Frontier exploration for gold-based nanostructures for photothermal bacterial lysis

Pathogenic microorganisms can lead to serious infection. The increased multi-drug-resistant bacteria poses a great threat to the survival of humans and animals due to gene mutations and various mechanisms of drug resistance, which attracts people's attention to alternative solutions against bacteria. Developing new antibacterial nanomaterials is an effective way to solve this problem. Due to the excellent biocompatibility, photothermal stability, photothermal conversion efficiency, and easy modification of gold nanostructures, the research has focused on the design of gold nanostructures with activated antibacterial properties induced by light irradiation for use against drug-resistant bacteria. At present, a variety of gold nanostructures were used for photothermal bacterial lysis, and their antibacterial properties can be enhanced by adding components for specific targeting or modulating the structure and size for enhanced efficiency of photothermal conversion. The photoactive gold based nanostructure displayed the great advantages of killing pathogenic bacteria especially for the drug-resistance bacteria, due to the physical damage to the bacteria from the gold based nanostructure, which is totally different from the mechanism of disinfection of traditional antibiotics. They have a great and wide application for solving the problem faced now. In this review, we introduced the photoactive gold nanostructures used to fight for pathogen diseases, especially for drug-resistant bacteria infection. The basic principles, important developments, promising applications and limitations of the current technology are revealed. Initially, the diversity of gold nanostructures was introduced (gold nanoparticles, gold nanostars, gold nanorods, gold nanocages, gold nanoshells, etc.), due to their amazing local surface plasmon resonance (LSPR) and oxidation resistance, which can present one advantage of antimicrobial activity by the hyperthermia to lysis the bacteria in a short time. Near-infrared irradiation (NIR) was widely used in these photoactive gold nanomaterials, with the ability to penetrate the skin tissue from 5 to 10 mm and low damage to tissue. It is another advantage compared to other antimicrobial materials. Subsequently, the surface modification of gold nanostructure was addressed in this review due to the significance of modulating the property of gold nanostructure to enhance the antimicrobial activity and the specificity to pathogens, as well as lowering the side effect of damaging the normal cell. For instance, one strategy is proposed to modify the antibody or specific peptide against bacteria on the surface of gold nanostructure to regulate both the LSPR of gold nanostructure and specificity of bacteria. Another one is the combination strategy which includes the doping of Ag and Pt on the surface of the gold nanostructure, 2D nanomaterial (graphene oxide nanosheet or black phosphorus nanosheet)/gold nanostructure, and gold nanostructure with antibiotics or antimicrobial peptides, etc. All the approaches summarized in this review could facilitate enhancing the efficiency of killing bacteria by the photoactive gold based nanostructures. Finally, the challenges and perspectives in this area were proposed. For instance, the construction of smart material based on gold nanostructure was emergent in further exploration, according to the microenvironment of infection sites. The biosafety of photoactive gold based nanomaterial is still the big issue in the next step, which is the key factor for further clinical application. In general, the gold based nanomaterial with a variety of nanostructures displays the designable structure in a controlled manner, the excellent photoactive properties, and amazing hyperthermia feature, which sheds light on further clinical applications, such as biosensor and biomedicine.