Skip to main content
NCBI home page
Journal of Advanced Research logoLink to Journal of Advanced Research
. 2022 Apr 6;44:81–90. doi: 10.1016/j.jare.2022.03.015

Selective laser welding in liquid: A strategy for preparation of high-antibacterial activity nanozyme against Staphylococcus aureus

Yang Li a, Shuhan Li a, Ran Zhou a, Guqiang Li b, Xiangyou Li a,⁎
PMCID: PMC9936409  PMID: 36725195

Graphical abstract

graphic file with name ga1.jpg

Open in a new tab

Keywords: Selective laser welding in liquid, Nanozyme, Antibacterial activity, Visible light illumination

Highlights

  • •

    A facile approach of selective laser welding in liquid was proposed to prepare high-antibacterial activity nanozyme.

  • •

    Taking Ag/CeO2 nanocomposite as an example, this nanozyme can be effectively prepared under the proper laser fluence.  82.4 % sterilization rate can be obtained, which was 2.93 and 2.99 times than those of pure Ag and pure CeO2, respectively.

  • •

    This work provided a facile strategy for preparation of high-antibacterial activity nanozyme against Staphylococcus aureus.

Abstract

Nanozyme was considered as one of the most promising substitutes for antibiotics, due to the selective catalysis for pathogens. In this work, a high-antibacterial activity SOD-like nanozyme based on hybrid Ag/CeO2 nanocomposite was facilely prepared by using an innovative approach of selective laser welding in liquid. This prepared nanozyme displayed a high antimicrobial effect against Staphylococcus aureus under visible light illumination, the sterilization rate as high as 82.4%, which was 2.93 and 2.99 times higher than those of pure Ag and pure CeO2, respectively. The enhanced antibacterial activity was attributed to the anchoring of Ag nanospheres on the surface of CeO2 nanosheets, which induced the reduction of CeO2 bandgap and boosted the visible light harvesting. Therefore, the charge carriers can be effectively stimulated to produce abundant reactive oxygen species on the Ag/CeO2 nanocomposite via a SOD-like route. This work demonstrated a facile strategy for the preparation of high-antibacterial activity nanozyme, giving it great potential for scalable application in the biomedical and pharmaceutical industry.

Introduction

As a typical Gram-positive pathogen, Staphylococcus aureus (S. aureus) possessed strong metabolic versatility and pharmacy resistance, which was well adapted in humans and animals. Generally, S. aureus was existed as a member of normal microbiota and did not cause infections on the body's immune system. However, once invading the bloodstream and internal tissues, a variety of serious infections and diseases can be caused, such as pneumonia, endocarditis, diarrhea, skin and soft tissue infections (SSTIs) [1], [2]. In the past decades, antibiotic drugs were frequently used for their treatments, and a better therapeutic effect can be obtained in the early period. At present, due to the long-term abuse of these commercial antibiotics (such as methicillin, vancomycin and daptomycin), the bacterial outer membranes have been self-adapted and possess powerful drug resistance [3], [4]. In particular, the methicillin-resistant S. aureus (MRSA) was one of the major risk pathogens and posed a serious threat to human health [5], [6]. According to the latest report of the World Health Organization (WHO) in 2021 [7], the mortality rate of patients infected with MRSA was 64% higher than those of people with drug-sensitive infections. Therefore, developing a substitute for these conventional antibacterial agents was eagerly required.

Recent advances in nanomedicine research have shown the possibility of using nanoparticles to treat intractable diseases caused by bacterial infections because some distinctive characteristics of enzyme-like were found from nanomaterials and can be utilized for selectively catalytic removal of pathogens, which was also called “nanozyme” [8], [9]. For instance, cerium oxide (CeO2) nanoparticles possessed multiple enzyme-like catalytic properties based on their valance conversion between Ce4+ and Ce3+ ions [10], [11]. The rich oxygen vacancies on their surface gave it great potential to produce superoxide dismutase (SOD) and catalase (CAT) mimetic activities. These antioxidant enzyme activities were conductive to scavenge excessive reactive oxygen species for promoting wound healing and reducing inflammation induced by bacterial infection [12], [13]. However, as an n-type semiconductor, the enzyme-like activity of CeO2 was also affected by the ultrafast recombination of electron-hole pairs in the energy band. In previous reports, light stimulation was utilized to optimize the enzyme-like activity because these charge carriers can be triggered under the proper wavelength of light [14], [15]. The bandgap of CeO2 was about 2.9–3.2 eV [16], [17], which was only sensitive to ultraviolet light and the visible light response was weak (λ < 420 nm). Nevertheless, many antibacterial applications in biomedicine, such as photodynamic therapy (PDT) and photocatalytic therapy (PCT) must be driven by visible light [13], because the therapeutic system can be damaged by ultraviolet light with powerful energy, such as biological tissues and healthy cells. Hence, to solve the requirement of practical application, the bandgap of CeO2 should be modified to enhance the sensitivity for visible light. For this purpose, a hypothesis was worth considering, assuming that a special load with strong visible light absorption was inserted on the surface of CeO2, would their antibacterial activity be enhanced?

In this work, a strategy of constructing the hybrid noble metal and semiconductor nanocomposite as nanozyme for boosting antibacterial activity was proposed, because noble metal was of abundant electrons and displayed stronger visible light absorption via surface plasmon resonance (SPR) [18], [19]. Herein, the specific works of this paper were presented as follows: (i) Taking Ag nanoparticles as the load to prepare Ag/CeO2 nanocomposite. Because Ag nanoparticles were less expensive among the noble metals and possessed a powerful SPR effect. (ii) An innovative approach of selective laser welding in liquid (SLWL) was proposed to prepare the hybrid Ag/CeO2 nanocomposite. In particular, different from the conventional chemical routes (such as hydrothermal and sol-gel) [20], [21], [22], [23], SLWL was facile and environment friendly. The properties of prepared products were characterized by a variety of technologies, such as STEM, EDS, XPS, XRD and UV–Vis. (iii) The antibacterial activity of the prepared nanocomposite was evaluated by inactivation against S. aureus under visible light illumination. (iv) The possible enhanced mechanism and enzyme-like activity of Ag/CeO2 nanocomposite were proposed according to relevant XPS, UV–Vis and EPR measurements. This work demonstrated a facile approach for the preparation of high-antibacterial activity nanozyme.

Materials and methods

Materials

The Ag nanoparticles were purchased from Sigma-Aldrich (size: 100 nm, purity: 99.5%). The CeO2 nanomaterials and 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) were supplied by Macklin Biochemical Company (Shanghai, China). The ethanol solvent for materials dispersion and laser-heated quenching was obtained from the Sinopharm Chemical Reagent of China. The 0th generation freeze-dried powder of S. aureus (CMCC (B) 26003) was purchased from Wanjia Shouhua Biological Company (Beijing, China).

Synthesis of Ag/CeO2 nanocomposites

The Ag/CeO2 nanocomposite was synthesized by SLWL. The principle of SLWL was based on the different optical absorption between Ag nanoparticles, CeO2 nanomaterials and the ethanol solvent (see Fig. S1 in the ESI). Ag was much higher than ethanol solvent among the ultraviolet–visible region, CeO2 was lower than Ag, ethanol solvent was the weakest. Therefore, for the mixture of Ag nanoparticles and CeO2 nanomaterials irradiated by a 532 nm laser beam in ethanol solvent, the Ag nanoparticles would be selectively heated and quenched by ethanol solvent, while the laser effect on CeO2 nanomaterials was weak and even ignored due to this laser wavelength was restricted by its wide bandgap. After laser irradiation, the colloidal suspension of the Ag/CeO2 mixture was transformed (see the inset of Fig. S1 in ESI), confirming the laser effect was effective. Herein, the specific procedures were performed as follows:

(i) Sample preparation. The mixture of 5 mg Ag and 5 mg CeO2 was dispersed into 20 mL ethanol solvent, which was contained by a glass cell to form a colloidal suspension and homogenously dispersed under an ultrasonic oscillator for 30 min. (ii) Laser irradiation. The well-dispersed colloidal suspension was placed on a magnetic stirrer, and a magnetic rotor was added to it to prevent the colloidal particles from gravitational settling. A pulsed laser beam (Quantel brilliant b, pulse width: 8 ns, repetition rate: 10 Hz, beam diameter: 8 mm, average energy: 300 mJ, beam profiled: flattened Gaussian) with the second harmonic output wavelength of 532 nm was utilized to unfocused irradiated the suspension for 15 min. (iii) Products separation. After laser irradiation, the prepared product was separated by centrifugation and evaporation of ethanol solvent.

Characterization

The morphological properties of the prepared products were characterized by Scanning Transmission Electron Microscopy (STEM, Talos F200X) under the accelerating voltage of 200 kV. The elemental components were detected by Energy-dispersive X-ray Spectroscopy (EDS). The elemental valence states were investigated by X-ray Photoelectron Spectroscopy (XPS, AXIS-ULTRA). The phase structure was checked by X-ray Diffraction (XRD, PANalytical). The optical properties were measured by Ultraviolet–visible Spectrometer (UV–Vis, SolidSpec-3700) and Fluorescence Spectrometer (JASCO, FP-6500). The relevant reactive radicals that existed in the photocatalytic experiment were detected by using the Electron Paramagnetic Resonance (EPR, EMXnano). During the characterization, a droplet of colloidal suspension containing the prepared product was dropped on a copper net (200 mesh), and dried under an oven for STEM and EDS analysis. Similarly, a droplet colloidal suspension was dropped on a small silicon wafer and dried for XPS measurement. The powder of products for XRD measurements in the 2θ range (20–90°) was performed by Cu Kα radiation (λ = 0.15405 nm), and the standard JCPDS files were used to compare the pattern of crystalline phases. The colloidal suspension was added into a quartz cell (Hellma, 100 mm) using a pipette for UV–Vis and photoluminescence (PL) measurements. For EPR measurement, the colloidal suspension was irradiated by a Xe lamp and filtered immediately, the obtaining supernatant was added into DMPO for radicals trapping and tested under the equipment.

Bacterial cell preparation

The S. aureus was utilized as the model microorganism for photocatalytic antibacterial experiments. For obtaining these bacterial cells, the 0th generation freeze-dried powder of S. aureus was revived and cultivated in a liquid bacterial broth (LBB) under 37 ℃ and the aerophilic environment for 12 h. In particular, the cells of S. aureus in all experiments were grown in the mid-exponential phase, which was confirmed by measuring the optical density value at 600 nm (OD600) using a bio-photometer (Eppendorf, Germany) [24], [25]. After that, the bacterial suspension was diluted to obtain cell samples containing around 1 × 105 colony forming units (CFU/mL). The bacterial cell images of the as-prepared S. aureus under the Confocal Raman Microscope (CRM, Lab RAM HR800) were presented (see Fig. S2 in the ESI).

Photocatalytic antibacterial experiment

The antibacterial activity of the as-prepared Ag/CeO2 nanocomposites was investigated toward the inactivation of S. aureus. For comparison, the same amount of pure Ag (including Raw Ag and Lasered Ag), pure CeO2 (Raw CeO2 and Lasered CeO2), and the raw Ag/CeO2 mixture were also investigated. During the experiment, 10 μg photocatalytic antibacterial agents, such as pure Ag, pure CeO2, raw Ag/CeO2 mixture and as-prepared Ag/CeO2 nanocomposite were added into 1 mL LBB contained around 1 × 105 CFU/mL of S. aureus, respectively. Then, irradiating them under a LED visible light (wavelength: λ > 420 nm, power: 150 W) for 1 h. After that, 20 μL of the irradiated bacterial suspensions were spread onto the Luria Bertani (LB) plates to grow overnight at 37℃ under the aerophilic environment. Their displayed antibacterial activities were evaluated by calculating the bacterial colony counts and compared to control plates [26], [27]. And that the bacterial colony counts on the LB plate were facilely calculated by using Image J software (See Fig. S3 in the ESI). Particularly, the control plates were set as blank cases and those of no light illumination, respectively.

Results and discussion

Morphologies

As shown in Fig. 1, the morphological images of pure Ag nanoparticles and pure CeO2 nanomaterials before and after laser irradiation in ethanol solvent were presented.

Fig. 1.

Fig. 1

Open in a new tab

STEM images of pure Ag and pure CeO2 before and after laser irradiation. (a) Raw Ag. (b) Laser Ag, the histogram inset was the distribution of average particle size. (c) Raw CeO2. (d) Laser CeO2.

For pure Ag, the nanoparticles before laser irradiation were agglomerated (Raw Ag), the initial particle size was about 100 nm. After laser irradiation, the irregular nanoparticles transformed to be nanospheres (Laser Ag), with an average particle size of 20 nm (see histogram inset). For pure CeO2, the initial size of the nanosheet was more than 100 nm (Raw CeO2). After laser irradiation, the morphological property and sheet size were hardly transformed (Laser CeO2), still maintaining the irregular nanosheets. Confirming the 532 nm laser effect on pure Ag and pure CeO2 was different. Herein, the laser fluence was about 0.597 J/(Pulse·cm2). In the previous report, using the thermodynamic “heating-melting-evaporation” (HME) model described by Takami et al. [28], Pyatenko and co-workers have numerically investigated the relationship between laser fluence of 532 nm and the particle size of Ag nanoparticles [29], which revealed that the phase of Ag nanoparticles under this sufficient density was the mixture of liquid and gas states (marked by “L + G” in reference). Therefore, the Ag nanoparticles after laser irradiation can be melted and even exploded to be fragmentation, so that the nanospheres with decreased size can be formed under liquid quenching. While the laser energy of 532 nm was resisted by the wide-bandgap of CeO2.

As shown in Fig. 2, the morphological images of the Ag and CeO2 mixture after laser irradiation in ethanol solvent were presented. Fig. 2 (a) and (b) were observed from two different horizons. (c) and (d) were their local magnifications. The nanospheres of Ag and nanosheets of CeO2 were sandwiched together. Under the high-resolution mode (HR-TEM), their composite interfaces can be observed (see inset). In Fig. 2 (c), the lattice spacing between two components was found to be 0.24 nm and 0.27 nm, corresponding to the (1 1 1) plane of Ag and (2 0 0) plane of CeO2, respectively. In Fig. 2 (d), the lattice spacing between two components was found to be 0.24 nm and 0.31 nm, which were properly matched with the (1 1 1) plane of Ag and (1 1 1) plane of CeO2, respectively. The composite interfaces can be observed, confirming the Ag/CeO2 nanocomposites were successfully prepared.

Fig. 2.

Fig. 2

Open in a new tab

The STEM images of Ag and CeO2 mixture after laser irradiation. (a) and (b) were viewed from two different horizons. (c) and (d) were their magnifications, respectively. Their insets were composite interfaces between Ag and CeO2 under HR-TEM.

EDS mapping

To investigate the elemental components in the prepared Ag/CeO2 nanocomposite, the EDS mapping was performed, as shown in Fig. 3.

Fig. 3.

Fig. 3

Open in a new tab

EDS mapping of the prepared Ag/CeO2 nanocomposite. (a) HAADF. (b) O. (c) Ce. (d) Ag. (e) mixed. (f) The Energy-dispersive spectrum of Area #1 (marked by a yellow symbol) from (e).

In Fig. 3 (a), the High-Angle Annular Dark-Field (HAADF) image from a random area of the prepared products was presented. The corresponding O, Ce and Ag elements were distributed in Fig. 3 (b)-(d), respectively. Fig. 3 (e) was their mixed distribution, which was well-matched with the HAADF area, revealing that the Ag component was sandwiched on the surface of CeO2. Moreover, the elemental distribution in a small area was also investigated (see Area #1 in Fig. 3 (e), a yellow symbol), the Energy-dispersive spectrum was presented in Fig. 3 (f). The signals of O, Ce and Ag can be observed (Cu was from the copper net), reconfirmed the laser-welded Ag/CeO2 nanocomposite was prepared.

XPS analysis

Valance states of the surface atoms in the prepared Ag/CeO2 nanocomposite were investigated by XPS measurement, as shown in Fig. 4.

Fig. 4.

Fig. 4

Open in a new tab

XPS spectrum of CeO2 before and after welding with Ag. (a) Full spectra. (b) The typical high-resolution XPS spectra of Ag 3d. (c) The typical high-resolution XPS spectra of Ce 3d. (d) The typical high-resolution XPS spectra of O 1s.

Fig. 4 (a) was the full spectra of CeO2 before and after welding with Ag. For pure CeO2, the dominant peaks for valance states of C 1s, O 1s and Ce 3d were detected. After welding with Ag, the peak of the Ag 3d state was also illustrated. As the high-resolution XPS spectra of Ag 3d in Fig. 4 (b), two peaks located at 368.4 eV and 374.4 eV with a spin energy separation of 6 eV were assigned to the binding energy of Ag 3d5/2 and Ag 3d3/2, respectively, which verified that the Ag nanoparticles deposited onto the surface of CeO2 were metallic state [30]. Fig. 4 (c) was a typical high-resolution XPS spectrum of Ce 3d, the dominant peaks at 882.3 eV, 888.8 eV, 898.4 eV, 900.9 eV, 907.6 eV, and 916.8 eV were synchronously illustrated, which were corresponding to the binding energy of v, v″, v‴, u, u″ and u‴ of Ce4+, respectively [31]. In Fig. 4 (d), the typical high-resolution XPS spectra of O 1s for CeO2 and the prepared Ag/CeO2 was presented. Thereinto, two peaks located at 529.2 eV and 532.5 eV were assigned to the binding energy of Ce-O in CeO2 lattice (marked as “OLattice”) and H-O on the surface adsorbed (marked as “OAdsorbed”), respectively [20], [24]. After welding with Ag, the surface adsorbed oxygen species was enhanced revealing that introduction of the Ag component was beneficial for the enrichment of the oxygen element.

XRD analysis

The phase structure of the prepared Ag/CeO2 nanocomposite was investigated by XRD. As shown in Fig. 5, the XRD patterns of pure Ag, pure CeO2 and the prepared Ag/CeO2 nanocomposite were presented.

Fig. 5.

Fig. 5

Open in a new tab

XRD patterns for pure Ag (a), pure CeO2 (b) and the prepared Ag/CeO2 nanocomposite (c).

In Fig. 5 (a), the dominant peaks at 38.1°, 44.3°, 64.4°, 77.4°, and 81.5° in 2θ range were observed, which were matched with the (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2) planes of face-centred-cubic metallic Ag (JCPDS, 00-004-0783) [32]. In Fig. 5 (b), the peaks at 28.6°, 33.1°, 47.6°, 56.4°, 59.2°, 69.5°, 76.8°, 79.2°, and 88.6° within 2θ were observed, which were corresponding to the (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (3 3 1), (4 2 0), (4 2 2) planes of fluorite crystal structure CeO2 (JCPDS, 03-065-5923) [33], [34]. In Fig. 5 (c), compared with characteristic peaks of pure Ag (marked by green symbol “&”) and pure CeO2 (marked by blue symbol “*”), they were synchronously involved in the Ag/CeO2 nanocomposite. There were no additional peaks presented, confirming the phase structures of Ag and CeO2 after laser irradiation were stable.

Antibacterial activity

As shown in Fig. 6, the antibacterial activity of the prepared Ag/CeO2 nanocomposite was evaluated by the inactivation of S. aureus. Fig. 6 (a) was the LB plates affected by different antibacterial agents, such as blank case, pure Ag, pure CeO2 and the mixture of Ag/CeO2 under laser welding or not. For comparison, these cases under visible light illumination (marked as “Light”) and no illumination (marked as “Dark”) were illustrated, respectively. Fig. 6 (b) was the corresponding histogram of bacterial colony counts under different antibacterial agents. Herein, all the bacterial colony counts were repeated calculated 3 times for accuracy. Fig. 6 (c) was the histogram of sterilization rate for different antibacterial agents under visible light illumination. In particular, the sterilization rate was described as the percent ratio of removed colony counts under light and the initial colony counts without light.

Fig. 6.

Fig. 6

Open in a new tab

The antibacterial effect for different antibacterial agents. (a) The LB plates were affected by the blank case, pure Ag, pure CeO2 and the mixture of Ag/CeO2 under laser welding or not. (b) The histogram of bacterial colony counts for different antibacterial agents. (c) The histogram of the sterilization rate for different antibacterial agents under visible-light illumination.

In Fig. 6. (a), it can be observed that the bacterial colonies affected by antibacterial agents were much less than the LB plates without antibacterial agents (blank cases), confirming that the S. aureus can be effectively removed under the degradation of these antibacterial agents. For blank case (control plate), the bacterial colony counts under visible light illumination (see “1L”, 3.2 × 107 CFU/mL) was slightly less than that without illumination (see “1D”, 3.32 × 107 CFU/mL), confirming visible light illumination was a weak effect on the pure bacterial suspension. For Ag nanoparticles, whether they were treated by laser (see “Raw Ag” and “Laser Ag”), their bacterial colony counts were much less than blank cases. Because the bacterial cells in suspension can be killed by the release of Ag+ ions. As Yin and Gu et al. described in their previous review [13], when a sufficiently high and durable Ag+ ions content was existed in bacterial suspension, the protein inactivation and structural deformation of bacterial cells can be caused, because the toxic effect and mimetic enzymes properties (such as SOD-like and CAT-like activity) they displayed. After visible light illumination, the bacterial colony counts on LB plates containing Raw Ag and Laser Ag were less than those of no illumination (see “2L”, “3L”, “2D” and “3D”), the sterilization rates were 28.1% and 32.5%, respectively. Confirming the visible light illumination was beneficial for the generation of mimetic enzyme activity of Ag nanoparticles in the antibacterial application.

For CeO2 nanosheets, whether treated by laser (see “Raw CeO2” and “Laser CeO2”), fewer bacterial colonies were displayed than blank cases. Confirming the bacterial cells also can be damaged by CeO2. It was attributed to the valance conversion between Ce3+ and Ce4+ ions in the crystal lattice, giving it a strong redox ability. As the review described by Zhai and Du et al. [10], the crystal structure of CeO2 was a face-centred-cubic fluorite type, the Ce4+ and O2− were located on their octahedral interstitial and tetrahedral interstitial sites, respectively. In the bacterial suspension, with the formation and migration of oxygen vacancies, the oxygen atom accompanied by two valence electrons were released. These electrons can be captured by Ce4+ ions and oxygen molecules in suspension so that Ce3+ ions and superoxide anion (•O2−) would be produced. With the increasing ratio of Ce3+/Ce4+, a SOD-like activity can be displayed according to this mechanism: •O2− + Ce3+ + 2H+ → H2O2 + Ce4+ [35]. Therefore, reactive oxygen species (ROS) such as •O2− and H2O2 can be generated to kill the bacterial cells via oxidative stress. However, with the ratio of Ce3+/Ce4+ decreasing, the Ce3+ ions also can be oxidized to be Ce4+ ions and displayed a CAT-like activity according to this approach: H2O2 + 2Ce3+ + 2H+ → 2H2O + 2Ce4+ [10], [36]. During this oxidization process, the hydrogen peroxides (H2O2) were scavenged, so that CeO2 can be dual served as ROS producer and scavenger, it was mainly determined by the relative content of Ce3+/Ce4+ [37]. In addition, the bacterial colonies on plates of CeO2 were also lower than those of no illumination (see “4L”, “5L”, “4D” and “5D”), the sterilization rates were 27.6% and 30.4%, respectively. Confirming the visible light illumination was also beneficial for the antibacterial activity of CeO2 nanosheets.

For the mixture of Ag/CeO2, before laser welding, the photocatalytic sterilization rate was 24.1%. After laser welding, Ag/CeO2 nanocomposite was successfully prepared, a better antibacterial activity can be obtained. The bacterial colony counts under visible light illumination was rare (see “7L”, 0.39 × 107 CFU/mL), and the sterilization rate was as high as 82.4%, which was boosted 2.93 and 2.99 times than those of pure Ag (28.1%) and pure CeO2 (27.6%), respectively. Furthermore, compared with the sterilization rates of vancomycin (35.6%) and daptomycin (29.4%) for antibacterial of S. aureus under visible light illumination (see Fig. S4 in the ESI), this Ag/CeO2 nanocomposite also displayed a superior performance, which was 2.31 and 2.8 times higher than those of commercial antibiotics, respectively.

Enhanced mechanism

The enhanced antibacterial activity of Ag/CeO2 nanocomposite was attributed to the modification of Ag nanospheres on the surface of CeO2 nanosheets, which boosted the visible light absorption and reduced the bandgap so that more charge carriers can be generated by visible light illumination, and thus abundant ROS can be produced assisted with a SOD-like activity. As shown in Fig. 7.

Fig. 7.

Fig. 7

Open in a new tab

(a) Optical properties for different antibacterial agents, including pure Ag nanoparticles, pure CeO2 nanosheets and the mixture of Ag/CeO2 irradiated by laser. (b) photoluminescence properties (PL, excited at 425 nm). (c) The shift of CeO2 bandgap. (d) Enhanced mechanism of antibacterial activity.

Fig. 7 (a) was the optical properties for different antibacterial agents. Whether treated by laser, the absorption peak of CeO2 nanosheets was located in the ultraviolet range (UV, about 300–400 nm). Its laser effect was very weak, as revealed in STEM analysis. For Ag nanoparticles, after laser irradiation, a strong resonant peak from their SPR effect was illustrated. For their mixture, Ag/CeO2 nanocomposite can be produced after selective laser welding. So that their optical absorption was enhanced and extended to the visible region according to the coupling of Ag nanospheres, the SPR effect of Ag and UV peak of CeO2 were synergetic. Therefore, the visible light can be effectively absorbed by Ag/CeO2 nanocomposite. Fig. 7 (b) was the PL properties for different antibacterial agents. The laser-welded Ag/CeO2 nanocomposite displayed the lowest intensity under the excitation of 425 nm, revealing the lowest recombination rate for charge carriers stimulated by visible light (λ > 420 nm). Fig. 7 (c) was the redshift of the bandgap for CeO2 before and modified with Ag. The bandgap of pure CeO2 nanosheets was about 2.9 eV, after welding with Ag nanospheres, the bandgap of Ag/CeO2 nanocomposite was greatly decreased due to the introduction of the SPR effect. Hence, the valence electrons of Ag nanoparticles can be transferred to the interface of two components. In addition, with the reduction of bandgap and enhanced sensitivity to visible light, more charge carriers in Ag/CeO2 nanocomposite can be excited by visible light (revealed by lowest PL intensity), which was beneficial for the generation of abundant ROS. Because the surface adsorbed oxygen species was also enhanced (see XPS in Fig. 4 (d)), which promoted the combination rate of charge carriers and oxygen content. Hence, the antibacterial activity was enhanced.

As shown in Fig. 7 (d), for pure CeO2 nanosheets, its SOD-like activity has been described. Due to the release of the oxygen atom and valence electrons in bacterial suspension, the Ce3+ ions and superoxide anions can be produced. With the ratio increasing of Ce3+/Ce4+, ROS, such as H2O2 can be generated. While in Ag/CeO2 nanocomposite, the Ag nanospheres were welded with CeO2 nanosheets, the valence electrons of Ag can be transferred to the composite crystal lattice, which can be utilized to generate more Ce3+. Not only the antibacterial effect can be displayed by the introduction of Ag+ ions (see XPS in Fig. 4 (b)), but also a SOD-like activity can be presented by increasing Ce3+ ions. Therefore, a general enhanced SOD-like activity can be displayed in Ag/CeO2 nanocomposite.

Determination of SOD-like activity

The SOD-like activity of the prepared Ag/CeO2 nanocomposite can be revealed by the determination of the superoxide radicals via photogeneration. The generated superoxide radicals can be detected by EPR measurement. During the detection, for comparison, a variety of antibacterial agents were added into the methanol solution (kermel) to form 2.5 mg/mL colloidal suspension, respectively. After then, the colloidal suspension was magnetically stirred and irradiated by a 350 W Xe lamp for 180 s. After filtering, the supernatant was added into 20 μL DMPO for trapping superoxide radicals [38]. As shown in Fig. 8, the EPR signals of DMPO trapped superoxide radials (DMPO-•O2−) were presented. For blank case, not involving any antibacterial agent, no EPR signal was observed, revealing that the pure DMPO and methanol solution without paramagnetic response. For Ag nanoparticles, whether laser-treated, their EPR signals were too weak to be detected, confirming rare superoxide radicals were generated from Ag. For CeO2 nanosheets, whether laser-treated, their EPR signals can be observed, confirming the superoxide radicals can be effectively generated from CeO2. For the mixture Ag/CeO2, a powerful EPR signal can be detected after laser welding. Compared with pure Ag and pure CeO2, confirming that abundant superoxide radicals were generated from Ag/CeO2 nanocomposite. This was agreed well with the optical properties.

Fig. 8.

Fig. 8

Open in a new tab

EPR signals of DMPO-•O2− for different antibacterial agents in methanol solution under the lamp illumination of 180 s.

Conclusions

In summary, we have demonstrated a facile approach for the preparation of Ag/CeO2 nanocomposite with high-antibacterial activity by SLWL. During the preparation, the Ag nanoparticles were transformed to be nanospheres and combined with CeO2 nanosheets under the proper laser selectively welding. The antibacterial activity of the prepared nanocomposite was evaluated by sterilization of S. aureus under visible light illumination. A high sterilization rate of 82.4% was achieved, which was 2.93 and 2.99 times those of pure Ag and pure CeO2, respectively. Confirming the anchoring of Ag nanoparticles on the surface of CeO2 nanosheets was beneficial for boosting antibacterial activity against S. aureus. The relevant nanozyme-like mechanism of Ag/CeO2 nanocomposite was discussed, in which the introduction of Ag not only boosted the Ag+ ions content, but also promoted the ratio of Ce3+/Ce4+, and thus a general enhanced SOD-like activity can be displayed. Moreover, this nanozyme-like activity was directly revealed by EPR measurement. This work demonstrated that constructing an Ag/CeO2 nanocomposite by selective laser welding in liquid was a facile approach for the preparation of high-antibacterial activity nanozyme.

Compliance with Ethics Requirements

This article does not contain any studies with human or animal subjects.

CRediT authorship contribution statement

Yang Li: Conceptualization, Investigation, Supervision. Shuhan Li: Investigation. Ran Zhou: . Guqiang Li: . Xiangyou Li: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the Department of Science and Technology of Guangdong Province in China (2020B1212060067), and the Fundamental Research Funds for the Central Universities (2021yjsCXCY063). The authors sincerely appreciate the Analytical and Testing Center of Huazhong University of Science and Technology for sample characterization and data measurements.

Footnotes

Peer review under responsibility of Cairo University.

Appendix A

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jare.2022.03.015.

Appendix A. Supplementary material

The following are the Supplementary data to this article:

Supplementary data 1
mmc1.docx (716.5KB, docx)

References

  • 1.Cong Y., Yang S., Rao X. Vancomycin resistant Staphylococcus aureus infections: A review of case updating and clinical features. J Adv Res. 2020;21:169–176. doi: 10.1016/j.jare.2019.10.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Ahmed T., Shahid M., Noman M., Nizai M.B.K., Zubair M., Almatroudi A., et al. Bioprospecting a native silver-resistant Bacillus safensis strain for green synthesis and subsequent antibacterial and anticancer activities of silver nanoparticles. J Adv Res. 2020;24:475–483. doi: 10.1016/j.jare.2020.05.011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Ye X., Huang Y., Zhou C., Liu X., Zhao W., Zhao X., et al. MSI-1 combats drug-resistant S. aureus by affecting bacterial viability and inhibiting carotenoid pigment production. Microbiol Res. 2022;255:126909. doi: 10.1016/j.micres.2021.126909. [DOI] [PubMed] [Google Scholar]
  • 4.Tian S., Hu Y., Chen X., Liu C., Xue Y., Han B. Green synthesis of silver nanoparticles using sodium alginate and tannic acid: characterization and anti-S. aureus activity. Int J Biol Macromol. 2022;195:515–522. doi: 10.1016/j.ijbiomac.2021.12.031. [DOI] [PubMed] [Google Scholar]
  • 5.Papadopoulos P., Angelidis A.S., Papadopoulos T., Kotzamanidis C., Zdragas A., Papa A., et al. Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in bulk tank milk, livestock and dairy-farm personnel in north-central and north-eastern Greece: Prevalence, characterization and genetic relatedness. Food Microbiol. 2019;84:103249. doi: 10.1016/j.fm.2019.103249. [DOI] [PubMed] [Google Scholar]
  • 6.Zeng F., Weng Z., Zheng H., Xu M., Liang X., Duan J. Preparation and characterization of active oxidized starch films containing licorice residue extracts and its potential against methicillin-resistant S. aureus. Int J Biol Macromol. 2021;187:858–866. doi: 10.1016/j.ijbiomac.2021.07.179. [DOI] [PubMed] [Google Scholar]
  • 7.https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance.
  • 8.Zhang S., Li Y., Liu C., Zhang Y., Sun P., Lan X., et al. Supramolecular amino acid-based metallo-nanozyme through multicomponent coordination self-assembly for in-site tumor synergistic catalytic-chemotherapy. Chem Eng J. 2022;437:135312. [Google Scholar]
  • 9.Su Y., Wu F., Song Q., Wu M., Mohammadniaei M., Zhang T., et al. Dual enzyme-mimic nanozyme based on single-atom construction strategy for photothermal-augmented nanocatalytic therapy in the second near-infrared biowindow. Biomaterials. 2022;281:121325. doi: 10.1016/j.biomaterials.2021.121325. [DOI] [PubMed] [Google Scholar]
  • 10.Zhang M., Zhang C., Zhai X., Luo F., Du Y., Yan C. Antibacterial mechanism and activity of cerium oxide nanoparticles. Sci China Mater. 2019;62:1727–1739. [Google Scholar]
  • 11.Xu C., Lin Y., Wang J., Wu L.i., Wei W., Ren J., et al. Nanoceria-Triggered Synergetic Drug Release Based on CeO2-Capped Mesoporous Silica Host-Guest Interactions and Switchable Enzymatic Activity and Cellular Effects of CeO2. Adv Healthc Mater. 2013;2(12):1591–1599. doi: 10.1002/adhm.201200464. [DOI] [PubMed] [Google Scholar]
  • 12.Hu M., Korschelt K., Daniel P., Landfester K., Tremel W., Bannwarth M.B. Fibrous nanozyme dressings with catalase-like activity for H2O2 reduction to promote wound healing. ACS Appl. Mater. Interfaces. 2017;9(43):38024–38031. doi: 10.1021/acsami.7b12212. [DOI] [PubMed] [Google Scholar]
  • 13.Mei L., Zhu S., Liu Y., Yin W., Gu Z., Zhao Y. An overview of the use of nanozymes in antibacterial application. Chem Eng J. 2021;418:129431. [Google Scholar]
  • 14.Zhang J., Liu J. Light-activated nanozymes: catalytic mechanisms and applications. Nanoscale. 2020;12(5):2914–2923. doi: 10.1039/c9nr10822j. [DOI] [PubMed] [Google Scholar]
  • 15.Liu Y., Wang X., Wei H. Light-responsive nanozymes for biosensing. Analyst. 2020;145(13):4388–4397. doi: 10.1039/d0an00389a. [DOI] [PubMed] [Google Scholar]
  • 16.Aslam M., Qamar M.T., Soomro M.T., Danish E.Y., Ismail I.M.I., Hameed A. The role of size-controlled CeO2 nanoparticles in enhancing the stability and photocatalytic performance of ZnO in natural sunlight exposure. Chemosphere. 2022;289:133092. doi: 10.1016/j.chemosphere.2021.133092. [DOI] [PubMed] [Google Scholar]
  • 17.Subashini A., Prasath P.V., Sagadevan S., Lett J.A., Fatimah I., Mohammad F., et al. Enhanced photocatalytic degradation efficiency of graphitic carbon nitride-loaded CeO2 nanoparticles. Chem Phys Lett. 2021;769:138441. [Google Scholar]
  • 18.Liu C., Zhang M., Geng H., Zhang P., Zheng Z., Zhou Y., et al. NIR enhanced peroxidase-like activity of Au@CeO2 hybrid nanozyme by plasmon-induced hot electrons and photothermal effect for bacteria killing. Appl Catal B-Environ. 2021;295:120317. [Google Scholar]
  • 19.Sama B., Sarma B.K. Fabrication of Ag/ZnO heterostructure and the role of surface coverage of ZnO microrods by Ag nanoparticles on the photophysical and photocatalytic properties of the metal-semiconductor system. Appl Surf Sci. 2017;410:557–565. [Google Scholar]
  • 20.Jiang G., Su Y., Li H., Chen Y., Li S., Bu Y., et al. Insight into the Ag-CeO2 interface and mechanism of catalytic oxidation of formaldehyde. Appl Surf Sci. 2021;549:149277. [Google Scholar]
  • 21.Rao R., Liang H., Hu C., Dong H., Dong X., Tang Y., et al. A melamine-assisted pyrolytic synthesis of Ag-CeO2 nanoassemblys for CO oxidation: Activation of Ag-CeO2 interfacial lattice oxygen. Appl Surf Sci. 2022;571:151283. [Google Scholar]
  • 22.Soni B., Makkar S., Biswas S. Defects induced tailored optical and magnetic properties of Zn-doped CeO2 nanoparticles synthesized by a facile sol-gel type process. J Alloy Compd. 2021;879:160149. [Google Scholar]
  • 23.Gnanam S., Rajendran V. Facile sol-gel preparation of Cd-doped cerium oxide (CeO2) nanoparticles and their photocatalytic activities. J Alloy Compd. 2018;735:1854–1862. [Google Scholar]
  • 24.Xia P., Cao S., Zhu B., Liu M., Shi M., Yu J., et al. Designing a 0D/2D S-Scheme Heterojunction over Polymeric Carbon Nitride for Visible-Light Photocatalytic Inactivation of Bacteria. Angew Chem Int Ed. 2020;59:5218–5225. doi: 10.1002/anie.201916012. [DOI] [PubMed] [Google Scholar]
  • 25.Gawade P., Gunjal G., Sharma A., Ghosh P. Reconstruction of transcriptional regulatory networks of Fis and H-NS in Escherichia coli from genome-wide data analysis. Genomics. 2020;112:1264–1272. doi: 10.1016/j.ygeno.2019.07.013. [DOI] [PubMed] [Google Scholar]
  • 26.Jaguezeski A.M., Glombowsky P., da Rosa G., Da Silva A.S. Daily intake of a homeopathic agent by dogs modulates white cell defenses and reduces bacterial counts in feces. Microb Pathogenesis. 2021;156:104936. doi: 10.1016/j.micpath.2021.104936. [DOI] [PubMed] [Google Scholar]
  • 27.Dat N.M., Thinh D.B., Huong L.M., Tinh N.T., Linh N.T.T., Hai N.D., et al. Facile synthesis and antibacterial activity of silver nanoparticles-modified graphene oxide hybrid material: the assessment, utilization, and anti-virus potentiality. Mater Today Chem. 2022;23:100738. doi: 10.1016/j.mtchem.2021.100738. [DOI] [Google Scholar]
  • 28.Takami A., Kurita H., Koda S. Laser-induced size reduction of noble metal particles. J Phys Chem B. 1999;103(8):1226–1232. [Google Scholar]
  • 29.Pyatenko A., Wang H., Koshizaki N., Tsuji T. Mechanism of pulse laser interaction with colloidal nanoparticles. Laser Photonics Rev. 2013;7(4):596–604. [Google Scholar]
  • 30.Wang K., Huang J. Natural cellulose derived nanofibrous Ag-nanoparticle/SnO2/carbon ternary composite as an anodic material for lithium-ion batteries. J Phys Chem Solids. 2019;126:155–163. [Google Scholar]
  • 31.Wang Y., Bi F., Wang Y., Jia M., Tao X., Jin Y., et al. MOF-derived CeO2 supported Ag catalysts for toluene oxidation: The effect of synthesis method. Mol Catal. 2021;515:111922. [Google Scholar]
  • 32.Naskar A., Lee S., Kim K. Easy One-Pot Low-Temperature Synthesized Ag-ZnO Nanoparticles and Their Activity Against Clinical Isolates of Methicillin-Resistant Staphylococcu saureus. Front Bioeng Biotech. 2020;8:216. doi: 10.3389/fbioe.2020.00216. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.Ma L., Seo C.Y., Chen X., Li J., Schwank J.W. Sodium-promoted Ag/CeO2 nanospheres for catalytic oxidation of formaldehyde. Chem Eng J. 2018;350:419–428. [Google Scholar]
  • 34.Bagheri S., Khalil I., Julkapli N.M. Cerium (IV) oxide nanocomposites: Catalytic properties and industrial application. J Rare Earth. 2021;39:129–139. [Google Scholar]
  • 35.Korsvik C., Patil S., Seal S., Self W.T. Superoxide dismutase mimetic properties exhibited by vacancy engineered ceria nanoparticles. Chem Commun. 2007;303:1056–1058. doi: 10.1039/b615134e. [DOI] [PubMed] [Google Scholar]
  • 36.Huang Y., Ren J., Qu X. Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications. Chem Rev. 2019;119(6):4357–4412. doi: 10.1021/acs.chemrev.8b00672. [DOI] [PubMed] [Google Scholar]
  • 37.Babu K.S., Anandkumar M., Tsai T., Kao T., Inbaraj B.S., Chen B. Cytotoxicity and antibacterial activity of gold-supported cerium oxide nanoparticles. Int J Nanomed. 2014;9:5515–5531. doi: 10.2147/IJN.S70087. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Wei Z., Gao H., Fu G., Yang G., Li J., Liu P.u. Construction of GQDs-Decorated Ultrathin Bi2WO6 Nanosheets Hydrogel: a Recyclable-Flexible Platform with Excellent Piezo-Photocatalytic Activity for High-Performance Water Decontamination and its Theoretical Interpretation. Part Part Syst Charact. 2021;38(12):2100198. [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary data 1
mmc1.docx (716.5KB, docx)

Articles from Journal of Advanced Research are provided here courtesy of Elsevier

RESOURCES