Preparation and characterization of sulfonated chitosan-modified gold nanoparticles and their surface electronic payload of charged drugs.

Chitosan (CS), a kind of naturally produced polysaccharide with extraordinary biocompatibility and biodegradation, shows much potential to act as reducing and stabilizing agent in the synthesis of gold nanoparticles (AuNPs) for drug delivery. To solve the poor solubility and expand the pharmaceutical applications of CS, various CS derivatives through rational design have been developed and further used to prepare, stabilize, and mediate self-assembling of gold materials. Herein, we chose sulfonic chitosan as a stabilizing reagent for the synthesis of highly stable AuNPs (AuNP/SCSs) with diameters of about 3 nm. For investigating their surface electronic payload of charged drugs, the negatively charged fluorescence isothiocyanate (FITC) and positively charged Rhodamine B (Rb) were used as models to be modified on the surface of the AuNP/SCSs via a layer-by-layer (LbL) method. With a basis of the fluorescence resonance energy transfer (FRET) principle, via adjusting the distance between AuNPs and fluorescent molecules by tuning the layers of charged polymers, the regulation of the fluorescence intensity of the fluorescent molecules has been achieved. In addition, the drug loading efficiency was investigated.