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

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 x 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 x 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.