Infectious diseases associated with medical devices have always been a great challenge in the medical field, seriously threatening the health of patients, and even endangering lives [[1], [2], [3]]. The dynamic interface between the surface of medical implants and the physiological environment near the implant can provide a suitable environment for bacterial adhesion and growth, so microorganisms are liable to colonize on the surface of various medical device materials [4,5]. Antibiotics are commonly used to treat device-related infections, though severe cases may require device removal or replacement. In particular, surgical procedures to replace implants can further exacerbate conditions such as the emergence of secondary infections or antibiotic resistance, leading to increased health cost and patient trauma [6]. Therefore, endowing the implant surface with antibacterial properties is the focus of current research.

The antimicrobial methods of implant surfaces developed by researchers mainly include chemical and physical methods [7]. Chemical methods primarily depend on the release of antibacterial agents (metal ions, organic antimicrobials, antibiotics, etc.), which can effectively eliminate microorganisms colonizing the implant surface during early stages. However, their clinical application is limited by potential toxic side effects and the risk of inducing microbial resistance [8]. Physical methods, on the other hand, create specialized surface structures to inhibit bacterial colonization or kill bacteria mechanically. These approaches circumvent issues of drug resistance and toxicity [9]. Nevertheless, such physical structures often exhibit low antibacterial efficiency and may fail to provide long-term protection against postoperative infections, particularly after biofilm formation [10]. Once a bacterial biofilm develops, its enhanced resilience and strong adhesion to the material surface make eradication significantly more challenging [11]. Therefore, prevention rather than removal of biofilm formation at an early stage of bacterial colonization is highly desirable for dealing with infections in medical implants [12].

Coating the surface of biomedical devices with antimicrobial agents is a preventative measure against nosocomial infections and can provide an avenue for infection prevention. For example, amphipathic polymers are widely used to design antimicrobial coatings [13]. However, since their antibacterial activity mainly relies on strongly positively charged moieties, they are typically quite toxic to host cells. Additionally, such polymer coatings frequently suffer from unstable surface adhesion and a short service life. In this respect, researchers have developed a variety of antimicrobial coatings with strong adhesion using mussel-inspired dopamine as the adhesive layer [14]. Dopamine, which has natural biocompatibility and high adhesion ability, can attach to almost any type of material surface to form stable biomedical functional coatings [15]. Furthermore, as a commonly used photothermal material, dopamine can absorb near-infrared (NIR) light and convert it into heat energy, making it a popular photothermal agent in photothermal therapy (PTT) [16]. Wang et al. reported a cryogel dressing composed of hyaluronic acid and dopamine, which dramatically promotes the healing of infectious wounds due to the inherent antioxidant and hemostatic properties of polydopamine (PDA), as well as its NIR-assisted photothermal antibacterial ability [17].

Generally, when the temperature of PTT is higher than 40 °C, the bacterial vitality will be reduced, and when the temperature exceeds 70 °C, the bacteria will be completely deactivated [18,19]. Since high ambient temperature usually cause damage to normal biological cells, the efficacy of PTT is limited by its temperature range [20]. In order to overcome the defects of onefold PTT therapeutic effect, combining PTT with other therapeutic methods to build a collaborative therapeutic platform has become a momentous pathway [21,22]. For example, Kim et al. developed a metal-organic frameworks (MOF)-derived cobalt-silver bimetallic nanocomposite (Ag@CoMOF) that can continuously release antibacterial metal ions (e.g., Ag and Co ions) in the aqueous phase while exhibiting a strong photothermal conversion effect under NIR irradiation, ultimately demonstrating superior synergistic antibacterial activity [23]. Furthermore, Mu et al. constructed a multimodal synergistic antibacterial system (SNO-CS@MoS2) combining NO gas therapy and PTT triggered by NIR light, which effectively eliminates almost all bacteria in infected wounds while maintaining favorable biosafety and controllability [24]. Phototriggered gas therapy uses the photochemical reactions triggered by a controllable light source to produce gas signal molecules (e.g., CO, H2, H2S) for disease treatment [[25], [26], [27]]. This strategy allows precise control of gas concentration, providing an important approach for improving the safety and controllability of the treatment process [28]. As an endogenous signaling molecule, CO possesses multiple biological functions, but its effects are strictly concentration-dependent [29]. In an appropriate concentration range, CO can exert anti-inflammatory, anti-apoptosis, antihypertensive, vasodilating, anti-atherosclerosis, and cell protection functions [30]. Recent studies have proved that CO can kill drug-resistant bacteria without easily inducing bacterial resistance, making it an increasingly promising solution for addressing antibiotic resistance [31].

In this study, we developed functional nanoparticles (MSN@FeCO) by encapsulating CO donors (Fe3(CO)12, abbreviated as FeCO) within mesoporous silica nanoparticles (MSN). Further, a NIR-triggered antibacterial coating (MSN@FeCO@PDA) was fabricated by immobilizing MSN@FeCO onto a medical catheter surface via PDA, which provides robust adhesion and photothermal properties. Under NIR irradiation, PDA generates localized heat, simultaneously triggering the thermal-responsive release of CO gas from Fe3(CO)12, thereby achieving a synergistic antibacterial effect through combined PTT and CO gas therapy (Scheme 1). We evaluated the photothermal performance of the MSN@FeCO@PDA coating under NIR exposure and characterized the temperature-dependent CO release kinetics. Additionally, the antibacterial efficacy and biocompatibility of the coating were thoroughly investigated.