Globally, bacterial infections have always posed a major health threat, and have placed a huge burden on public health, both economically and in terms of maintaining effective protective agents [1]. Although much progress has been made in artificial antibacterial agents and their application, bacteria still pose a great clinical challenge [2], [3], [4]. Antibiotics are generally used to treat bacterial infectious diseases, which can not only disrupt the immune system, but also give rise to bacterial resistance and even the emergence of superbacteria [5], [6], [7], [8], [9]. Therefore, it is imperative to develop safe and efficient solutions without antibiotics for the treatment of diseases caused by bacteria.

Photodynamic therapy (PDT), which relies on the reactive oxygen species (ROS) produced by semiconducting nano-agents under illumination, is considered an outstanding alternative for the antibiotic-free cure of bacterial infections [10], [11]. This approach offers a broad antibacterial spectrum with non-invasiveness through redox reactions at the nano-biointerface [12]. However, although many photocatalytic antibacterial agents have been developed, besides potential biotoxicity, most systems, such as those based on TiO2, still suffer from rapid recombination of photogenerated charge carriers and weak light absorption, making them unsatisfactory for practical application [13]. Hence, it is still a tremendous challenge to devise efficient photocatalytic antibacterial materials with excellent biosafety.

Recently, Bi-based 2D nanosheets have become a hot topic in photocatalytic antibiosis due to their favorable chemical and optical properties and lower susceptibility to bacterial resistance [14], [15], [16], [17], [18]. Unfortunately, single-component Bi-based semiconductors are extremely limited with regard to practical application due to a wide band gap and rapid recombination of photo-generated charge carriers, leading to suboptimal photocatalytic performance in facilitating ROS generation. Therefore, various approaches, such as heteroatom doping [19], defect formation [20], and heterojunction formation [21] by coupling plasmonic nanostructures with semiconductors, have been applied to render them more responsive to light. In this context, localized surface plasmon resonance (LSPR) has emerged as a favorable solution for promoting photocatalytic antibacterial performance [22], enhancing light absorption [23], and inhibiting photogenerated charge carrier recombination [24]. LSPR occurs on the surfaces of metal nanostructures, such as those of gold [25], silver [26], copper [27], and bismuth [28], and offers potential for antibacterial phototherapy through plasmonic energy transfer from the metal nanostructure to the semiconductor [29]. For instance, Shi et al. reported that a system of Ag quantum dots (QDs)/Bi4O5Br2 showed better photocatalytic disinfectant ability than pure Bi4O5Br2, effectively eradicating Escherichia coli (1 × 107 CFU/mL; CFU = colony forming units) upon visible light exposure for 180 min [30]. Although the photocatalytic properties of Bi-based semiconductors have been somewhat enhanced, they are still hampered by possible biotoxicity, high cost, low interfacial charge-transfer/separation efficiency, and the need for a precious metal. This is due to lattice mismatch between the Bi-based semiconductor and the noble metal [31], which leads to severe charge recombination and poor carrier utilization [32]. Therefore, there is great demand to devise an effective and biosafe method for establishing Bi-based plasmonic heterojunctions with appropriate atomic level contact to enhance photocatalytic antibiosis.

Very recently, we found that an atom co-sharing Bi/Bi4O5Br2 nanomaterial heterojunction shows much higher photodegradation efficiency of bisphenol A (BPA) than a pure Bi4O5Br2 nanosheet under simulated sunlight irradiation [33]. It thus has great potential as a novel nano-agent for PDT. However, the biosafety and visible-light-driven photocatalytic antibacterial activity of the atom co-sharing heterojunction has yet to be fully explored. Encouraged by the above work, a Bi atom co-sharing Bi/Bi4O5Br2 plasmonic heterojunction was prepared by a simple hydrothermal in situ construction method for photocatalytic antibiosis. The obtained system shows good biocompatibility and high photocatalytic sterilization efficacies of 98.5 % towards Escherichia coli (E. coli) and 94.1 % towards Staphylococcus aureus (S. aureus) in 60 min. This makes it promising for the treatment of human and animal diseases caused by bacteria.