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

Abstract

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 –CN– 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.