One step synthesis of crosslinked fluorescent microspheres for the effective and selective sensing of explosives in aqueous media

Herein, new pyrene-based polymeric microbeads were simply synthesized in one-step as fluorescence chemosensor for high precision detection of nitroaromatic compounds (NACs) such as 2,4,6-trinitro toluene (TNT), 2,4-dinitro toluene (DNT) and 2,4,6-trinitrophenol (picric acid, PA). Firstly, nonhydrolyzable 4-(1-pyrenyl)-styrene (PySt) monomer, in which the pyrene units are directly attached to styrene group, was synthesized by Suzuki Coupling reaction and polymerized in the presence of ethylene glycol dimethacrylate (EGDMA) as crosslinker by distillation precipitation polymerization. Highly crosslinked almost monodisperse poly(4-(1-pyrenyl)-styrene-co-ethyleneglycoldimethacrylate), P(PySt-EGDMA) microspheres with 850–1000 nm particle size distribution were successfully obtained by an effortless and very quick -one hour- polymerization reaction. One of the most important advantages of the microbeads with this particle size range was that they give homogeneous and stable dispersions in both aqueous and organic media, which facilitates detection studies. Detection studies and quenching activities of these microbeads against NACs were investigated under different solvent conditions such as water, acetonitrile, methanol and tetrahydrofuran. During the fluorescence measurements, each dispersion of P(PySt-EGDMA) microbeads showed very strong fluorescence activity in their bare form, even at very low concentrations (6.67 µg/ml solvent). Moreover, among all suspension, the responses in aqueous media against NACs demonstrated the best fluorescence quenching activities. When the responses of the aqueous dispersion to NACs are compared over the Ksv values, the highest quenching ability of the microbeads was found against DNT (Ksv: 1.4 × 10⁶ M⁻¹). At the same time, DNT could be detected at the nanomolar level with the lowest calculated limit of detection (LOD) value, 1.39 ppb. All these facts demonstrate that the aqueous dispersion of P(PySt-EGDMA) microbeads is highly selective and sensitive to DNT.