Release of ions enhanced the antibacterial performance of laser-generated, uncoated Ag nanoparticles.

Identifying the antibacterial mechanisms of elemental silver at the nanoscale remains a significant challenge due to the intertwining behaviors between the particles and their released ions. The open question is which of the above factor dominate the antibacterial behaviors when silver nanoparticles (Ag NPs) with different sizes. Considering the high reactivity of Ag NPs, prior research has primarily concentrated on coated particles, which inevitably hinder the release of Ag+ ions due to additional chemical agents. In this study, we synthesized various Ag NPs, both coated and uncoated, using the laser ablation in liquids (LAL) technique. By analyzing both the changes in particle size and Ag+ ions release, the impacts of various Ag NPs on the cellular activity and morphological changes of gram-negative (E. coil) and gram-positive (S. aureus) bacteria were evaluated. Our findings revealed that for uncoated Ag NPs, smaller particles exhibited greater ions release efficiency and enhanced antibacterial efficacy. Specifically, particles approximately 1.5 nm in size released up to 55 % of their Ag+ ions within 4 h, significantly inhibiting bacterial growth. Additionally, larger particles tended to aggregate on the bacterial cell membrane surface, whereas smaller particles were more likely to be internalized by the bacteria. Notably, treatment with smaller Ag NPs led to more pronounced bacterial morphological changes and elevated levels of intracellular reactive oxygen species (ROS). We proposed that the bactericidal activity of Ag NPs stems from the synergistic effect between particle-cell interaction and the ionic silver, which is dependent on the crucial parameter of particle size.

Environmental Effects of Surfactant-Free Silver Nanoparticles on Enzyme Activities, Bacterial Diversity, and Soil Function.

The effects of silver nanoparticles (Ag NPs) on the soil environment have attracted considerable research attention. Previous studies mainly focused on agent-coated Ag NPs, which inevitably introduce additional disturbance of chemical agents to the intrinsic property of Ag NPs. We investigated the environmental effects induced by pure surfactant-free Ag NPs (SF-Ag NPs), including soil enzyme activities (urease, sucrase, phosphatase, and ß-glucosidase), bacterial community structure, and functional profile, over different exposure periods in the present study. The results indicated that these enzymes, especially urease and phosphatases, exhibit different responses to SF-Ag NPs and are more susceptible to SF-Ag NPs than other enzymes. Surfactant-free Ag NPs can also induce a decrease in bacterial diversity and a change of bacterial community structure. The abundance of SF-Ag NPs in Proteobacteria increased, but decreased in Acidobacteria after 14 days of exposure. Moreover, the abundance of genus Cupriavidus was significantly higher than those of the respective controls. By contrast, SF-Ag NP exposure for 30 days could attenuate these negative effects. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) prediction revealed that SF-Ag NPs exert a negligible effect on bacterial function, thereby suggesting that functional redundancy is conduced to bacterial community tolerance to SF-Ag NPs. These findings will help us further understand the environmental toxicity of Ag NPs. Environ Toxicol Chem 2023;42:1685-1695. © 2023 SETAC.

Surface-Plasmon-Mediated Alloying for Monodisperse Au-Ag Alloy Nanoparticles in Liquid.

Plasmonic noble-metal nanoparticles with broadly tunable optical properties and catalytically active surfaces offer a unique opportunity for photochemistry. Resonant optical excitation of surface-plasmon generates high-energy hot carriers, which can participate in photochemical reactions. Although the surface-plasmon-driven catalysis on molecules has been extensively studied, surface-plasmon-mediated synthesis of bimetallic nanomaterials is less reported. Herein, we perform a detailed investigation on the formation mechanism and colloidal stability of monodisperse Au-Ag alloy nanoparticles synthesized through irradiating the intermixture of Au nanochains and AgNO3 solution with a nanosecond pulsed laser. It is revealed that the Ag atoms can be extracted from AgNO3 solution by surface-plasmon-generated hot electrons and alloy with Au atoms. Particularly, the obtained Au-Ag alloy nanoparticles without any surfactants or ligands exhibit superior stability that is confirmed by experiments as well as DLVO-based theoretical simulation. Our work would provide novel insights into the synthesis of potentially useful bimetallic nanoparticles via surface-plasmon-medicated alloying.

Hierarchical WO3-x Ultrabroadband Absorbers and Photothermal Converters Grown from Femtosecond Laser-Induced Periodic Surface Structures.

Oxygen-vacancy-rich WO3-x absorbers are gaining increasing attention because of their extensive absorbance-based applications in near-infrared shielding, photocatalysis, sterilization, interfacial evaporator and electrochromic, photochromic, and photothermal fields. Thermal treatment in an oxygen-deficient atmosphere enables us to prepare WO3-x but lacks the capacity for finely manipulating the grown structures. In this work, we present that laser-induced periodic surface structure (LIPSS) obtained by femtosecond laser ablation is a good template to grow various hierarchical WO3-x ultrabroadband absorbers and photothermal converters by thermal oxidation annealing in air. Increasing annealing temperature from 600 to 1000 °C allows the manipulation of WO3-x crystal sizes from ∼70 nm to ∼4 µm, accompanied by a color transition from brown to dark blue and finally to yellow. Benefiting from annealing-induced surface cracks and phase transition into WO3-x (containing both WO3 and W18O49) at 600 °C, excellent UV-vis-NIR-MIR ultrabroadband absorbers were produced: >90% UV-NIR absorbance (0.3-2.5 µm) and 50-90% MIR absorbance (2.5-16 µm), much better than most W-based metamaterial absorbers. The higher the annealing temperature (1000 > 800 > 600 °C), the better the photothermal performances (sample temperature as the indicator) of annealed interfaces due to the increased oxidation rates and resultant thicker oxide layers (6, 150, and 507 µm), a trend which is more apparent upon the irradiation of high-density (3160 mW/cm2) and ultrabroadband (200-2500 nm) light but much less apparent for shorter-band (200-800, 420-800, 800-2500 nm, etc.) and less-intensity (1694, 1540, 1460 mW/cm2, etc.) light irradiation. This phenomenon indicates that (1) higher-performance ultrabroadband absorbers possess a higher photothermal conversion capacity; (2) thicker-WO3-x oxide layer converters are more effective in preserving photothermal heat; and (3) both the W-LIPSS and metal tungsten substrate can quickly dissipate the photothermal heat to inhibit heat accumulation in the oxide photothermal converters. It is also proved that ablation-induced high-pressure shockwaves can produce deformation layers in the subsurfaces to release annealing-induced stresses, beneficial for the formation of less-cracked non-stoichiometric WO3-x interfaces upon annealing. High-pressure shockwaves are also capable of inducing grain refinement of LIPSS, which facilitates a homogeneous growth of small non-stoichiometric metal-oxide crystals upon annealing. Our results indicate that femtosecond laser ablation is a convenient upstream template-fabrication technique compatible with the thermal oxidation annealing method to develop advanced functional oxygen-vacancy metal-oxide interfaces.

Surface morphology and payload synergistically caused an enhancement of the longitudinal relaxivity of a Mn3O4/PtOx nanocomposite for magnetic resonance tumor imaging.

The construction of surface structures of manganese oxide nanoparticles (MONs) in order to promote their longitudinal relaxivity r1 to surpass those of commercially available Gd(iii) complexes is still a significant challenge. Herein, we successfully obtained Mn3O4/PtOx nanocomposites (NCs) with an r1 of 20.48 mM-1 s-1, four times higher than that of commercially available Gd-DTPA (5.11 mM-1 s-1). The r2/r1 ratio of these NCs is 1.46 lower than that of Gd-DTPA (2.38). This is the first time that such excellent T1 contrast performance has been achieved using MONs via synergistically utilizing the surface morphology and surface payload. These NCs are composed of porous Mn3O4"skeleton" nanostructures decorated with tiny PtOx nanoparticles (NPs) that are realized using laser ablation and irradiation in liquid and ion etching steps. Experimental results showed that the enlarged specific area of the porous Mn3O4/PtOx NCs and the payload of ultrafine PtOx NPs synergistically facilitated the T1 contrast capabilities. The former favors sufficient proton-electron interactions and the latter reduces the global molecular tumbling motion. These NCs also exhibit an evident computed tomography (CT) attenuation value of 24.13 HU L g-1, which is much better than that achieved using the commercial product iopromide (15.9 HU L g-1). The outstanding magnetic resonance (MR) imaging and CT imaging performances of the Mn3O4/PtOx NCs were proved through in vivo experiments. Histological examinations and blood circulation assays confirmed the good biosafety of the NCs. These novel findings showcase a brand-new strategy for fabricating excellent MON T1 contrast agents (CAs) on the basis of the surface structure and they pave the way for their practical clinical applications in dual-modal imaging.

Laser ablation in liquids for the assembly of Se@Au chain-oligomers with long-term stability for photothermal inhibition of tumor cells.

For the potential use of Au nanoparticles (NPs) in photothermal therapy, it is important and effective to achieve the uniaxial assembly of Au NPs to allow enhanced absorption in the near infrared (NIR) region. Herein, we first presented the construction of amorphous selenium encapsulated gold (Se@Au) chain-oligomers by successive laser ablation of Au and Se targets in sodium chloride solution without other toxic precursors, stabilizers, or templating molecules. Se@Au chain-oligomers showed evidently enhanced NIR absorption and excellent photothermal transduction efficiency (η), which was higher than 47% at 808 nm. After being stored for 1 year, the Se@Au colloids still exhibited outstanding photothermal performance. The cytotoxicity assay demonstrated that there is negligible toxicity of Se@Au chain-oligomers in cells, but cell viability declined to only 1% in phototherapeutic experiments that were implemented in vitro. In intracellular Reactive Oxygen Species (ROS) generation measurements, Se@Au chain-oligomers could trigger a 35.9% increment of ROS upon laser irradiation. The possible synergetic effects between the anticancer function of Se and photothermal behaviors of Se@Au oligomers were intended to increase ROS level in cells. Therefore, such designed Se@Au chain-oligomers of high stability exhibit promising potential for their use as in vivo photothermal therapeutic agents.

Ameliorative effects of nano-selenium against NiSO4-induced apoptosis in rat testes.

Nickel (Ni) is a common environmental pollutant, which has toxic effects on reproductive system. Nowadays, nano-selenium (Nano-Se) has aroused great attention due to its unique antioxidant effect, excellent biological activities and low toxicity. The aim of this study was to explore the protective effects of Nano-Se on NiSO4-induced testicular injury and apoptosis in rat testes. Nickel sulfate (NiSO4) (5 mg/kg b.w.) was administered intraperitoneally and Nano-Se (0.5, 1, and 2 mg Se/kg b.w., respectively) was given by oral gavage in male Sprague-Dawley rats. Histological changes in the testes were determined by H&E staining. The terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and immunohistochemistry were performed to evaluate the apoptosis in testes. Expression levels of mitochondrial apoptosis-related genes and proteins were analyzed by RT-qPCR and Western blot. The results showed that Nano-Se improved lesions of testicular tissue induced by NiSO4. Nano-Se significantly alleviated NiSO4-induced apoptosis in rat testes, as well as significantly downregulated the Bak, cytochrome c, caspase-9 and caspase-3 and upregulated Bcl-2 expression levels, all of which were involved in mitochondria-mediated apoptosis. Altogether, we concluded that Nano-Se may potentially exert protective effects on NiSO4-induced testicular injury and attenuate apoptosis, at least partly, via regulating mitochondrial apoptosis pathways in rat testes.

Nano-selenium attenuates nickel-induced testosterone synthesis disturbance through inhibition of MAPK pathways in Sprague-Dawley rats.

The aim of this study was to investigate the protective effects of Nano-Se against Ni-induced testosterone synthesis disorder in rats and determine the underlying protective mechanism. Sprague-Dawley rats were co-treated with Ni (5.0 mg/kg, i.p.) and Nano-Se (0.5, 1.0, and 2.0 mg/kg, oral gavage) for 14 days after which various endpoints were evaluated. The Ni-induced abnormal pathological changes and elevated 8-OHdG levels in the testes were attenuated by Nano-Se administration. Importantly, decreased serum testosterone levels in the Ni-treated rats were significantly restored by Nano-Se treatment, particularly at 1.0 and 2.0 mg/kg. Furthermore, the mRNA and protein levels of testosterone synthetase were increased by Nano-Se compared to the Ni group, whereas phosphorylated protein expression levels of mitogen-activated protein kinase (MAPK) pathways were suppressed by Nano-Se administration in the Ni-treated rats. Overall, the results suggest that Nano-Se may ameliorate the Ni-induced testosterone synthesis disturbance via the inhibition of ERK1/2, p38, and JNK MAPK pathways.

Paramagnetic CuS hollow nanoflowers for T2-FLAIR magnetic resonance imaging-guided thermochemotherapy of cancer.

The development of nanoplatforms with integrated therapeutic and imaging functions is necessary for highly efficient cancer therapy. Herein, 3D CuS hollow nanoflowers (HNs) consisting of 2D nanoplates are successfully fabricated through the technique of laser ablation in liquids followed by ion-exchange reactions and applied for the first time as a theranostic nanoagent for magnetic resonance imaging (MRI), photothermal therapy (PTT), and chemotherapy simultaneously. Due to the sufficient and immediate contact between the exposed cupric centers of nanoplates and protons from water molecules, CuS HNs are demonstrated to be capable of being a T1 positive contrast agent for efficient MRI of tumors on the T2-weighted fluid-attenuated inversion recovery imaging (T2-FLAIR) sequence. Besides, the hollow structure makes CuS HNs an efficient nanoplatform for drug loading with a laser-triggered drug release. Moreover, CuS HNs exhibit high photothermal conversion efficiency (30%) and good biocompatibility. The combination of PTT and chemotherapy with CuS HNs provides a significant synergistic therapeutic effect, resulting in a higher tumor inhibition ratio than PTT or chemotherapy alone. This study demonstrates a single-component multifunctional theranostic nanoagent for T2-FLAIR MRI guided thermochemotherapy, which has great potential application in theranostics of cancer.

Pure Ni nanocrystallines anchored on rGO present ultrahigh electrocatalytic activity and stability in methanol oxidation.

Pure Ni nanoparticles with ultrafine size (2.3 ± 0.4 nm) embedded on rGO present ultrahigh catalytic activity (1600 mA mg-1), excellent stability (1020 mA mg-1 retained after 1000 cycles), and a saturation concentration (4 M) of methanol for methanol oxidation reactions, which is better than that of all previously reported Ni-based catalysts.

Highly dispersed Au nanoparticles decorated WO3 nanoplatelets: Laser-assisted synthesis and superior performance for detecting ethanol vapor.

Loading of noble metal nanoparticles (NPs) on the surfaces of semiconductor oxides to form a hybrid nanostructure is an effective strategy to improve gas-sensing performance. In this study, WO3 nanoplatelets decorated with Au NPs were prepared by laser ablation in liquids (LAL) with subsequent aging and annealing treatments. Results indicated that Au NPs with an average size of 7.8 ±â€¯2.5 nm were highly dispersed on the surface of WO3 nanoplatelets. As gas-sensing materials, the obtained Au-decorated WO3 nanoplatelets showed lower operating temperature of 320 °C and higher response value of 3.5-fold in detecting ethanol molecules compared with pure WO3 nanoplatelets. Moreover, Au-decorated WO3 nanoplatelets displayed good selectivity toward ethanol compared with other tested vapors and excellent stability within several cycled measurements. These results can be ascribed to the supported Au NPs, which promote the adsorption and dissociation of oxygen species, eventually resulting in accelerated electron depletion on the surface of Au-WO3 hybrids.

Laser-Irradiation-Induced Melting and Reduction Reaction for the Formation of Pt-Based Bimetallic Alloy Particles in Liquids.

Laser melting in liquids (LML) is one of the most effective methods to prepare bimetallic alloys; however, despite being an ongoing focus of research, the process involved in the formation of such species remains ambiguous. In this paper, we prepared two types of Pt-based bimetallic alloys by LML, including Pt-Au alloys and Pt-iron group metal (iM=Fe/Co/Ni) alloys, and investigated the corresponding mechanisms of alloying process. Detailed component and structural characterizations indicate that laser irradiation induced a quite rapid formation process (not exceeding 10 s) of Pt-Au alloy nanospheres, and the crystalline structures of Pt-Au alloys is determined by the monometallic constituents with higher content. For Pt-iM alloys, we provide direct evidence to support the conclusion that FeOx /CoOx /NiOx colloids can be reduced to elementary Fe/Co/Ni particles by ethanol molecules during laser irradiation, which then react with Pt colloids to form Pt-iM sub-microspheres. These results demonstrate that LML provides an optional route to prepare Pt-based bimetallic alloy particles with tunable size, components, and crystalline phase, which should have promising applications in biological and catalysis studies.

Laser irradiation-induced Au-ZnO nanospheres with enhanced sensitivity and stability for ethanol sensing.

Incorporating noble metal nanoparticles on the surface or the inner side of semiconductors to form a hybrid nanostructure is an effective route for improving the gas sensing performance of the semiconductors. In this study, we present novel Au-decorated ZnO nanospheres (Au-ZnO NSs) obtained by the laser irradiation of liquids. Structural characterization indicated that the Au-ZnO NSs consisted of single crystalline ZnO NSs with a few Au nanoparticles decorated on their surfaces and abundant encapsulated Au nanoparticles with relatively small sizes. Laser irradiation-induced heating-melting-evaporating processes are responsible for the formation of unique Au-ZnO NSs. The gas sensing properties of the Au-ZnO NSs, as gas sensing materials, were investigated and compared with those of pure ZnO NSs. The former showed a lower working temperature, higher sensitivity, better selectivity, and good reproducibility. The response values of the Au-ZnO NS and pure ZnO NS sensors to ethanol of 100 ppm were 252 and 75 at a working temperature of 320 °C and 360 °C, respectively. Significant enhancements in gas sensing performance should be attributed to the electronic sensitization induced by the depleted layers between the encapsulated Au nanoparticles and ZnO and chemical sensitization originating from the catalytic effects of Au nanoparticles decorated on the surfaces that dissociated molecular oxygen.

Coexistence of resistance switching and negative differential resistance in the α-Fe2O3 nanorod film.

We report the coexistence of resistance switching (RS) behavior and the negative differential resistance (NDR) phenomenon in the α-Fe2O3 nanorod film grown in situ on a fluorine-doped tin oxide glass substrate. The reversible switching of the low- and high-resistance states (LRS and HRS, respectively) of the film device can be excited simply by applying bias voltage. The switching from the HRS to the LRS was initiated in the negative bias region, whereas the NDR process followed by the reversion of the HRS occurred in the positive bias region. With the increase in compliant current (CC), the carrier conduction models of the LRS and the HRS both changed and the current-voltage (I-V) relationships in the NDR region were seriously affected by the thermal process according to the level of applied CC. The co-existence of RS and NDR was possibly caused by defects during migration, such as oxygen vacancies and interstitial iron ions, which were formed in the α-Fe2O3 nanorod film. This work provided information on the ongoing effort toward developing novel electrical features of advanced transition metal oxide devices.

Highly Dispersed Ultrafine Pt Nanoparticles on Reduced Graphene Oxide Nanosheets: In Situ Sacrificial Template Synthesis and Superior Electrocatalytic Performance for Methanol Oxidation.

We report a simple and environmentally friendly route to prepare platinum/reduced graphene oxide (Pt/rGO) nanocomposites (NCs) with highly reactive MnOx colloids as reducing agents and sacrificial templates. The colloids are obtained by laser ablation of a metallic Mn target in graphene oxide (GO)-containing solution. Structural and morphological investigations of the as-prepared NCs revealed that ultrafine Pt nanoparticles (NPs) with an average size of 1.8 (±0.6) nm are uniformly dispersed on the surfaces of rGO nanosheets. Compared with commercial Pt/C catalysts, Pt/rGO NCs with highly electrochemically active surface areas show remarkably improved catalytic activity and durability toward methanol oxidation. All of these superior characteristics can be attributed to the small particle size and uniform distribution of the Pt NPs, as well as the excellent electrical conductivity and stability of the rGO catalyst support. These findings suggest that Pt/rGO electrocatalysts are promising candidate materials for practical use in fuel cells.

In situ growth of lamellar ZnTiO3 nanosheets on TiO2 tubular array with enhanced photocatalytic activity.

We report a self-sacrificed in situ growth design toward preparation of ZnTiO3-TiO2 heterojunction structure. Highly reactive zinc oxide colloidal particles derived by laser ablation in liquids can react with TiO2 nanotubes to form a lamellar ZnTiO3 nanosheet structure in a hydrothermal-treatment process. Such hybrid structural product was characterized by X-ray diffraction, scanning and transmission electron microscopy, UV-vis diffuse reflection spectroscopy and X-ray photoelectron spectroscopy. The enhanced photocatalytic activity of the hybrid structure toward degradation of methyl orange (MO) and pentachlorophenol (PCP) molecules was demonstrated and compared with single phase TiO2, as a result of the efficient separation of light excited electrons and holes at the hetero-interfaces in the two semiconductors.