Chitosan-Coated Gold Nanorods as Contrast Agents for Hyperspectral Photoacoustic Imaging of Murine Bladder Cancer

In the present work, gold nanorods (GNRs) are synthetized from metal salt precursors in presence of CTAB (cetyl trimethylammonium chloride) in aqueous environment, leading to the formation of nanoparticles capped by a double bilayer of surfactant. Then, high-molecular-weight chitosan is chemically modified with thioglycolic acid to insert thiol groups on the sugar backbone. Thiol moieties have been exploited due to their ability of binding gold, replacing cytotoxic CTAB from the surface of the nanoparticle. Chitosan is able to strongly interact with bladder wall cells and GNRs display a strong optical absorption in the NIR: therefore, the nanosystem is tested as contrast agent for multispectral photoacoustic imaging of the bladder. Firstly, biodistribution and toxicity of the nanosystem is tested in vivo on mice which have been intravesically perfused with chitosan-coated GNRs. Then, catheterally perfused murine bladders are studied ex vivo by dual-modality ultrasound/photoacoustic imaging, highlighting the localization of GNRs in part of the urothelium. Finally, acquired multispectral data are decomposed by a multivariate curve resolution algorithm (MCR-ALS) which allows the successful separation of the spectral contributions of different photoabsorbers in different distribution images, generating a refined spectrum related to each pure component.