Dopamine hydrochloride (DA-HCl), bismuth chloride, thioacetamide (TAA), oleylamine, curcumin, Pluronic F127, 1,3,5-trimethylbenzene (TMB), 1,1-diphenyl-2-picrylhydrazyl (DPPH·), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS⁺·), BCA Protein Quantitation Kit, Terephthalic acid (TA) and methyl violet (MV) were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China). These chemicals were of analytical grade and used without further purification.

E. coli (ATCC25922) and S. aureus (ATCC25923) were obtained from China National Institutes for Food and Drug Control (NIFDC). Nutrient Broth (NB) and Agar medium were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. Live/Dead BacLight Bacterial Viability Kit comprising SYTO9 and propidium iodide (PI) were obtained from Beijing labgic technology Co., Ltd. These solutions were prepared using sterile water.

Bi₂S₃ nanoparticles (BS NPs) were synthesized via a reaction between bismuth chloride and thioacetamide, employing standard anaerobic and hot injection techniques [19]. Initially, 63 mg (0.2 mmol) of BiCl₃ was added to 4.0 mL of oleylamine and subjected to vacuum degassing at 70 ℃ for 5 min to remove moisture and oxygen. Subsequently, the reaction vessel was purged nitrogen, and the temperature was ramped up to 150 ℃ at a rate of 10 ℃/min. This temperature was maintained until the BiCl₃ powder was completely dissolved. Thereafter, a solution of TAA in oleylamine (4.0 mL, 0.04 mM) was rapidly injected into the reaction system, and the temperature was further raised to 180 ℃ and held for 5 min. Upon introduction of TAA, the color of reaction mixture rapidly shifted from white to brown, indicating the formation of Bi₂S₃. The growth process of BS NPs was terminated by removing the heat source, followed by cooling down to room temperature. Finally, the resulting precipitate was separated, washed thoroughly, and finally dried in a vacuum oven at 60 ℃.

As depicted in Fig. S1, the Bi₂S₃@MPDA (BSM) nanocomposites were prepared through in-situ surface polymerization. Typically, 10 mg of Bi₂S₃ NPs were redispersed in a 50 mL alcohol/water (V/V = 3/2) mixture, followed by the addition of 190 mg DA-HCl. After stirring for 30 min, 1.0 g of F127 and 1 mL of TMB were introduced into the solution, and the mixture was continuously stirred for an additional hour. Subsequently, the polymerization reaction was initiated by adding 1.21 g of Tris base, and the reaction mixture was stirred at room temperature for 4 h. The resulting products were collected by centrifugation (12000 rpm), and then washed multiple times with an acetone/ethanol (V/V = 1/2) mixture to remove the soft template. The obtained product was vacuum-dried at 60 ℃. Thereafter, the BSM NPs were ultrasonically dispersed in 45 mL of anhydrous ethanol, followed by the addition of a Cur alcohol solution (5 mL, 1 mg/mL). This mixture was gently stirred in the dark for 12 h. Finally, the Bi₂S₃@MPDA-Cur (BSMC NPs) were obtained through centrifugation and freeze-drying.

The morphology and microstructure were characterized via a scanning electron microscope (STM, ZEISS Gemini 300) and a transmission electronic microscope (TEM, JEM-2100). The zeta potential was measured using a Malvern Zetasizer (NanoBrook 90Plus Zeta). The absorption and photoluminescence (PL) spectra were respectively recorded on UV-Visible-Near-Infrared (UV-vis-NIR) spectrometer (Shimadzu UV-2600) and fluorescence spectrophotometer (FP-6500). The functional group information of composites was ascertained by means of Fourier transform infrared spectroscopy (FT-IR, Shimadzu IRTracer-100). The bismuth ion content was determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) on an Agilent ICP-OES5110 instrument. The element and valence states of composites were analyzed by X-ray photoelectron spectra (XPS, Thermo Fisher ESCALAB 250Xi). The photothermal conversion effect was evaluated using a digital thermal imager (FLIR, E50). Finally, bacterial viability was observed using a laser scanning confocal microscope (LSCM, Olympus LEXT OLS4100).

A stock solution of Cur at a concentration of 100 µg/mL was prepared by dissolving Cur in anhydrous ethanol. Subsequently, a series of curcumin standard solutions (5, 10, 20, 40 µg/mL) were obtained through serial dilution of the stock solution. These standards were analyzed using a UV-visible spectrophotometer at 430 nm to generate a calibration curve. The Eq. (1) of the standard curve: y = 0.036x + 0.01698 (R² = 0.9998). 100 µg/mL ethanol solution of BSM and BSMC NPs were sonicated for 2 h to to ensure complete dissolution of Cur. The absorbance of the supernatant was measured at 430 nm, and the corresponding Cur content loaded within the BSM NPs was determined using the standard curve. The drug loading efficiency of Cur was calculated according to the Eq. (2)

Drug load (%) = m_(Cur)/m_(BSMC)×100%

Where m_(Cur) represents the mass of Cur loaded into the BSM NPs, and m_(BSMC) denotes the total mass of the BSMC NPs.

To evaluate the drug release behavior, BSMC NPs were incubated at 37 ℃ in PBS with pH values of 7.4 and 5.0, respectively. At selected time intervals, 2 mL aliquots of the external solution were withdrawn and analyzed spectrophotometrically at 430 nm, then returned back to the medium to keep a constant volume. For NIR light- triggered Cur release, BSMC NPs solutions subjected to NIR laser (808 nm, 1.0 W/cm²) for 10 min, followed by a 30 min interval without irradiation. This cycle was repeated multiple times. The concentration of Cur released from the BSMC NPs was measured at 430 nm using UV-vis spectra. Meanwhile, control experiments were conducted using BSMC NP solutions without exposure to the 808 nm laser. The released Cur concentrations were calculated based on the previously established Cur calibration curve.

The photothermal conversion behaviors of the obtained samples (BS, BSM and BSMC) were investigated under the NIR light (808 nm) irradiation with a laser power density of 1.0 W/cm². Additionally, the BSMC solutions with different concentrations (31.25, 62.5, 125, 250, 500 µg/mL) were exposed to NIR light (808 nm, 1.0 W/cm²) for 10 min. The photothermal stability of the BSMC NPs was further evaluated through four cycles of laser ON/OFF. Throughout these experiment, temperature changes were continuously and thermal images were captured using a thermal infrared camera (E50, FLIR, USA). Detailed methodology for calculating the photothermal conversion efficiency (η) is provided in the Supporting Information.

The ROS generation capacity of the BSMC sample was evaluated using terephthalic acid (TA) as a probe. In the presence of hydroxyl radical, terephthalic acid (TA) is efficiently converted into a fluorescent compound, 2-hydroxyterephthalic acid (TAOH), with the fluorescence intensity of TAOH being directly proportional to the hydroxyl radical concentration. Initially, 5 mg of the BSMC NPs were dispersed into PBS solution of TA (3 mL 0.5 mM) in darkness at an ice bath, followed by exposure to 808 nm laser for a predetermined period. The fluorescence emission peak of TAOH at 435 nm was subsequently recorded using a fluorescence spectrometer.

Additionally, methyl violet (MV) was employed as an additional indicator to quantify ROS levels, where the degradation rate of MV exhibited a linear relationship with hydroxyl radical concentration. For this assay, 1 mg of the BSMC sample was dispersed in 3 mL of MV (0.05 mM) solution and maintained in a dark ice bath for 30 min to achieve the adsorption-desorption equilibrium. Subsequently, the mixed solution was irradiated with an 808 nm laser for intervals of 5, 10, 15, and 20 min. At each time point, aliquots of the supernatant were collected, and the absorbance at 580 nm was measured using a UV-visible spectrophotometer.

The antioxidant activity of BSMC NPs was evaluated by measuring their scavenging activity against DPPH· and ABTS⁺· free radical. For the DPPH assay, the BSMC NPs solutions with different concentrations were incubated with 0.1 mM methanolic DPPH solution for 30 min in the dark, after which the absorbance was measured at 517 nm using a UV-vis spectrophotometer. In the ABTS assay, 0.035 mM potassium persulfate was mixed with 0.1 mM ABTS in an aqueous medium and allowed to react for 12 h in the dark to generate the ABTS⁺· radical. Subsequently, BSMC NPs solutions were added to this mixture and incubated for 30 min, and the corresponding absorbance was recorded at 734 nm. The antioxidant activity was quantified using the following equation:

Antioxidant activity (%) = (Ac- As)/Ac×100%

Where Ac and As denote the absorbance values of the control and test group, respectively, for either the DPPH or ABTS assays.

The antimicrobial efficacy of the synthesized materials was evaluated against two pathogenic bacterial strains, E. coli and S. aureus. Initially, these strains were cultured overnight in standard nutrient broth at 37 ℃. Subsequently, a diluted suspension of either S. aureus or E. coli (100 µL, 1 × 10⁸ CFU/mL) was combined with 900 µL of culture medium solution containing different samples. This mixture was then exposed to NIR laser (808 nm, 1.0 W/cm²) for 10 min, followed by incubation at 37 ℃ for several hours. Thereafter, the co-cultured suspension was serially diluted and evenly spread onto agar plates. Finally, bacterial colony-forming units were counted and photographed after incubating at 37 ℃ for 24 h.

The BCA protein assay was employed to detect the protein leakage from E. coli and S. aureus subjected to light exposure. Initially, the bacterial stock solution was centrifuged at 6000 rpm for 5 min at 4 ℃, and the supernatant was discarded. The resulting bacterial pellets were washed three times with PBS and subsequently diluted to an OD600 value between 0.02–0.1. The diluted bacterial suspensions were thoroughly mixed with the synthesized material within an EP tube at a ratio of 1:1 (100 µL + 100 µL). These mixtures were exposed to NIR laser for 5, 10 or 15 min, followed by centrifugation. Subsequently, 25 µL of the supernatant was mixed with 200 µL of BCA working solution and incubated at 37 ℃ for 30 min. Finally, the absorbance at 562 nm (OD562) was measured to determine the extent of protein release.

Bacterial samples treated with as-obtained materials (BS, BSM and BSMC) were exposed to NIR laser at an intensity of 1.0 W/cm² for 10 min, followed by co-culturing for 24 h. Subsequently, the bacterial suspensions were centrifuged at 10000 rpm and washed with PBS (0.01 M, pH 7.4). The bacteria were then stained with SYTO9 and PI, and incubated in the dark on a shaker for 20 min. SYTO9 selectively stains viable cells with green fluorescence, whereas PI labels non-viable cells with red fluorescence. Bacterial viability was assessed using confocal laser scanning microscope (CLSM).

All experiments were performed in three times, and the results were presented as the mean ± SD (standard deviation). The statistical method was conducted with ANOVA and Student’s t-test (*p < 0.05, **p < 0.01, and ***p < 0.001).

The BSM NPs were prepared via emulsion-induced interface polymerization of DA combined with a sacrificial template approach, wherein F127 and TMB functioned as organic templates and Tris base served as the catalyst [20]. As depicted in Fig. 1a and b, the particle size of BSM NPs was approximately 80 nm. And besides, the spherical mesoporous structure (Fig. S2) of the BSM NPs was confirmed, which provide an effective framework for drug encapsulation. SEM and TEM images (Fig. 1c, d) revealed that the synthesized BSMC NPs were uniform, spherical, and ranged from 80 to 90 nm in diameter. Notably, compared to BSM NPs, the average particle size of BSMC NPs exhibited a slight increase, accompanied by alterations in surface morphology and a marked reduction in mesoporous structure, indicative of successful Cur loading. The elemental mapping images (Fig. 1e) confirms the presence and homogeneous distribution of Bi, S, N and O elements. The EDX spectrum analysis (Fig. S3) revealed a Bi weight percentage of 14.86%, substantially exceeding that of S (0.64%) in BSMC, suggesting that dopamine coordinates with bismuth ions, partially replacing the sulfur. Additionally, the content of Bi in BSM NPs was quantified as 15.09% using inductively coupled plasma optical emission spectroscopy (ICP-OES), which is basically consistent with the EDX results.

X-ray photoelectron spectroscopy (XPS) was further employed to analyze the chemical composition of BSMC NPs. As illustrated in Fig. 2a, the XPS survey spectrum demonstrated the presence of Bi, S, N, C, and O elements, which is consistent with the EDX spectrum and elemental mapping results. The high-resolution Bi 4f spectrum (Fig. 2b) exhibited characteristic peaks at binding energies of 158.6 eV and 164.1 eV, corresponding to Bi 4f7/2 and Bi 4f5/2 states of Bi³⁺, respectively [21]. In the deconvoluted S 2p high-resolution spectrum (Fig. 2c), the two peaks at 164.0 eV and 165.6 eV were assigned to S 2p3/2 and S 2p1/2 of S22- species, respectively [22]. The high-resolution spectrum of C1s (Fig. 2d) was resolved into three sub-peaks: the peak near 284.4 eV attributed to benzene carbon atoms, and peaks at 285.9 eV and 288.0 eV corresponding to C-N and C = O bonds, respectively, indicative of successful incorporation of dopamine and curcumin [23]. The N1s spectrum (Fig. 2e) displayed a peak at 399.4 eV, characteristic of pyrrolic nitrogen in MPDA [24]. In terms of the O1s high-resolution spectrum (Fig. 2f), the two peaks at 532 .3 eV and 531.0 eV corresponded to C-O and S = O bonds, respectively [25]. Collectively, these spectroscopic results confirm the successful synthesis of the BSMC nanocomposite.

The zeta potential measurements were performed to monitor the synthesis process. As shown in Fig. 3a, the bare Bi₂S₃ NPs exhibited a positive surface charge with zeta potential of 15.40 mV. Following coating with MPDA, the zeta potential shifted to a negative value of -34.72 mV, attributable to the abundant hydroxyl groups present on the polydopamine surface. Subsequent loading of curcumin onto the BSM NPs further increased the negative charge to -38.41 mV, consistent with the anionic nature of curcumin and confirming successful drug loading [26]. Fourier-transform infrared (FT-IR) spectroscopy provided additional evidence for the material composition. As shown in Fig. 3b, the Bi₂S₃ spectrum displayed a characteristic peak of Bi-S bond at 542 cm⁻¹ [27]. Two distinct bands at 2857 and 2921 cm⁻¹ were attributed to N–H and O–H stretching vibrations, likely originating from the residual raw material TAA [28]. The absorption peaks of the BSMC at 1608, 1510 and 1281 cm^− 1 were attributed to stretching vibrations of C = O and C = C double bonds and aromatic C–O stretching of curcumin and MPDA, respectively [29]. Moreover, the phenol hydroxyl stretching vibration observed at approximately 3500 cm^− 1 in both Cur and BSM spectra was markedly diminished in the BSMC spectrum, suggesting hydrogen bonding interactions between curcumin and MPDA [30]. These spectral features confirm the successful fabrication of the BSMC nanoparticles.

The N₂ adsorption-desorption isotherms of BSM and BSMC NPs are presented in Fig. 3c, displaying typical type IV curves characteristic of mesoporous materials. The specific surface areas (S_BET) of BSM and BSMC NPs were determined to be 51.4 and 30.1 m²/g, respectively, with corresponding average pore diameters of 30.8 and 4.2 nm. Compared with BSM NPs, BSMC NPs exhibited a significant reduction in both specific surface area and pore size, likely attributable to curcumin occupying the partial mesoporous voids. The curcumin loading capacity was quantified via a standard curve method. As shown in Fig. 3d, the drug loading efficiency increased with the Cur-to-BSM feeding ratio increase, reaching approximately 35.0% at a mass ratio of 2.5:1. Beyond this ratio, further increases in Cur content resulted in only marginal enhancements in loading efficiency, indicating that curcumin accumulation on the surface of MPDA approached saturation.

To simulate both the acidic environment of wound sites and the physiological conditions of normal tissue, the Cur release experiments were conducted in PBS at pH 5.0 and 7.4, respectively. The release profile (Fig. 3e) demonstrated that 24.9% and 51.2% of Cur were released at 12 h and 48 h under weakly acidic conditions (pH 5.0), whereas only 18.6% and 25.1% of Cur were released at the corresponding time points under normal physiological conditions (pH 7.4), indicating that the wound microenvironment facilitates the release of curcumin. Furthermore, the NIR laser irradiation influenced Cur release through a photothermal effect (Fig. 3f). Specifically, the cumulative Cur release reached 8.4% under NIR irradiation after 240 min, compared to 4.1% without laser exposure. Collectively, these results indicate that both the acidic wound microenvironment and photothermal stimulation are conducive to Cur release, potentially enabling synergistic photothermal-chemotherapeutic treatment of wound infections [31].

As shown in Fig. 4a, bare Bi₂S₃ exhibited a low absorption capacity in the near infrared region, whereas the absorption intensity within the NIR range was significantly enhanced for BSM and BSMC NPs. This enhancement was attributed to the presence of a conjugated system and an electron donor-acceptor structure within the MPDA component, which effectively improve the light-harvesting efficiency of the composite nanomaterials. The broad absorption spectrum of BSMC facilitates efficient photothermal conversion, enabling the effective transformation of absorbed light into thermal energy. Subsequently, the photothermal conversion behaviors of these nanomaterials were investigated under NIR light irradiation. As depicted in the temperature profiles and corresponding photothermal images (Fig. 4b,c), upon 808 nm NIR irradiation for 10 min, the temperature of BS, BSM, and BSMC NPs reached 26.2 ℃, 50.4 ℃, and 49.1 ℃, respectively. Notably, the temperature elevation observed for BSMC NPs was slightly lower than that of BSM NPs, which may be attributed to the reduced proportions of the core photothermal components, MPDA and Bi₂S₃, following the incorporation of Cur. The temperature of the BSMC NPs solution exhibited a positive correlation with laser power density (Fig. 4e), and the photothermal response was also dependent on both nanoparticle concentration and irradiation duration. Specifically, the temperature of BSMC solution increased from 26.6 ℃ to 48.8 ℃ as the concentration varied from 0 to 500 µg/mL (Fig. 4d). In order to assess the photothermal stability of BSMC NPs, the heating-cooling cycles were conducted over four consecutive NIR irradiation periods. As depicted in Fig. 4f, the photothermal cycle curve remained relatively unchanged after four cycles, indicating excellent photothermal and chemical stability. Finally, the photothermal conversion efficiency (𝜂) of the BSMC NPs was calculated to be 35.2% (Fig. S4), which was remarkably higher than those reported for other melanin-based materials and Bi₂S₃ semiconductor photocatalysts [32].

Photothermal agents not only induce localized high temperatures but also generate a substantial quantity of reactive species [33]. The sharp increase in reactive species can lead to oxidative stress within cells, thereby damaging infected lesions and eliciting localized inflammatory responses [34]. Consequently, the removal of excess ROS and the regulation of oxidative stress are essential for mitigating oxidative damage and inflammation [35]. The ROS scavenging capacity of BSMC was evaluated by the DPPH· and ABTS⁺· methods. DPPH·, a stable nitrogen-centered radical exhibiting a purple coloration in aqueous solution, can be reduced by antioxidants through the donation of hydrogen atoms or electrons, resulting in the formation of colorless DPPH-H and a corresponding decrease in absorbance at 517 nm [36]. As depicted in Fig. 5a and c, the absorbance gradually decreased with increasing concentrations of BSMC, and the scavenging rate reached 99.1% at 100 µg/mL. In addition, the ABTS⁺· scavenging assay also showed similar results to the DPPH experiment (Fig. 5b and d). The absorption peak of green ABTS⁺⋅ radicals at 734 nm was gradually diminished in a concentration-dependent manner, achieving a scavenging rate of 72.5% at 100 µg/mL. These findings suggest that BSMC exhibits rapid free radical scavenging capabilities and possess significant antioxidant activity.

The antimicrobial efficacy of nanomaterials was assessed using Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus through the plate method. As depicted in Fig. 6, there were no detectable alterations in the colony counts neither the blank group (sample-free and light-free) nor the control group (only light), indicating that the laser irradiation had negligible impact on bacterial viability. Moreover, the bacterial colony growth in the BS group was comparable to that in the control group. A substantial number of colonies were observed in both the BSM and BSMC groups in the absence of NIR irradiation, demonstrating the favorable biocompatibility and biosafety of the BSM and BSMC NPs. Notably, the antibacterial ability of the BSMC group was significantly enhanced following NIR light exposure, and the inhibition rates against E. coli and S. aureus reached up to 92.4% and 98.5%, respectively. In addition, the antibacterial activities of BSMC NPs at different concentrations were also investigated (Fig. S5), and the antibacterial effect exhibited significant concentration-dependent and NIR-dependent characteristics. These results validated that the superior antibacterial performance of BSMC NPs results from the synergistic interaction between curcumin and light irradiation. Interestingly, the inactivation rate of S. aureus exceeded that of E. coli in this study, contrasting with previous reports [37]. This discrepancy may be attributed to the greater resistance of Gram-negative bacteria to the phototoxic effects of curcumin compared to Gram-positive bacteria [38].

In addition, the photothermal antibacterial activity of BSMC NPs was further evaluated using a live/dead double staining assay. SYTO9 and PI, both exhibiting strong DNA-binding properties, are widely utilized in bacterial viability assessments. SYTO9 readily penetrates intact bacterial membranes and binds to DNA, producing green fluorescence, whereas PI can only infiltrate damaged bacterial cell membranes, binding to DNA and emitting red fluorescence [39]. As illustrated in Fig. 7, the control group demonstrated intense green fluorescence, indicative of high bacterial viability. Treatment with BS and BSM NPs resulted in diminished green fluorescence alongside the emergence of red fluorescence, suggesting partial disruption of bacterial membranes. Notably, exposure to BSMC NPs led to a marked reduction in green fluorescence coupled with pronounced red fluorescence, signifying extensive bacterial membrane damage and near-complete bacterial inactivation. These observations are consistent with the bacterial survival rates determined via the plate counting method.

In general, the photothermal bactericidal processes are attributed to the photoinduced generation of reactive species, including holes (h⁺), electrons (e⁻), superoxide radicals (·O₂⁻), and hydroxyl radicals (·OH), mediated by antibacterial agents [40]. The substantial elevation in reactive oxygen species (ROS) induces oxidative stress within bacterial cells, resulting in damage to the bacterial cell membrane and subsequent leakage of intracellular components such as DNA, RNA, and proteins. To quantify ROS production, terephthalic acid (TA) and methyl viologen (MV) reagents were employed as probes. Firstly, TA is used as a fluorescent probe to detect the generation of ·OH. In the presence of ·OH, TA is oxidized to TAOH, and the fluorescence intensity of TAOH is positively correlated with the level of ·OH. As shown in Fig. 8a, the control group (TA alone) exhibited negligible fluorescence, while the TA/BSMC and TA/BSMC/H₂O₂ groups showed minimal fluorescence in the absence of NIR irradiation. However, the fluorescence intensity in the TA/BSMC/H₂O₂ group increased significantly with prolonged NIR exposure, suggesting enhanced TAOH formation and, by extension, elevated free radical generation. Complementarily, MV, a UV-visible absorption probe, was further utilized to detect the generation of reactive species. MV undergoes oxidation to smaller molecules, and the corresponding decrease in its absorption peak at 580 nm associated positively with free radical concentration. As shown in Fig. 8b, the absorbance of MV diminished progressively with increasing illumination time, reflecting gradual MV degradation and concomitant ROS production. These results indicate that infrared light irradiation stimulates free radical generation.

The generated ROS can oxidize phospholipids and membrane proteins within the bacterial cell membrane, thereby increasing membrane permeability. Damage to the bacterial membrane facilitates the efflux of small molecules such as K⁺, PO₄³⁻, DNA, and RNA. Among them, DNA and RNA exhibit characteristic absorption peaks at 260 nm in the ultraviolet-visible spectrum; thus, optical density measurements at 260 nm (OD₂₆₀) serve as an indicator of nucleic acid leakage and bacterial membrane integrity [41]. As depicted in Fig. 8c-d and Fig. S6, OD₂₆₀ values increased progressively with extended exposure time, signifying cumulative membrane damage and enhanced nucleic acid release. Beyond that, protein leakage from S. aureus and E. coli was assessed using the bicinchoninic acid (BCA) protein assay. Under alkaline conditions, the leaked proteins can reduce divalent copper ions (Cu²⁺) to monovalent copper ions (Cu⁺), which subsequently form a purple complex with the BCA reagent [42]. The absorbance at 562 nm exhibits a strong linear correlation with protein concentration across a broad range. As depicted in Fig. 8e-f, absorbance at 562 nm increased gradually with prolonged light exposure for both bacterial strains, corroborating the progressive release of intracellular proteins.