Self-assembled nanofibers of perylene diimide for detection of hypochlorite in water, bio-fluids and solid state: Exogenous and endogenous bioimaging of hypochlorite in cells
Fluorescent probe PDI-DAMN based on perylenediimide containing diaminomaleonitrile at bay- position has been designed and synthesized for detection of ClO-. PDI-DAMN self-assembled as nano-fibers with diameters in the range of 100–200 nm in H2O:CH3CN (1:1). The addition of ClO- into PDI-DAMN resulted in disintegration of nano-fibers into flake-like aggregates of smaller size (50-80 nm) as supported by SEM and DLS data. The addition of ClO- to HEPES buffer-CH3CN solution (1:1,v/v, pH 7.4) of PDI-DAMN caused hypochromic effect on ICT band at 528 nm and ‘turn-on’ fluorescence enhancement at 508/554 nm due to oxidative cleavage of –C=N- bond. A linear correlation plot between the concentration of ClO- versus fluorescence intensity (R2 = 0.9968)/ absorbance (R2 = 0.9988) in the concentration range 0–7 nM (fluorescence) / 0–90 nM (absorbance) could determine the ClO- with detection limit of 1 and 10 nM, respectively. Optical studies performed on spiked urine and blood serum samples showed good estimation and recovery of ClO- (94±3%). TLC based test-strips coated with PDI-DAMN changed color upon addition of ClO- with detection as low as 3.72 ng/cm2. The application of PDI-DAMN for bio-imaging of both exogenous and endogenous ClO- in MG-63 cells with good biocompatibility has also been demonstrated. The detailed mechanism of interaction of ClO- with PDI-DAMN using 1H NMR titration, DFT studies and response mechanism of pH are also discussed.