Around the globe, surges of bacterial diseases are causing serious health threats and related concerns. Recently, the metal ion release and photodynamic and photothermal effects of nanomaterials were demonstrated to have substantial efficiency in eliminating resistance and surges of bacteria. Nanomaterials with characteristics such as surface plasmonic resonance, photocatalysis, structural complexities, and optical features have been utilized to control metal ion release, generate reactive oxygen species, and produce heat for antibacterial applications. The superior characteristics of nanomaterials present an opportunity to explore and enhance their antibacterial activities leading to clinical applications. In this review, we comprehensively list three different antibacterial mechanisms of metal ion release, photodynamic therapy, and photothermal therapy based on nanomaterials. These three different antibacterial mechanisms are divided into their respective subgroups in accordance with recent achievements, showcasing prospective challenges and opportunities in clinical, environmental, and related fields.

An upsurge in the multidrug-resistant (MDR) bacterial pestilence is a global cause for concern in terms of human health. Lately, nanomaterials with photothermal effects have assisted in the efficient killing of MDR bacteria, attributable to their uncommon plasmonic, photocatalytic, and structural properties. Examinations of substantial amounts of photothermally enabled nanomaterials have shown bactericidal effects in an optimized time under near-infrared (NIR) light irradiation. In this review, we have compiled recent advances in photothermally enabled nanomaterials for antibacterial activities and their mechanisms. Photothermally enabled nanomaterials are classified into three groups, including metal-, carbon-, and polymer-based nanomaterials. Based on substantial accomplishments with photothermally enabled nanomaterials, we have inferred current trends and their prospective clinical applications.

The metallic phase of 1T-MoS2 nanoflowers (NFs) and the semiconducting phase of 2H-MoS2 NFs were prepared by a facile solvothermal and combustion method. The antibacterial activities, reactive oxygen species (ROS) generation, and light-driven antibacterial mechanism of metallic 1T-MoS2 NFs and semiconducting 2H-MoS2 NFs were demonstrated with the bacterium Escherichia coli (E. coli) under light irradiation. Results of the bacterial growth curve and ROS generation analyses revealed higher light-driven antibacterial activity of metallic 1T-MoS2 NFs compared to semiconducting 2H-MoS2 NFs. Electron paramagnetic resonance (EPR) spectroscopy demonstrated that the ROS of the superoxide anion radical •O2 – was generated due to the incubation of 1T-MoS2 NFs and E. coli with light irradiation. Furthermore, E. coli incubated with metallic 1T-MoS2 NFs exhibited significant damage to the bacterial cell walls, complete bacterial destruction, and abnormal elongation after light irradiation. The light-driven antibacterial mechanism of metallic 1T-MoS2 NFs was examined, and we found that, under light irradiation, photoinduced electrons were generated by metallic 1T-MoS2 NFs, and then the photoinduced electrons reacted with oxygen to generate superoxide anion radical which induced bacterial death. For semiconducting 2H-MoS2 NFs, photoinduced electrons and holes rapidly recombined resulting in a decrease in ROS generation which diminished the light-driven antibacterial activity.

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An outbreak of a bacterial contagion is a critical threat for human health worldwide. Recently, light-activated heterostructured nanomaterials (LAHNs) have shown potential as antibacterial agents, owing to their unique structural and optical properties. Many investigations have revealed that heterostructured nanomaterials are potential antibacterial agents under light irradiation. In this review, we summarize recent developments of light-activated antibacterial agents using heterostructured nanomaterials and specifically categorized those agents based on their various light harvesters. The detailed antibacterial mechanisms are also addressed. With the achievements of LAHNs as antibacterial agents, we further discuss the challenges and opportunities for their future clinical applications.

Metal nanoclusters (NCs) with unique chemical and physical properties have been extensively demonstrated to be emerging nanoantibiotics for fighting bacterial infections. Understanding the antibacterial mechanisms of metal nanoclusters is important for evaluating their clinical applications as nanoantibiotics. To understand the antibacterial mechanism, gold nanoclusters (AuNCs) were applied as an antibacterial agent for real-time observations of their interactions with bacteria by in situ transmission electron microscopy (TEM). In this work, a surface ligand of glutathione-conjugated (GSH)-AuNCs was prepared via a simple hydrothermal method. Optical and structural characterizations validated the successful preparation of GSH-AuNCs. Bacterial growth curves of Acetobacter aceti revealed that the antibacterial activity of GSH-AuNCs increased with the weight concentration. The antibacterial activity of GSH-AuNCs was confirmed by the intracellular reactive oxygen species (ROS) generation induced by GSH-AuNCs in A. aceti. Furthermore, real-time observations of interactions between GSH-AuNCs and A. aceti were made using in situ liquid cell TEM. Based on the results of real-time observations, GSH-AuNCs first attached onto the bacterial membranes of A. aceti by physical adsorption and then penetrated into A. aceti by internalization. Eventually, the production of intracellular ROS induced by GSH-AuNCs caused destruction of the bacterial membranes, which led to the death of A. aceti. After the bacterial membranes had been destroyed, A. aceti eventually died.

The crystal phase of a nanomaterial can affect its biochemical properties and, as a result, greatly influence its application performance. Transition metal dichalcogenides (TMDs), a group of nanomaterials with the ability to crystallize into distinct crystal phases, show distinct electronic structures which are believed to be material-dependent. Molybdenum disulfide (MoS2) can crystallize into distinct crystal phases of 1T and 2H, and in each of these phases, MoS2 shows completely different and distinct biochemical properties. Although several biochemical properties of MoS2 have been extensively reported, particularly its role as a potent antibacterial agent, exactly how the different crystal phases of MoS2 nanosheets (NSs) influence the nanomaterial’s biochemical performance in the near-infrared (NIR)-I window still remains unknown. Herein, we show through detailed experiments and density functional theory (DFT) simulation of the NIR-based electronic structure–activity relationship of 1T- and 2H-MoS2 NSs exactly how these two distinct phases influence the antibacterial performance at each crystal phase and the different factors involved in this process. We also show how the coordination modes, atomic arrangements, and water adsorption energies of these two crystal phases greatly impact the nanomaterial’s distinct phase properties. 1T-MoS2 NSs are metallic phases with a lower band gap and surface water adsorption energy, while 2H-MoS2 NSs are semiconducting phases; as a result, 1T-MoS2 NSs show superior absorbance in the NIR-I window and hence display a higher photothermal performance and excellent antibacterial effects compared to the semiconducting 2H-MoS2 NSs. Our work shows the factors responsible for the distinct antibacterial behaviors of MoS2 NSs in the two crystal phases. We believe that these findings can be employed in the tunable, effective, and stable nanofabrication of MoS2 NSs as either photothermal agents for cancer cell ablation or as antimicrobial agents.

Global warming and climate change are among the most immediate challenges confronting humans in the 21st century. Artificial photosynthesis represents a promising approach to mitigating the environmental crisis. Recently, people demonstrated that interfacing semiconductor, polymer, or metal-based nanomaterials with specific bacteria can generate built-in artificial photosynthetic systems, enabling solar-to-fuel conversion by forming a basic photosynthetic unit from a network of light-harvesting receptors, molecular water splitting and CO2, or proton reduction machinery. As a cutting-edge research direction, several strategies have been employed to create the artificial photosynthetic biohybrids. Notably, understanding of the molecular basis of these photosynthetic biohybrid systems is the key to improving the solar-to-chemical conversion efficiency. In the current review, we highlight the study of charge uptake channels in biohybrid artificial photosynthetic systems using various nanomaterials and microbes. We emphasize the importance of fully understanding the structures and operating mechanisms of these hybrid systems, as well as the criterion to select suitable microbes and photosensitized nanomaterials.