Thin-film probes have been developed for the reversible detection and separation of picric acid (PA) with extreme sensitivity in aqueous media. The free radical copolymerization of dimethylacrylamide (DMA), benzophenone acrylamide (BPAM), and glycidyl methacrylate (GMA) with a feed ratio of 95:1:4 yielded [p(DMA- co-BPAM- co-GMA)] (P1). P1 was transformed to the final polymeric probe, P2, by a subsequent ring-opening reaction between N-(pyren-1-yl-methyl)propan-1-amine (Py-PA) with the epoxide unit of P1. P2 exhibited rapid and selective sensing properties toward PA in aqueous media via turn-off fluorescence emission. The detection sensitivity was tuned precisely by varying the pH of the solution. After the immobilization of P2 on a quartz slide by spin-coating, followed by exposure to UV light, the resulting film exhibited an attogram-level detection limit toward PA. The photoinduced electron transfer together with an energy-transfer process between PA and the pyrene units of P2 were maximized by the strong π-π stacking of pyrene units of P2, which, in turn, induced rapid exciton energy diffusion. Furthermore, the separation of PA from the mixture of the various nitroaromatic compounds by the P2 film was achieved. Whereas the detection process of PA was reversible and repeatable over multiple cycles, the P2 film could be recycled.
Keywords: detection; fluorometric; pH-responsive; picric acid; pyrene; thin film.