Functionalized chitosan with self-assembly induced and subcellular localization-dependent fluorescence ‘switch on’ property

Abstract

Chitosan-based polymers are commonly used as drug delivery carriers and for functional modification of nanoparticle/polymers. Herein, we report a functional chitosan oligosaccharide with a self-assembly-induced fluorescence ‘switch on’ property, and that also exhibits a similar type fluorescence ‘off’ to ‘on’ state via subcellular localization. Specifically, chitosan oligosaccharide was conjugated with aggregation induced emission (AIE) active tetraphenylethene (TPE) and lipophilic–cationic triphenylphosphonium (TPP) molecules. The resultant functional chitosan self-assembles into 50–200 nm particles, whereby TPE offers a self-assembly induced fluorescence ‘switch on’ property and TPP offers cell uptake via lipophilic–cationic surface properties. The self-assembled chitosan nanoparticle enters into the cell predominately by lipid-raft endocytosis and exhibit a fluorescence ‘off’ to ‘on’ state upon localization at the lysozome. We have shown that adjustment of the number of TPP/TPE molecules bound to each chitosan is critical for the self-assembly induced fluorescence ‘switch on’ property and the subcellular localization-dependent fluorescence ‘off’ to ‘on’ state performance. Other fluorescence ‘switch on’ type sub-cellular imaging probe could be designed with appropriate functional modification of chitosan oligosaccharide or similar macromolecules.