Naphthalimide-Based AIEgens for Sensing Protein Disulfide Isomerase through Thiol-Disulfide Redox Exchange

Aggregation-induced emission (AIE)-based fluores-cent organic nanoparticles (FONPs) with distinctive characteristics are emerging as superior sensors due to their facile fabrication, high signal-to-noise ratio, and good biocompatibility. The present article delineates the detection and analysis of the redox behavior of the protein disulfide isomerase (PDI) enzyme by exploitation of the AIE of novel naphthalimide (NI) derivatives having thiol (-SH) and disulfide (-S-S-) moieties. Self-aggregated spherical-shaped organic nanoparticles were prepared by synthesized NI-based amphiphiles (NISH, NISS, NINSS, and TNINSH) through J-type aggregation in DMSO-water (f(w) = 99 vol %). Naphthyl residue containing NI-derived amphiphiles (NINSS and TNINSH) exhibited AIE (blue and yellow) at 470 and 550 nm, respectively, in DMSO-water (f(w) = 99 vol %). NINSS and TNINSH FONPs were suitably utilized in sensing PDI through their redox nature of thiol-disulfide exchange. Fluorescence quenching of NINSS FONPs was observed due to reduction of disulfide to thiol by PDI, whereas emission intensity was progressively red-shifted and enhanced (Dual-AIE) for TNINSH (containing ER-targeting N-tosylethylenediamine), owing to oxidation of thiol to disulfide by PDI. NINSS and TNINSH FONPs were found to be highly efficient in sensing PDI through the AIE-based fluorescence off/on mechanism having limits of detection of -12.6-17.7 and -11.7-16.5 ng/mL, respectively. In vitro cell imaging for NIH3T3 (noncancer) and B16F10 (melanoma) cells with NINSS and TNINSH FONPs displayed excellent diagnosis of eukaryotic cells upon interaction with indigenous PDI. Notably, detection of cancer cells was more sensitive over the noncancerous cells by these FONPs due to overexpression of PDI within cancer cells.

Automated summary

Aggregation-induced emission (AIE) based fluorescent organic nanoparticles (FONPs) are superior sensors with easy fabrication, high signal-to-noise ratio, and good biocompatibility. This article focuses on the detection and analysis of the redox behavior of the protein disulfide isomerase (PDI) enzyme using novel naphthalimide (NI) derivatives with thiol and disulfide moieties. The synthesized NI-based amphiphiles (NISH, NISS, NINSS, and TNINSH) formed self-aggregated spherical-shaped organic nanoparticles, exhibiting AIE in DMSO-water. The NINSS and TNINSH FONPs were successfully utilized for sensing PDI through their thiol-disulfide exchange and showed high efficiency with limits of detection of -12.6-17.7 and -11.7-16.5 ng/mL, respectively. In vitro cell imaging with NINSS and TNINSH FONPs displayed excellent diagnosis of eukaryotic cells, particularly cancer cells, due to the overexpression of PDI.