Lipase sensing by naphthalene diimide based fluorescent organic nanoparticles: a solvent induced manifestation of self-assembly.

The precise control of supramolecular self-assembly is gaining utmost interest for the demanding applications of manifested nano-architecture across the scientific domain. This study delineates the morphological transformation of naphthalene diimide (NDI) derived amphiphiles with varying water content in dimethyl sulfoxide (DMSO) and the selective sensing of lipase using its aggregation-induced emission (AIE) properties. To this end, NDI-based, benzyl alcohol protected alkyl chain (C1, C5, and C10) linked amphiphilic molecules (NDI-1,2,3) were synthesized. Among the synthesized amphiphiles, benzyl ester linked C5 tailored naphthalene diimide (NDI-2) exhibited AIE with an emission maximum at 490 nm in a DMSO-water binary solvent system from fw = 30% and above water content. The fibrous morphology of NDI-2 at fw = 30% got gradually transformed to spherical aggregated particles along with steady increment in the emission intensity upon increasing the amount of water in DMSO. At fw = 99% water in DMSO, complete transformation to fluorescent organic nanoparticles (FONPs) was observed. Microscopic and spectroscopic techniques demonstrated the solvent driven morphological transformation and the AIE property of NDI-2. Moreover, this AIE of NDI-2 FONPs was employed in the selective turn-off sensing of lipase against many other enzymes including esterase, through hydrolysis of a benzyl ester linkage with a limit of detection 10.0 ± 0.8 μg L-1. The NDI-2 FONP also exhibited its lipase sensing efficiency in vitro using a human serum sample.