Photoluminescence from Chitosan for Bio-Imaging

Photoluminescent behaviours of chitosan were investigated. Photoluminescence can be observed from aqueous solution of chitosan, and CO2 treatment can improve the intensity of photoluminescence. The maximum emission is obtained with an excitation at ~336 nm, and the emission wavelength is dependent on the excitation wavelength with a longer excitation wavelength leading to a longer emission wavelength. The chemistry of chitosan before and after CO2 treatment was characterised; and the results reflect that carbamato anion is formed via the reaction between the amines and CO2, and is the fluorophore of the photoluminescence observed. Furthermore, chitosan was applied as an imaging agent for imaging MCF-7 cells using confocal microscopy. Blue and bright green imaging of the cells can be obtained via tuning the excitation and emission wavelength. Together with a low cytotoxicity reflected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide evaluation, fluorescent chitosan is promising for bio-imaging.