Electronic Band-Engineered Nanomaterials for Biosafety and Biomedical Application

ConspectusInteraction between nanomaterials (NMs) and biological systems can be beneficial for biological functions but also can present hazards to humans. Nanotoxicology and nanomedicine, as two subdisciplines of nanotechnology, share the same goal of making safer NMs for biomedical application. NMs with unique electronic properties have been widely used for biomedical applications, such as bacterial inactivation, wound healing, tumor therapy, and Alzheimer's disease therapy. Meanwhile, the biosafety of NMs has become a hot topic, and development of effective "safe-by-design" strategies will be beneficial for the wide applications of NMs in the biomedical field. However, it is currently hard to establish a property–activity relationship between NMs and their biosafety and biomedical applications, especially for electronic band structure including conduction band energy (Ec), valence band energy (Ev), Fermi energy (Ef), and bandgap energy (Eg). Eg determines the suitable lights used to excite NMs, and Ec and Ev determine the redox abilities of photoinduced electrons and holes, while Ef dominates the charge transfer process within NMs. Therefore, through modulating the electronic band structure of NMs, not only can the biosafety of NMs be elevated, but also the photoelectronic performance can be improved, providing a profound understanding to the design of functional NMs for the biomedical application with excellent biocompatibility.In this account, we focus on our recent progress in electronic band structure-modulated NMs for biosafety and biomedical application. First, we investigate the toxicities of NMs with different Ec levels and establish safe-by-design strategies to make safer NMs through modulating their electronic properties, such as tuning Ec values of NMs out of the biological redox potential range and tuning the Ef edge far away from the Ev edge. Second, we propose that deep level defect, resonance energy transfer, and narrow band gap intensely correlate with the photothermal performance of NMs and rationally designed heterostructures can significantly improve the photothermal conversion efficacies of these NMs. Third, we introduce a series of NMs with unique heterostructure to promote photoinduced electron–hole spatial separation and improve photodynamic performance for antibacterial and anticancer applications. Among these heterostructures, the thermally retractable heterostructure can create a favorable microenvironment for photodynamic therapy; Z-scheme heterostructure can simultaneously produce oxygen and reactive oxygen species for photodynamic therapy against hypoxic tumor; plasmon–pyroelectric heterostructure can thermally generate reactive oxygen species in an oxygen-independent manner for hypoxic tumor therapy. Furthermore, we describe the photooxidation and antioxidant abilities of NMs for treating Alzheimer's disease through inhibiting amyloid-β self-assembly and scarifying reactive oxygen species. Finally, we propose the challenges and perspectives of electronic band structure-modulated biomedical application of NMs. We expect that this field will attract increasing research interest and create new opportunities for biosafety and biomedical studies of NMs.