Chaotropic anion induced self-assembly of naphthalimide–glutathione nanohybrids: selective recognition of bisulphate anions in aqueous medium

Anion-induced self-assembly is one of the growing research fields as it provides a better understanding of natural self-assemblies such as DNA, proteins, peptides, etc. Peptides are well known for their aggregation properties owing to their hydrogen bonding interactions. Herein, nanohybrids of the glutathione tripeptide and naphthalimide based compounds were fabricated, in order to explore their self-assembly behaviour. The naphthalimide based compounds were processed into organic nanoparticles using a re-precipitation method and then into nanohybrids with a tripeptide under ultrasonication conditions to get nanohybrids NH-1, NH-2 and NH-3. The morphology of prepared nanohybrids was studied by HRTEM analysis. The photophysical studies of these nanohybrids were carried out by adding various anions. NH-1 shows enhanced fluorescence intensity with bisulphate anions and the rest of the anions do not induce any change in the fluorescence intensity. Furthermore, the morphology of these nanohybrids was monitored using HRTEM and STEM. With bisulphate anions, a beautiful butterfly shaped self-assembly was observed for NH-1. The increase in intensity was a result of the aggregation induced enhanced emission mechanism. These self-assemblies have potential applications in the recognition of bisulphate with a limit of detection (LOD) of 3 nM and a limit of quantification of 10 nM respectively.