ZIF-8 was synthesized through a specific coordination reaction between zinc ions and 2-methylimidazole. In a typical experiment, 1.069 g Zn(NO₃)₂·6H₂O was dissolved in 15 mL of DMF-MeOH mixture (v/v = 4:1) as solution 1, 1.161 g of 2-methylimidazole was dissolved in 10 mL of DMF-MeOH (v/v = 4:1) as solution 2; then, solution 1 was added to solution 2 and kept stirring vigorously overnight. Subsequently, the milky product was collected by centrifugation at 14,000 rpm for 10 min, rinsed with methanol and ultrapure water two times, and then dried at 80°C overnight to obtain ZIF-8 for subsequent experiments.

ZIF-8@PDA was attained by a self-polymerization reaction of dopamine. A measure of 20 mg ZIF-8 we prepared was dissolved in the Tris-HCl buffer solution (pH 8.5, 50 mM) with the assistance of sonicating for 2 min; then, 10 mg dopamine was added to the above solution, and the mixture was violently stirred for 90 min. Thereafter, the obtained black mixture was collected by centrifugation at 14,000 rpm for 10 min, washed with water three times, and eventually concentrated to 2 mL for later use.

Subsequently, ZIF-8@PDA@Pt was gained by an in situ reduction method using ZIF-8@PDA as a precursor. A measure of 2 mL of ZIF-8@PDA we prepared previously was added to 7,740 μL ultrapure water and sonicated for 2 min; then, 260 μL of H₂PtCl₄ (19.2 mM) was added and sonicated for 5 min; in a rapid subsequence, 500 μL of the refresh NaBH₄ solution (1 M) was added to the above solution under drastic magnetic stirring for 1 h. Finally, the mixture was collected by centrifugation at 14,000 rpm for 10 min and ultimately washed with ultrapure water three times to obtain ZIF-8@PDA@Pt.

The peroxidase-mimic activity of ZIF-8@PDA@Pt was measured by a classical chromogenic reaction using TMB as the substrate. In brief, 5 μL TMB (80 mM), 50 mL H₂O₂ (10 mM), and 50 μL ZIF-8@PDA@Pt (0.2 mg mL⁻¹) were added to the phosphate buffer solution (pH 5.0, 20 mM) with a total volume of 0.5 mL, respectively. Subsequently, the mixture was incubated for 5 min, and the absorbance at 652 nm was recorded simultaneously by an ultraviolet-visible spectrum. o-Phenylenediamine (OPD) was employed as a chromogenic substrate to further evaluate the peroxidase-mimic activity of ZIF-8@PDA@Pt. Typically, 5 μL OPD (50 mM), 50 mL H₂O₂ (10 mM), and 50 μL ZIF-8@PDA@Pt (0.2 mg mL⁻¹) were added to the phosphate buffer solution (pH 5.0, 20 mM) with a total volume of 0.5 mL, respectively. Subsequently, the mixture was incubated for 5 min, and the absorbance at 425 nm was recorded simultaneously by an ultraviolet-visible spectrum.

The kinetic assay of the peroxidase-mimic activity of ZIF-8@PDA@Pt was conducted by changing the concentration of H₂O₂ or TMB. The reaction was performed under an optimized condition (pH 5.0, 37°C). Typically, 2 μL TMB (80 mM), H₂O₂ with different concentrations, and 20 μL ZIF-8@PDA@Pt (0.2 mg mL⁻¹) were added to a phosphate buffer solution (pH 5.0, 20 mM) with a total volume of 0.2 mL; then, the absorbance at 652 nm was recorded in time at a time scanning window. The real-time velocity of the reaction was converted by the Beer–Lambert Law, A = εbC, where b is the path length (1 cm) and ε is the molar absorption coefficient of oxidized TMB (39,000 M⁻¹ cm⁻¹). Corresponding parameters of kinetics were calculated according to the Michaelis–Menten equation and Lineweaver–Burk plot: V 0 = V max S S +   K m , 1 V 0 =   K m V max   1 S + 1 V max , where V ₀ is the initial reaction rate and [S] is the concentration of the substrate (H₂O₂ or TMB).

Terephthalic acid (TA) was used as a fluorescent probe to validate the generation of •OH. Typically, TA (0.5 mM), H₂O₂ (2 mM), and ZIF-8@PDA@Pt (0.1 mg mL⁻¹) were first mixed into PBS (pH = 5.0, 20 mM) and incubated in dark for 2 h, and then were taken for fluorescent spectra characterization. In addition, 1,3-diphenylisobenzofuran (DPBF) and 9,10-anthracenediyl-bis(methylene)-dimalonic acid (ABDA) were used as probes to assay O₂ ^•− and ¹O₂, respectively. Specifically, DPBF (1 mM), H₂O₂ (2 mM), and ZIF-8@PDA@Pt (0.1 mg mL⁻¹) were incubated together in PBS (pH = 5.0, 20 mM) for 5 min; meanwhile, the absorbance at 421 nm was recorded every 30 s. ABDA (0.05 mM), H₂O₂ (2 mM), and ZIF-8@PDA@Pt (0.1 mg mL⁻¹) were incubated together in PBS (pH = 5.0, 20 mM) for a while and then were taken to measure the change of absorbance using UV spectra.

The photothermal property of ZIF-8@PDA@Pt was determined using an 808-nm laser, and the real-time temperature was observed with a thermal imaging camera. In brief, ZIF-8@PDA@Pt aqueous dispersion with different concentrations (0, 20, 40, 60, 80, 100, and 120 ug mL⁻¹) was radiated under 808 nm (1.0 W cm⁻¹) for 5 min. Concurrently, the temperature of the ZIF-8@PDA@Pt aqueous dispersion was recorded every 30 s. Thereafter, the heating–cooling curves were obtained to calculate the photothermal conversion efficiency in accordance with below equations: η = h S   T max   ‐   T surr   ‐   Q 0 I   1   ‐   10 ‐ A 808 , (1) τ s = m d C d h S , (2) Q 0 = h S   T max ⁡ , water   ‐   T surr , (3) where η is the photothermal conversion efficiency. The value of τ _s was obtained by linearly fitting the plot of the cooling time t versus the term -Lnθ, hS was obtained from Eq. 2, m _d is the mass of the solution (0.2 g), C _d is the heat capacity of water (4.2 J g⁻¹°C⁻¹), Q₀ was obtained from Eq. 3, T _max is the equilibrium temperature (61.5°C), T _{max, water} is the maximum temperature of water (29.1°C), and T _surr is the surrounding ambient temperature (28.3°C). I is the incident light power (0.8 W cm⁻²), and A₈₀₈ is the absorbance of the ZIF-8@PDA@Pt aqueous dispersion (120 μg mL⁻¹) at 808 nm (0.17).

Staphylococcus aureus and Escherichia coli were selected as Gram-positive and Gram-negative model strains to estimate the antibacterial activity of ZIF-8@PDA@Pt, respectively. Mono colonies of S. aureus and E. coli on a solid agar plate were first transferred to 2 mL of the lysogeny broth (LB) medium and shaken at 37°C for 12 h at 150 rpm. Four different groups were set in this typical procedure, containing I: Control, II: H₂O₂, III: ZIF-8@PDA@Pt + H₂O₂, and IV ZIF-8@PDA@Pt + H₂O₂ + NIR. In addition, 0.3 was selected as the initial optical density of bacteria at OD_600 nm. In addition, the final concentration of H₂O₂ and ZIF-8@PDA@Pt in the incubation system was 2 mM and 100 μg mL⁻¹, respectively. All groups were incubated at 37°C for 20 min. Thereafter, the bacterial suspensions were moved to the solid medium by the spread plate method and cultured at 37°C for another for 12 h. Finally, all experimental groups were taken for imaging and counting. Each assay was performed in triplicates.

Bacterial suspensions treated with the different experimental conditions were first centrifuged for 5 min (4,000 rpm), followed by washing two times using 0.85% NaCl solutions. Afterward, the above bacterial suspensions were stained with SYTO 9 and propidium iodide and then observed with a fluorescent microscope.

HSF cells were performed for the biocompatibility assay of ZIF-8@PDA@Pt. At first, the HSF cells were cultured in a 96-well plate (8,000 cells per well) at 37°C for 24 h; then, ZIF-8@PDA@Pt with different concentrations (0, 25, 50, 100, 150, and 200 μg mL⁻¹) were added to the above medium and incubated for another 24 h at 37°C. Thereafter, 10 μL of the MTT solution was added to every well. After 4 h, the medium was extracted and 150 μL of DMSO was added to every well. The cell viability was assayed using a microplate reader.

ZIF-8@PDA@Pt was prepared through in situ reduction of H₂PtCl₄ in the presence of a specific precursor obtained by modifying a layer of polydopamine on the surface of ZIF-8. To begin with, ZIF-8 was conducted by a specific coordination reaction between zinc ions and 2-methylimidazole. Afterward, a layer of PDA was modified on ZIF-8, relying on the self-polymerization reaction of dopamine under a weak alkaline environment to obtain ZIF@PDA. Eventually, Pt NPs were localized on ZIF@PDA by in situ reduction to obtain the nanozyme ZIF-8@PDA@Pt. TEM and SEM were primarily employed to characterize the morphology during the formation of ZIF-8@PDA@Pt (Figures 1A, B); it is clearly to be observed that ZIF-8 possesses the regular rhombic dodecahedral morphology while a thin layer at the edge of ZIF-8 was noticed after modifying polydopamine, verifying the formation of ZIF-8@PDA. In addition, it can be seen that ultra-small Pt NPs were distributed on ZIF-8@PDA. In addition, energy-dispersive X-ray spectrometry (EDX) mapping was recruited to characterize the elemental distribution of ZIF-8@PDA@Pt nanozyme (Figure 1C). The results presented the homogeneous distributions of elements C, N, O, Zn, and Pt in ZIF-8@PDA@Pt, demonstrating the successful loading of Pt NPs onto the ZIF-8@PDA platform. Meanwhile, ZIF-8@PDA@Pt exhibits a size of approximately 650 nm, according to the dynamic light scattering analysis (Figure 1D).

Additionally, in order to explore the chemical structure and composition, we executed X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis spectra. As illustrated in Figure 1E, the pattern of ZIF-8 exhibits several typical characteristic peaks at around 7.46°, 10.52°,12.87°, and 18.27°, ascribing to (001), (002), (112), and (222) crystal faces, respectively, which conforms its regular crystal structure. Of note, the main diffraction peaks of ZIF-8 remained after modifying PDA and loading Pt NPs. In particular, the XRD diffraction of ZIF-8@PDA@Pt presents an unmistakable peak at 39.5° in line with the (111) facet of the Pt crystal (JCPDS No. 04-0802), which further confirmed the successful preparation of ZIF-8@PDA@Pt. The UV-vis spectra were also measured and are presented in Figure 1F. It can be noted that two typical peaks at approximately 234 and 300 nm in ZIF-8 and ZIF-8@PDA assigned to the π-π* transition of the conjugated system from the imidazole structure and n-π* transition of polydopamine, respectively. Nonetheless, the peak at approximately 300 nm is not well-preserved in ZIF-8@PDA@Pt, which may be caused within the loading of Pt NPs. In addition, XPS was performed to characterize the element constitution of ZIF-8@PDA@Pt (Supplementary Figure S1). The element contents of C, N, O, Zn, and Pt are 53.08%, 9.55%, 25.03%, 10.72%, and 1.62%, respectively. More precisely, in the high-resolution spectrum of Pt 4f, the peaks located at 71.0, 72.2, 74.2, and 75.5 eV are ascribed to Pt⁰ 4f 7/2, Pt⁴⁺ 4f 7/2, Pt⁰ 4f 5/2, and Pt⁴⁺ 4f 5/2 binding energies, respectively, which are analogous to the majority of Pt NPs. Likewise, several typical peaks at approximately 284.5, 286.2, and 288.3 eV can be identified from the high-resolution C1s spectrum, which are assigned to C-C, C-N/C-O, and C=C groups, respectively. It can be observed that three peaks are located at 398.2, 399.3, and 400.7 eV from the N 1s spectrum, corresponding to pyridinic N, pyrrolic N, and graphitic N, respectively. Comparably, the curve-fitted O1s spectrum exhibits two peaks 531.3 and 533.1 eV, attributing to C-O and C-OH groups, respectively. In addition, the high-resolution Zn 2p spectra of ZIF-8@PDA@Pt present two peaks placed at 1022.3 and 1045.3 eV belonging to Zn 2p 1/2 and Zn 2p 2/3 of zinc oxide, respectively. In combination with the above results, it is believed that ZIF-8@PDA@Pt was successfully prepared.

After successful synthesis of the ZIF-8@PDA@Pt nanoparticles, we then investigated its peroxidase (POD)-like activity using 3,3′,5,5′-tetramethylbenzidine (TMB) as the chromogenic substrate and H₂O₂ as the catalysis substrate. As shown in Figure 2A, without ZIF-8@PDA@Pt, H₂O₂ cannot cause any color change in the TMB solution. However, in the presence of ZIF-8@PDA@Pt and H₂O₂, the color of the TMB solution significantly changed to dark blue (Figures 2A–2iv), indicating the strong POD-like activity of ZIF-8@PDA@Pt. In this catalytic system, ZIF-8@PDA@Pt may catalyze H₂O₂ to produce ROS, which can oxidize TMB to generate blue color. Notably, without H₂O₂, the nanozyme ZIF-8@PDA@Pt can also cause an obvious change in the color of the TMB solution (Figures 2A–2iii), demonstrating that the nanozyme also possesses oxidase-like activity. The enzyme-like activity of ZIF-8@PDA@Pt was also demonstrated from the absorbance change of the TMB solution (Figure 2B). To further evaluate the enzymatic activities of the nanozyme ZIF-8@PDA@Pt, the catalytic dynamics was investigated. We carried out a steady-state kinetic study to obtain the rate constants by varying the concentration of TMB with a constant concentration of H₂O₂ or vice versa. The Michaelis constant (K _m ) and maximum reaction rate (V _max) were calculated from the fitted Michaelis‒Menten curves and Lineweaver‒Burk double reciprocal plots (Figures 2C–F). As a comparison, the obtained K _m and V _max of ZIF-8@PDA@Pt and other catalysts including the natural enzyme HRP and Fe₃O₄ nanozymes are listed in Supplementary Table S1. K _m indicates the enzyme affinity toward substrates, and V _max defines the maximal catalytic capacity of an enzyme under specified conditions. Generally, a smaller K _m demonstrates higher affinity, while the higher V _max refers to the better catalytic capability. These results indicated that the obtained nanozyme ZIF-8@PDA@Pt shows better catalytic performance than the classical POD nanozyme Fe₃O₄, and some parameters are even significantly better than natural enzymes. For example, K _m of ZIF-8@PDA@Pt was 0.062 mM for TMB, which is much lower than that of HRP and Fe₃O₄, indicating that ZIF-8@PDA@Pt has the highest enzyme affinity toward TMB. Moreover, ZIF-8@PDA@Pt also shows the highest V _max values. These results demonstrated that the obtained ZIF-8@PDA@Pt possesses excellent POD-like activity, also implying the strong ROS generation ability of the ZIF-8@PDA@Pt–H₂O₂ system.

To further verify the ability of ZIF-8@PDA@Pt to catalyze the production of different free radicals from H₂O₂, terephthalic acid (TA), 1,3-diphenylisobenzofuran (DPBF), and 9,10-anthracenediyl-bis(methylene)-dimalonic acid (ABDA) were chose as the indicators for the sensing of hydroxyl radical (•OH), O₂ ^•− (superoxide anion), and singlet oxygen (¹O₂), respectively. TA is a non-fluorescent molecule that can be oxidized by •OH to generated blue fluorescence. DPBF is a fluorescent molecule which possesses a specific reactivity toward ¹O₂ and O₂ ^•−, forming an endoperoxide that can decompose to give 1,2-dibenzoylbenzene. This decomposition of DPBF by ¹O₂ and O₂ ^•− can be measured by the decrease in the absorbance intensity of DPBF at 412 nm. ABDA is a highly selective probe for singlet oxygen ¹O₂, which can be oxidized with the decrease in the absorbance intensity. As shown in Figure 3, in the solution with the probes and H₂O₂, the presence of ZIF-8@PDA@P can induce significant sensing signals of •OH, O₂ ^•−, and ¹O₂. These results strongly demonstrated that ZIF-8@PDA@Pt can catalyze the production of different free radical species from H₂O₂, which is very important for bacterial disinfection.

As illustrated in the UV-vis spectra of Figure 1F, ZIF-8@PDA@Pt presents broad and intense adsorption from the ultraviolet to NIR region, manifesting ZIF-8@PDA@Pt possesses considerable photothermal conversion potential. So as to validate the supposition, the photothermal property of ZIF-8@PDA@Pt was primarily investigated, where the aqueous dispersions of ZIF-8@PDA@Pt with different concentrations were irradiated under an 808-nm NIR laser. Simultaneously, the real-time temperatures were recorded by a thermal imaging camera. It can be observed from Figures 4A–C that the temperature of the aqueous solution lifted promptly with the augment of the concentration of ZIF-8@PDA@Pt and the prolongation of irradiation time. Indeed, the constant arising trend of the curve implied that ZIF-8@PDA@Pt exhibits supreme photostability under the irradiation of the NIR laser. It can also be visually discovered from the quantitative data that the temperature of the ZIF-8@PDA@Pt solution (120 μg mL⁻¹) elevated rapidly from 28.5°C to 61.5°C within 5 min of irradiation, while the temperature of water only raised by 0.8°C under the same conditions. Such a result elucidated ZIF-8@PDA@Pt can serve as a remarkable photothermal agent. Hence, we further calculated the photothermal conversion efficiency of ZIF-8@PDA@Pt in line with a method reported previously (Supplementary Figure S2), where it can be up to 65.4% to our surprise, and this excellent property just met the experimental results we obtained as well, where the real-time temperature of the NIR-irradiated ZIF-8@PDA@Pt aqueous solution can reach up to 61.5°C in a short time.

In addition, it was found that ZIF-8@PDA@Pt presented a laser power-dependent behavior. As shown in Figure 4D, the temperature of solutions at the same time nodes increased gradually along with the increase in laser power, denoting the laser power to be imperative to the photothermal conversion ability of ZIF-8@PDA@Pt. Afterward, the thermal stability of ZIF-8@PDA@Pt was estimated by photothermal performance cycle monitoring within four laser cycles. It can be noted from Supplementary Figure S3 that there were no unmistakable temperature fluctuations in the four photothermal cycles, demonstrating ZIF-8@PDA@Pt endows considerable photothermal stability. All above results certified that ZIF-8@PDA@Pt possessed excellent photothermal properties, which can support its application for sterilization.

Inspired by the superior enzymatic activity and photothermal property of ZIF-8@PDA@Pt, the in vitro synergistic antibacterial effect of ZIF-8@PDA@Pt against Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus) was assessed by the plate counting method. As shown in Figure 5, H₂O₂ (2 mM) alone cannot induce significant influence on the bacterial viability. However, in the presence of ZIF-8@PDA@Pt, the viabilities of both E. coli and S. aureus decreased to below 40%. The ROS generated form H₂O₂ under the catalysis of ZIF-8@PDA@Pt would be responsible for this sharp decrease in the bacterial viability. Moreover, as expected, NIR irradiation greatly promoted the antibacterial efficiency of the ZIF-8@PDA@Pt/H₂O₂ system, in which the bacterial viabilities decreased to below 3%. The viability of the treated bacteria was also investigated by a live/dead staining kit, which contains two dyes, SYTO 9 and propidium iodide (PI). SYTO 9 is a membrane-permeable dye that can give a green fluorescence to indicate the live cells due to the binding with bacterial nucleic acid. PI is also a nucleic acid-binding dye used to give a red fluorescence, which can only penetrate the damaged membrane of dead bacteria. As shown in Figure 6, upon treating with ZIF-8@PDA@Pt and H₂O₂, significant amount of dead bacteria was found in the fluorescence images, and almost all of the bacteria were killed when the ZIF-8@PDA@Pt/H₂O₂ system was irradiated with the NIR light. This phenomenon was the same as that found in the plate counting experiments. These results clearly demonstrated the high synergistic antimicrobial activity of the nanozyme ZIF-8@PDA@Pt in the presence of H₂O₂ and NIR light irradiation. Notably, the nanozyme also has good biocompatibility; in the MTT assay, over 90% of the HSF cells remain alive when in the incubation with 250 μg mL⁻¹ of ZIF-8@PDA@Pt.