Oligochitosan-stabilized photoluminescent gold nanoconstructs for optical bioimaging

Donghyuck Yoo, Dongwon Lee

Gold nanoclusters (AuNCs) are typically composed of several to tens of gold atoms which are stabilized with biomacromolecules such as bovine serum albumin (BSA). Au NCs fluoresces in the visible to near infrared region, in a size-dependent manner. AuNCs solutions have potential as fluorophore in a wide range of biomedical applications such as biodetection, biosensing and bioimaging in vitro and in vivo. However, their stability and harsh condition of preparation limit their biomedical application. BSA stabilized AuNCs (BSA-AuNCs) were prepared by mixing HAuCl4 solution with BSA solution for 24 h at 37°C under basic condition. BSA-AuNCs were then mixed with oliogochitosan (OCS) to generate BSA-Au-OCS nanocomplexes. The physicochemical and optical properties of BSA-Au-OCS nanocomplexes were studied using a fluorospectrometer. Their potential as a bioimaging agent in vivo and in vitro was evaluated using a fluorescent imaging instrument. BSA-stabilized AuNCs solutions were mixed with oligochitosan (OCS) to develop BSA-Au-OCS nanocomplexes of a mean diameter of ~250 nm. BSA-Au-OCS nanocomplexes could emit light at 620 nm and the complexation with OCS did not affect the photophysical properties of BSA-AuNCs. BSA-Au-OCS nanocomplexes showed less cytotoxicity than BSA-AuNCs and was readily taken up by cells. BSA-Au-OCS nanocomplexes showed strong fluorescence in tissues. We developed stable BSA-Au-OCS nanocomplexes which fluoresce in the near infrared region. BSA-Au-OCS nanocomplexes exhibited significantly less cytotoxicity and strong fluorescence emission, suggesting potential for biomedical applications.