Green Synthesis of Superior Molecular Fluorophores from Chitosan Assisted with Cellulase for Cell Nucleus Imaging and Photosensitive Printing

Abstract

In this study, a facile and green route was designed using hydrolyzed chitosan as precursor to fabricate superior molecular state fluorophores based on the Maillard reaction (MR). The fluorophores exhibit excitation-dependent photoluminescence behavior, emitting multicolor fluorescence. The CCK-8 assay shows the low cytotoxicity of the Maillard reaction products (MRPs). The properties of the MRPs were associated with the molecular size. The high-molecular-weight fraction (>10 kDa) contains a large quantity of brown products which cause fluorescence quenching by an inner-filter effect. The medium-molecular-weight fraction (5–10 kDa) is able to permeate into the living cells and specifically stains the nucleus for stable imaging. The low-molecular-weight fraction (<3 kDa) possesses a dramatically high quantum yield of 30.4% and excellent ion stability, as well as a pH-responsive property; it can serve as a potential pH sensor and fluorescent ink for photosensitive printing. The potential applications of MRPs fractions in different fields are proposed, significantly improving the utilization efficiency. Additionally, this work provides a new perspective on designing and preparing large-scale metal-free fluorescence materials with high safety and good water solubility in a green and mild manner.