SiO2@AuAg/PDA hybrid nanospheres with photo-thermally enhanced synergistic antibacterial and catalytic activity.

Wastewater discharged from industrial, agricultural and livestock production contains a large number of harmful bacteria and organic pollutants, which usually cause serious harm to human health. Therefore, it is urgent to find a "one-stone-two-birds" strategy with good antimicrobial and pollutant degradation activity for treating waste water. In this paper, SiO2@AuAg/Polydopamine (SiO2@AuAg/PDA) core/shell nanospheres, which possessed synergistic "Ag+-release-photothermal" antibacterial and catalytic behaviors, have been successfully prepared via a simple in situ redox polymerization method. The SiO2@AuAg/PDA nanospheres showed good catalytic activity in reducing 4-nitrophenol to 4-aminophenol (0.576 min-1 mg-1). Since the AuAg nanoclusters contain both gold and silver elements, they provided a high photothermal conversion efficiency (48.1%). Under NIR irradiation (808 nm, 2.5 W-2), the catalytic kinetics were improved by 2.2 times. Besides the intrinsic Ag+-release, the photothermal behavior originating from the AuAg bimetallic nanoclusters and the PDA component of SiO2@AuAg/PDA also critically improved the antibacterial performance. Both E. coli and S. aureus could be basically killed by SiO2@AuAg/PDA nanospheres at a concentration of 90 µg mL-1 under NIR irradiation. This "Ag+-release-photothermal" coupled sterilization offers a straightforward and effective approach to antimicrobial therapy, and further exhibits high potential in nanomedicine for combating bacterial contamination in environmental treatment and biological fields.

Size-dependent magnetomechanically enhanced photothermal antibacterial effect of Fe3O4@Au/PDA nanodurian.

The global health crisis of bacterial resistance to antibiotics requires innovative antibacterial strategies. One promising solution is the exploitation of multifunctional nanoplatforms based on non-resistant antibacterial mechanisms. This work reports a novel Fe3O4@Au/polydopamine (PDA) nanodurian with excellent photothermal-magnetomechanic synergistic antibacterial effects. The one-step formed Au/PDA hybrid shell provides good photothermal properties and spiky surfaces for enhanced magnetomechanic effects. Upon near-infrared (NIR) irradiation, the Fe3O4@Au/PDA nanodurian (200 µg mL-1) achieved nearly 100% antibacterial effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The efficiency of photothermal antimicrobial activity was further enhanced by the application of a rotating magnetic field (RMF), with the sterilization efficiency being increased by up to more than a half compared to the action alone. Interestingly, the size of the nanodurian has a significant impact on the synergistic sterilization effect, with larger particles showing a superior performance due to stronger chain-like structures in the magnetic field. Finally, the Fe3O4@Au/PDA nanodurian also demonstrates effective biofilm removal, with larger particles exhibiting the best eradication effect under the photothermal-magnetomechanic treatment. Overall, this magnetic field enhanced photothermal antibacterial strategy provides a promising broad-spectrum antimicrobial solution to combat bacterial infections. Thus, it possesses great potential in future nanomedicine and pollution treatment.

A MXene@AgAu@PDA nanoplatform loaded with AgAu nanocages for enhancing catalytic activity and antibacterial performance.

With the rapid development of social industrialization, environmental problems seriously threaten people's health, especially water pollution. Therefore, there is an urgent need to construct a multifunctional nanoplatform for different scenarios. Two-dimensional MXene@AgAu@PDA nanosheets loaded with AgAu bimetallic nanocages have been prepared by a one-step method. First, the in situ generated MXene@Ag is used as an auxiliary template, and then HAuCl4 and dopamine are added for in situ redox-oxidizing polymerization reactions to obtain AgAu catalytic nanocages and the protective polydopamine (PDA) layer which can improve the stability and biocompatibility. MXene and PDA have excellent photothermal conversion ability while hollow AgAu nanocages have strong absorption in the near-infrared region and a local surface plasmonic resonance effect. In comparison to the catalytic reaction rates under dark and room temperature conditions, the catalytic kinetic rate of MXene@AgAu@PDA nanosheets under near-infrared irradiation increases from 0.13 to 0.69 min-1 mg-1. Density functional theory (DFT) is used to study the electron transfer behavior between AgAu nanocages and MXene nanosheets, and the mechanism of the enhanced catalytic reaction rate is analyzed. Besides, due to its Ag ions and photothermal coupling antibacterial properties, 40 µg mL-1 MXene@AgAu@PDA nanosheets inactivates nearly all E. coli and S. aureus after irradiation with near-infrared light for 6 min.

NIR-induced improvement of catalytic activity and antibacterial performance over AuAg nanorods in Rambutan-like Fe3O4@AgAu@PDA magnetic nanospheres.

Pathogenic bacteria and difficult-to-degrade pollutants in water have been serious problems that always plague people. Therefore, finding a "one stone-two birds" method that can quickly catalyze the degradation of pollutants and show effective antibacterial behavior become an urgent requirement. This work reports a facile one-step strategy for fabricating a Rambutan-like Fe3O4@AgAu@PDA (Fe3O4@AgAu@Polydopamine) core/shell nanosphere with both catalytic and antibacterial activities which can be critically improved by externally applying an NIR laser irradiation (NIR, 808 nm) and a rotating magnetic field. Typically, the Rambutan-like Fe3O4@AgAu@PDA nanosphere have a rather rough surface due to the AuAg bimetallic nanorods sandwiched between the Fe3O4 core and the PDA shell. Owing to the penetrated PDA shell, AgAu nanorods show high and magnetically recyclable photothermal-enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol and they can also be applied to initiate TMB oxidation under the help of NIR heating condition. Moreover, Fe3O4@AgAu@PDA shows a moderate antibacterial activity due to the weak release of Ag+. Under applying a rotating external magnetic field, the rough-surface Fe3O4@AgAu@PDA nanospheres produce a controllable magnetolytic force on the bacterial due to their good affinity. As a result, the Fe3O4@AgAu@PDA nanospheres show a "magnetolytic-photothermal-Ag+" synergistic antibacterial behavior against E. coli and S. aureus.

AgPd nanocages sandwiched between a MXene nanosheet and PDA layer for photothermally improved catalytic activity and antibacterial properties.

In this work, a MXene@AgPd/polydopamine (PDA) nanosheet with excellent photothermal conversion efficiency was successfully synthesized by a simple redox-oxidative polymerization method. Interestingly, AgPd bimetallic nanocrystals sandwiched between a MXene nanosheet and PDA layer have cage-like nanostructure, which is favorable for high catalytic efficiency and antibacterial performance. Importantly, the MXene@AgPd/PDA nanosheet exhibits good catalytic activity for the reduction of 4-nitrophenol (1.2 min-1 mg-1) and the catalytic dynamics can be improved by about 1.2 times under NIR (near-infrared light, 808 nm, and 2.5 W cm-2) irradiation. As the PDA shell is well protected, the MXene@AgPd/PDA nanosheet retained more than 90% catalytic activity after 6 cycles. In addition, due to the presence of the Ag component, the MXene@AgPd/PDA nanosheet exhibited good antibacterial activity against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Under near-infrared light irradiation, its antibacterial activity was further enhanced due to the NIR photothermal effect.

A Simple-Structured Perovskite Wavelength Sensor for Full-Color Imaging Application.

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI3/Au photodetectors on an MAPbI3 single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI3 single crystals. The high-performance MAPbI3 wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.

Magnetic-Field-Induced Improvement of Photothermal Sterilization Performance by Fe3O4@SiO2@Au/PDA Nanochains.

Due to the abuse of antibiotics, the sensitivity of patients to antibiotics is gradually reduced. This work develops a Fe3O4@SiO2@Au/PDA nanochain which shows an interesting magnetic-field-induced improvement of its photothermal antibacterial property. First, SiO2 was wrapped on Fe3O4 nanospheres assembled in a chain to form a Fe3O4@SiO2 nanocomposite with a chain-like nanostructure. Then, the magnetic Fe3O4@SiO2@Au/PDA nanochains were prepared using in situ redox-oxidization polymerization. Under the irradiation of an 808 nm NIR laser, the temperature rise of the Fe3O4@SiO2@Au/PDA nanochain dispersion was obvious, indicating that they possessed a good photothermal effect. Originating from the Fe3O4, the Fe3O4@SiO2@Au/PDA nanochain showed a typical soft magnetic behavior. Both the NIR and magnetic field affected the antimicrobial performance of the Fe3O4@SiO2@Au/PDA nanochains. Escherichia coli and Staphylococcus aureus were used as models to verify the antibacterial properties. The experimental results showed that the Fe3O4@SiO2@Au/PDA nanochains exhibited good antibacterial properties under photothermal conditions. After applying a magnetic field, the bactericidal effect was further significantly enhanced. The above results show that the material has a broad application prospect in inhibiting the growth of bacteria.

Near-infrared light-responsive photothermal α-Fe2O3@Au/PDA core/shell nanostructure with on-off controllable anti-bacterial effects.

Antimicrobial materials are expected to be alternatives for antibiotics against multidrug-resistant bacteria. In this paper, non-spherical α-Fe2O3@Au/PDA core/shell nanoparticles with tunable shapes are synthesized by a one-step in situ oxidation-redox polymerization method toward near infrared light-responsive antibacterial therapy. The thickness and composition of the Au/PDA hybrid shell can be controlled by varying the concentration of HAuCl4 and the dopamine precursor. Owing to the wonderful photothermal characteristics originating from the Au/PDA shell, the spindle α-Fe2O3@Au/PDA core shell nanoparticles exhibit excellent photothermal sterilization effects against both Escherichia coli and Staphylococcus aureus at low concentrations. Meanwhile, the NIR photothermal induced bactericidal performance indicates that α-Fe2O3@Au/PDA hybrid particles with tunable non-spherical shapes possess unique controllable antibacterial effects. As a result, this finding provides a simple strategy for fabricating high performance photothermal antibacterial agents and the final products possess high potential in synergistic antimicrobial therapy.

Hybrid Polydopamine/Ag Shell-Encapsulated Magnetic Fe3O4 Nanosphere with High Antibacterial Activity.

The bacteria, which usually contaminate water environment, often cause terrible infectious diseases thus seriously threaten people's health. To meet the increasing requirement of the public health care, an easily separable nanomaterial with sustainable anti-bacteria performance is required. This work reports a Fe3O4@PDA/Ag/PDA core-shell nanosphere in which the Ag nanocrystals immobilized on the magnetic carrier are protected by an external polydopamine (PDA) layer. The magnetic hybrid nanospheres are constructed by a tunable coating method and the particle parameters can be effectively controlled by the experimental condition. The antibacterial potential of the nanospheres is evaluable by using the Staphylococcus aureus and Escherichia coli as the models. The results indicate the Fe3O4@PDA/Ag/PDA core-shell nanospheres have a high antibacterial performance by measuring the minimum inhibitory concentration and the minimum bactericidal concentration. Finally, the product is expected to have a sustainable activity because the protecting PDA layer reduce the releasing rate of the Ag+ ions and the materials can be magnetically recovered from the media after the disinfection procedure.

A facile synthesis of one-dimensional hierarchical magnetic metal silicate microtubes with enhanced adsorption performance.

One-dimensional (1D) hierarchical magnetic hollow micro/nanotubes have attracted special attention in the field of adsorption owing to their high surface area, easy separation and short mass diffusion. Here, we report a facile approach for synthesizing one-dimensional hierarchical magnetic metal silicate microtubes through an extended Stöber method, carbonization treatment and subsequent hydrothermal reaction with metal ions in an alkaline solution. The unique 1D hierarchical magnetic microtubes have a large surface area, good structural stability and high magnetic response. Benefiting from these advantages, the resultant microtubes display excellent performance as good adsorbents for bovine hemoglobin (BHb) and methylene blue (MB). Furthermore, this strategy can also be applied to prepare other 1D hierarchical magnetic metal silicate composites.

Polydopamine protected hollow nanosphere with AuAg-nanoframe-core@Carbon@AuAg-nanocrystals-satellite hybrid nanostructure (AuAg@C@AuAg/PDA) for enhancing nanocatalysis.

This work reported a facile method for fabricating multi-layered polydopamine (PDA) encapsulated AuAg@C@AuAg core/shell nanosphere with a hollow interior. During the synthetic process, the preliminary Ag@C nanosphere is easily covered by an AuAg/PDA hybrid layer through the in situ redox-oxidized polymerization to form the Ag-AuAg@C@AuAg/PDA precursor, in which the AuAg bimetallic nanocrystals are simultaneously obtained via the electrochemical substitution reaction. After etching the residue Ag core, the final AuAg@C@AuAg/PDA hybrid nanosphere is achieved and the inner AuAg shows a unique nanoframe-like nanostructure. The carbon shell plays an important role for the formation and structure evolution of the AuAg@C@AuAg/PDA, and the composition can be modulated by varying the polymerization process. Owing to the well distributed AuAg nanocrystals and inner AuAg nanoframes, the AuAg@C@AuAg/PDA shows better performance than Ag-AuAg@C@AuAg/PDA precursor in catalyzing 4-nitrophenol, and the rate constant (K) to catalyst weight ratio reaches as high as 3.63 min-1 •mg-1. As a result, this work not only offers a hybrid bi-metallic nanocatalyst with excellent performance, but also has valuable implications for compositional modulation of hollow interior multi-layered nanostructure in adsorption, drug delivery, and nanocatalysis.

In situ redox-oxidation polymerization for magnetic core-shell nanostructure with polydopamine-encapsulated-Au hybrid shell.

This work reports a facile one-step method for the fabricating Fe3O4@Au/polydopamine sandwich-like core-shell nanostructure, in which the Au/polydopamine (Au/PDA) hybrid shell is obtained via an in situ redox-oxidation polymerization between the HAuCl4 and dopamine. The content of Au nanocrystals, shell thickness, and particle sizes are tunable by varying the experimental parameters. Intriguingly, this general method can be applied for different functional nanostructures such as the ß-FeOOH@Au/PDA, SiO2@Au/PDA, and CNT@Au/PDA nanocomposites. A possible formation mechanism is proposed and it is found that the surface interaction plays a key role in determining the final nanostructure. The as-prepared Fe3O4@Au/PDA exhibited eminent catalytic activity on the reduction of 4-nitrophenol. Since the external PDA shell prevents the Au nanocrystals from leaching during the reduction, the cycling activity has been maintained as high as 95% after seven times of catalytic reaction.

Magnetically Separable Nanocatalyst with the Fe3O4 Core and Polydopamine-Sandwiched Au Nanocrystal Shell.

This work reports a novel Fe3O4@polydopamine/Au/polydopamine core/shell nanocomposite toward a magnetically separable nanocatalyst. Because the polydopamine (PDA) layer-sandwiched Au nanocrystals were prepared by a layer-by-layer method, the content of Au could be controlled by varying the Au shell number (such as burger-like Fe3O4@PDA/Au/PDA/Au/PDA). Fe3O4@PDA/Au/PDA exhibited excellent catalytic activity in reducing p-nitrophenol because the substrate could penetrate the PDA shell. Owing to the protection of the PDA shell, Fe3O4@PDA/Au/PDA presented higher cyclability than Fe3O4@PDA/Au. The activity of Fe3O4@PDA/Au/PDA maintained 95% after 7 cycles, while that of Fe3O4@PDA/Au was only 61%. The detailed cycling catalytic mechanism was investigated, and it was found that the catalytic rate of Fe3O4@PDA/Au/PDA/Au/PDA was faster than that of Fe3O4@PDA/Au/PDA because of the higher Au content. Interestingly, this method could be extended for other magnetic nanocomposites with two different kinds of noble metal nanocrystals integrated within one particle, such as Fe3O4@PDA/Au/PDA/Ag/PDA and Fe3O4@PDA/Au/PDA/Pd/PDA.

Rod-like ß-FeOOH@poly(dopamine)-Au-poly(dopamine) nanocatalysts with improved recyclable activities.

A novel rod-like ß-FeOOH@poly(dopamine)-Au-poly(dopamine) nanocomposite is developed for recyclable catalysis. Firstly, the rod-like ß-FeOOH template was coated in situ by a layer of poly(dopamine) (PDA) to form a core/shell nanostructure. Then the negatively charged Au nanocatalysts were well-immobilized onto the periphery of the ß-FeOOH@PDA nanorod. To protect the Au nanocrystals from leaching during the catalytic reactions, another PDA layer was coated onto the above particles to form a sandwich-like PDA-Au-PDA shell on the ß-FeOOH rod core. The reduction of Rhodamine B (RhB) was introduced as a model reaction to evaluate the catalytic activity of the as-prepared nanocomposites. It was found that the catalytic rate sharply increased with an increasing amount of the nanocatalyst. Benefitting from the thin outer layer of PDA, the recyclability of the nanocatalyst dramatically increased. After five times of catalytic reaction, the activity was maintained as high as 98.3%, while the ß-FeOOH@PDA-Au showed it to be retained at only 73.4%.

A facile ultrasonication assisted method for Fe3O4@SiO2-Ag nanospheres with excellent antibacterial activity.

To increase the monodispersity of magnetic hybrid nanocomposites, a novel ultrasonic method was introduced to synthesize uniform Fe3O4@SiO2-Ag nanospheres. The immobilized Ag nanocrystals were tunable by varying the experimental conditions. An antibacterial assay indicated that the Fe3O4@SiO2-Ag nanospheres exhibited excellent antibacterial activities against Staphylococcus aureus and Escherichia coli, in which the minimum inhibition concentrations (MIC) were 40 µg mL(-1) and 20 µg mL(-1), respectively. The live/dead bacterial cell fluorescence stain assay agreed well with the antibacterial assay. The CCK-8 results indicated these nanospheres were bio-compatible for human normal cells and presented relative cytotoxicity against HepG2 tumor cells. These nanospheres could be easily uptaken by the cells and they could affect bacterial cells both inside and outside the cell membrane, which enable them to be promisingly applied in future biomedical areas.

Monodisperse magnetic core/shell microspheres with Pd nanoparticles-incorporated-carbon shells.

This work reports a hard self-template method to synthesize core/shell like Fe3O4@C microparticles, in which the Pd nanocrystals can be alternatively incorporated into the carbon shells. The Fe3O4@polyaniline core/shell microspheres were first synthesized as the precursor by in situ polymerization of aniline onto the surface of the Fe3O4 microspheres. In a subsequent carbonization of the precursor under a vacuum oven, the Fe3O4 core was preserved and the polyaniline shell transferred into carbon shells enveloping the magnetic sphere, forming magnetic Fe3O4@C microspheres. The Pd ions could be impregnated into the polyaniline shell, and thus the obtained composites were transformed into Fe3O4@C/Pd microspheres under the same vacuum heating progress. The as-obtained system demonstrates superparamagnetic characteristics, which would benefit its potential application in nanocatalysts. This strategy provides an efficient approach for tailoring core/shell materials with desired functionalities and structures by adjusting the precursors and structure-directing agents.

High-performance nonvolatile Al/AlO(x)/CdTe:Sb nanowire memory device.

Here we demonstrate a room temperature processed nonvolatile memory device based on an Al/AlO(x)/CdTe:Sb nanowire (NW) heterojunction. Electrical analysis shows an echelon hysteresis composed of a high-resistance state (HRS) and a low-resistance state (LRS), which can allow it to write and erase data from the device. The conductance ratio is as high as 106, with a retention time of 3 × 104 s. Moreover, the SET voltages ranged from +6 to +8 V, whilst the RESET voltage ∼0 V. In addition, flexible memory nano-devices on PET substrate with comparable switching performance at bending condition were fabricated. XPS analysis of the Al/AlO(x)/CdTe:Sb NW heterojunction after controlled Ar⁺ bombardment reveals that this memory behavior is associated with the presence of ultra-thin AlO(x) film. This Al/AlO(x)/CdTe:Sb NW heterojunction will open up opportunities for new memory devices with different configurations.

Asymmetric PSt-EA/Ni-Silicate hollow microsphere with a hierarchical porous shell.

Novel asymmetric hollow microspheres with polystyrene-ethylacrylate (PSt-EA) semi-spherical cores and porous hierarchical Ni-Silicate shells have been successfully fabricated by the combination of emulsifier-free polymerization, a modified Stöber method and an in situ hydrothermal conversion reaction. During the conversion of the PSt-EA@SiO2 core/shell microspheres to the asymmetric PSt-EA/Ni-Silicate composite, the spherical PSt-EA was melted within the hollow Ni-Silicate interior to form semi-microspheres. Upon further treating the asymmetric hollow microspheres by 500 °C calcination for 5 h, hierarchical Ni-Silicate hollow spheres were obtained. The BET area of the asymmetric hollow PSt-EA/Ni-Silicate microspheres was 58.9 m2 g-1 and the pore diameter was about 10-20 nm. The large porous nature of the products enable them be used as carriers for bio-molecules, and experiments indicated that the maximum adsorption ability of the asymmetric hollow microspheres could reach 8.2 µmol g-1 when the concentration of Cytochrome C was 200 mmol L¬1.

Inverted opal fluorescent film chemosensor for the detection of explosive nitroaromatic vapors through fluorescence resonance energy transfer.

This paper reports an inverted opal fluorescence chemosensor for the ultrasensitive detection of explosive nitroaromatic vapors through resonance-energy-transfer-amplified fluorescence quenching. The inverted opal silica film with amino ligands was first fabricated by the acid-base interaction between 3-aminopropyltriethoxysilane and surface sulfonic groups on polystyrene microsphere templates. The fluorescent dye was then chemically anchored onto the interconnected porous surface to form a hybrid monolayer of amino ligands and dye molecules. The amino ligands can efficiently capture vapor molecules of nitroaromatics such as 2,4,6-trinitrotoluene (TNT) through the charge-transfer complexing interaction between electron-rich amino ligands and electron-deficient aromatic rings. Meanwhile, the resultant TNT-amine complexes can strongly suppress the fluorescence emission of the chosen dye by the fluorescent resonance energy transfer (FRET) from the dye donor to the irradiative TNT-amino acceptor through intermolecular polar-polar resonance at spatial proximity. The quenching response of the highly ordered porous films with TNT is greatly amplified by at least 10-fold that of the amorphous silica films, due to the interconnected porous structure and large surface-to-volume ratio. The inverted opal film with a stable fluorescence brightness and strong analyte affinity has lead to an ultrasensitive detection of several ppb of TNT vapor in air.

Amine-capped ZnS-Mn2+ nanocrystals for fluorescence detection of trace TNT explosive.

Mn2+-doped ZnS nanocrystals with an amine-capping layer have been synthesized and used for the fluorescence detection of ultratrace 2,4,6-trinitrotoluene (TNT) by quenching the strong orange Mn2+ photoluminescence. The organic amine-capped nanocrystals can bind TNT species from solution and atmosphere by the acid-base pairing interaction between electron-rich amino ligands and electron-deficient aromatic rings. The resultant TNT anions bound onto the amino monolayer can efficiently quench the Mn2+ photoluminescence through the electron transfer from the conductive band of ZnS to the lowest unoccupied molecular orbital (LUMO) of TNT anions. The amino ligands provide an amplified response to the binding events of nitroaromatic compounds by the 2- to approximately 5-fold increase in quenching constants. Moreover, a large difference in quenching efficiency was observed for different types of nitroaromatic analytes, dependent on the affinity of nitro analytes to the amino monolayer and their electron-accepting abilities. The amine-capped nanocrystals can sensitively detect down to 1 nM TNT in solution or several parts-per-billion of TNT vapor in atmosphere. The ion-doped nanocrystal sensors reported here show a remarkable air/solution stability, high quantum yield, and strong analyte affinity and, therefore, are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.