schematics for the mechanism of quenching of OPV emission by PA in water. (B) Emission spectra of PS-OPV-NH₂. (C) Its comparative quenching percentage upon addition of different cations vs. PA (1 × 10⁻⁴ M) in water. (D) Emission spectra of PS-OPV-NH₂ and (E) its comparative quenching percentage upon addition of different anions vs. PA (1 × 10⁻⁴ M) in water.