Self-assembled nanofibers of perylene diimide for the detection of hypochlorite in water, bio-fluids and solid-state: exogenous and endogenous bioimaging of hypochlorite in cells.

A fluorescent probe PDI-DAMN based on perylenediimide containing diaminomaleonitrile at the bay-position was designed and synthesized for the detection of ClO-. PDI-DAMN self-assembled as nanofibers with diameters in the range of 100-200 nm in H2O : CH3CN (1 : 1). The addition of ClO- into PDI-DAMN resulted in the disintegration of nanofibers 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 a hypochromic effect on the ICT band at 528 nm and 'turn-on' fluorescence enhancement at 508/554 nm due to the oxidative cleavage of -C[double bond, length as m-dash]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 ClO- with the detection limits of 1 and 10 nM, respectively. Optical studies performed on spiked urine and blood serum samples showed good estimation and recovery of ClO- (100 ± 5%). TLC-based test-strips coated with PDI-DAMN changed colour upon the addition of ClO- with detection as low as 7.44 ng cm-2. The application of PDI-DAMN for the bio-imaging of both exogenous and endogenous ClO- in MG-63 cells with good biocompatibility has also been demonstrated. The detailed mechanism of the interactions of ClO- with PDI-DAMN using 1H NMR titration, DFT studies and response mechanism of pH are also discussed.