Induced Circular Dichroism of Methylene Blue in Self-Assembled Pullulan Nanoparticles

This study reports self-assembled pullulan nanoparticles (PUNPs) obtained by the diafiltration method after dissolving phthalic pullulan in dimethylformamide, which was prepared by esterification between the primary hydroxyl groups of the pullulan and carboxylic acids of phthalic anhydride. The morphologies of the PUNPs observed by transmission electron microscopy (TEM) were spherical shapes. The particle sizes of the PUNPs measured by dynamic light scattering (DLS) were around 75.3 nm with −49.32 mV zeta potential. The ordered structure of pullulan measured by circular dichroism (CD) spectroscopy and X-ray diffraction (XRD) was enhanced by the formation of self-assembled polymeric NPs. Methylene blue (MB) used in tissue imaging agent was loaded into PUNPs via ionic bonding of cationic MB and anionic PUNPs, the CD of MB was induced in the PUNPs in the range of 500–700 nm whose crossing point matched κ max in the UV region of MB.