Nanomaterials based on hollow gold nanospheres for cancer therapy

Gold nanoparticles have recently been exploited as versatile nanocarriers in diagnostic and therapeutic drug delivery for cancer nanomedicine, owing to their biocompatibility, low biotoxicity, surface modifiability and plasma optical properties. A variety of gold nanoparticles have emerged for drug delivery, mainly including gold nanorods, gold nanocages, gold nanostars, gold solid nanospheres and hollow gold nanospheres (HGNs). Among these, HGNs have widely been studied for their higher photothermal conversion efficiency, wider spectral absorption range and stronger surface-enhanced Raman scattering compared with solid gold nanospheres. Therefore, nowadays, researchers prefer to use HGNs to other metal nanocarriers, which can not only play the role of controlled-release drugs but also act as photothermal agents for tumor therapy and diagnosis, due to their properties of surface modification. Combined with the Au-S bond on the surface of HGNs, the targeted preparation is loaded to achieve precise drug delivery. With the assistance of the photothermal characteristics of HGNs themselves, the efficacy of loaded drugs in HGNs is enhanced. In addition, HGNs also have vital values in the field of bioimaging, which serve as photothermal imaging agents and Raman scattering-guided preparations due to their surface-enhanced Raman scattering properties to assist researchers in achieving the purpose of tumor diagnosis. In this review, we summarize the synthesis methods of HGNs and the recent application of HGNs-based nanomaterials in the field of cancer diagnosis and therapy. In addition, the issues to be addressed were pointed out for a bright prospect of HGNs-based nanomaterials.