A dual “Turn-on/Turn-off” “FRET” sensor for highly sensitive and selective detection of lead and methylene blue based on fluorescent dansyl tagged copolymer and small molecule diketopyrrolopyrrole.

Abstract

Here we report, a multimodal sensing platform for sensitive and selective detection of heavy metal Lead (Pb +2) and organic dye (Methylene Blue) employing a novel FRET pair between a fluorescent polymer and a small molecule. The FRET pair consists of the highly fluorescent dansyl tagged copolymer P(MMA-co-Dansyl-Ala-HEMA) (DCP) and small molecule diketopyrrolopyrrole (DPP). The overlap integral of the FRET pair is calculated to be 1.14 × 10 16 nm 4 /(M*cm) and energy transfer efficiency is determined to be 25%. The fluorescence intensity of the studied FRET pair has been found to be quenched ("Turn Off") and enhanced ("Turn On") in the presence of methylene blue (MB) and lead (Pb +2) respectively. The FRET pair shows a strong affinity for Pb +2 ions with very low detection limit (LOD) (27.8 ppm). High K SV (3.9 × 10 4 M −1) for MB sensing with LOD value 295 ppb indicates enhanced photo-induced electron transfer from FRET pair to MB. The metal-induced modulation of the self-assembled polymer-small molecule-Pb complex in the solution lead to the photoluminescence enhancement in the presence of Pb +2 and the dynamic quenching is established as the fluorescence Turn-off mechanism in the presence of MB dye. Our multimodal FRET sensing probe offer a common platform for the selective detection of a broad range of toxic pollutants which opens up its possibility of use in field applications.