Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

Photothermal Heating-Assisted Superior Antibacterial and Antibiofilm Activity of High-Entropy-Alloy Nanoparticles

Antibacterial elements and non-contact heating abilities have been proven effective for antibacterial and antibiofilm activities, but it remains a challenge to integrate both within one material. Herein, assisted by the high-entropy effect, FeNiTiCrMnCu_x high-entropy alloy nanoparticles (HEA-NPs) with excellent photothermal heating properties for boosting antibacterial and antibiofilm performances are synthesized. Benefitting from the synergetic effect of copper ions released and thermal damage by the HEA-NPs, more reactive oxygen species (ROS) are generated, leading to the rupture of the cell membranes and the eradication of the biofilms. As a result, the antibiofilm efficiency (400 µg mL⁻¹) of the mostly optimized FeNiTiCrMnCu_1.0 HEA-NPs in the marine nutrient medium, which is the worst-case scenario for the antimicrobial material, can be improved from 81% to 97.4% under 30 min solar irradiation (1 sun). The present study demonstrates a new strategy for effectively treating marine microorganisms that cause biofouling and microbial corrosion using HEA-NPs with photothermal heating characteristics as an antibacterial auxiliary.     

A Zn‐Doped CuO Nanocomposite Shows Enhanced Antibiofilm and Antibacterial Activities Against Streptococcus Mutans Compared to Nanosized CuO

Zinc‐doped copper oxide and copper oxide nanoparticles (NPs) are synthesized and deposited on artificial teeth by sonic irradiation, and the ability of these coatings to restrict biofilm formation by Streptococcus mutans is examined. The CuO and Zn:CuO NP‐coated teeth show significant reductions in biofilm formation of 70% and 88%, respectively, compared to uncoated teeth. The mechanism of the Zn:CuO nanoparticles is investigated, revealing that the nanoparticles attach to and penetrate the bacteria and generate intracellular reactive oxygen species (ROS) that enhance lipid peroxidation and cause cell death. Conversely, the CuO or ZnO NPs do not show this behavior and could not generate intracellular ROS. These results highlight the superior efficacy of Zn:CuO nanocomposites over CuO and ZnO NPs and the role of ROS in their antimicrobial effect.     

A Melanin‐Based Natural Antioxidant Defense Nanosystem for Theranostic Application in Acute Kidney Injury

Acute kidney injury (AKI) is frequently associated with oxidative stress and causes high mortality annually in clinics. Nanotechnology‐mediated antioxidative therapy is emerging as a novel strategy for the treatment of AKI. Herein, a novel biomedical use of the endogenous biopolymer melanin as a theranostic natural antioxidant defense nanoplatform for AKI is reported. In this study, ultrasmall Mn²⁺‐chelated melanin (MMP) nanoparticles are easily prepared via a simple coordination and self‐assembly strategy, and further incorporated with polyethylene glycol (MMPP). In vitro experiments reveal the ability of MMPP nanoparticles to scavenge multiple toxic reactive oxygen species (ROS) and suppress ROS‐induced oxidative stress. Additionally, in vivo results from a murine AKI model demonstrate preferential renal uptake of MMPP nanoparticles and a subsequent robust antioxidative response with negligible side effects according to positron emission tomography/magnetic resonance (PET/MR) bimodal imaging and treatment assessment. These results indicate that the effectiveness of MMPP nanoparticles for treating AKI suggests the potential efficacy of melanin as a natural theranostic antioxidant nanoplatform for AKI, as well as other ROS‐related diseases.     

Dual‐Mechanism Antimicrobial Polymer–ZnO Nanoparticle and Crystal Violet‐Encapsulated Silicone

The prevalence of healthcare‐associated infection caused by multidrug‐resistant bacteria is of critical concern worldwide. It is reported on the development of a bactericidal surface prepared by use of a simple, upscalable, two‐step dipping strategy to incorporate crystal violet and di(octyl)­phosphinic‐ acid‐capped zinc oxide nanoparticles into medical grade silicone, as a strategy to reduce the risk of infection. The material is characterized by UV–vis absorbance spectroscopy, X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) and transmission electron microscopy (TEM) and confirmed the incorporation of the ZnO nanoparticles in the polymer. The novel system proves to be a highly versatile bactericidal material when tested against both Staphylococcus aureus and Escherichia coli, key causative micro‐organisms for hospital‐acquired infection (HAI). Potent antimicrobial activity is noted under dark conditions, with a significant enhancement exhibits when the surfaces are illuminated with a standard hospital light source. This polymer has the potential to decrease the risk of HAI, by killing bacteria in contact with the surface.     

Changes in Electrical Characteristics of ZnO Thin Films Due to Environmental Factors

The impact of light and controlled gas ambient on the electrical characteristics of ZnO:P grown by pulsed laser deposition (PLD) is investigated with temperature-dependent Hall-effect and photo-Hall-effect using above-bandgap light. Exposure to blue/ultraviolet (UV) light results in long-lived persistent photoconductivity (PPC) effects dominated by electron conduction. However, these persistent effects can be largely reversed by exposing the sample to a controlled ambient of dry O₂ gas. These O₂-induced changes in the electronic properties persist in vacuum up to at least 400 K. Exposure to dry N₂ gas following blue/UV light has no effect on the observed PPC characteristics. The implications of these effects on the preparation of p-type ZnO will be discussed.     

Polydisperse Aggregates of ZnO Nanocrystallites: A Method for Energy‐Conversion‐Efficiency Enhancement in Dye‐Sensitized Solar Cells

ZnO films consisting of either polydisperse or monodisperse aggregates of nanocrystallites were fabricated and studied as dye‐sensitized solar‐cell electrodes. The results revealed that the overall energy‐conversion efficiency of the cells could be significantly affected by either the average size or the size distribution of the ZnO aggregates. The highest overall energy‐conversion efficiency of ～4.4% was achieved with the film formed by polydisperse ZnO aggregates with a broad size distribution from 120 to 360 nm in diameter. Light scattering by the submicrometer‐sized ZnO aggregates was employed to explain the improved solar‐cell performance through extending the distance travelled by light so as to increase the light‐harvesting efficiency of photoelectrode film. The broad distribution of aggregate size provides the ZnO films with both better packing and an enhanced ability to scatter the incident light, and thus promotes the solar‐cell performance.     

Construction of Nanozyme‐Hydrogel for Enhanced Capture and Elimination of Bacteria

The widespread multidrug resistance resulting from the abuse of antibiotics motivates researchers to explore alternative methods to treat bacterial infections. Recently, the emergence of nanozymes has provided a potential approach to combat bacteria. Such nanozymes can mimic the functions of natural enzymes to induce the production of highly toxic reactive oxygen species (ROS) as an antibacterial. However, the lack of effective interaction between nanozymes and bacteria, and the intrinsic short lifetime and diffusion distance of ROS greatly compromise their bactericidal activity. Furthermore, the dead bacteria left in the infected area can give rise to unexpected tissue inflammation. Herein, for the first time, a nanozyme‐hydrogel is constructed to realize reinforced antibacterials. The nanozyme‐hydrogel with the traits of positive charge and macropore can capture and restrict bacteria in the range of ROS destruction. Significantly, by combining the near‐infrared photothermal property of nanozymes, the nanozyme‐hydrogel can achieve a synergistic bactericidal effect. More importantly, the nanozyme‐hydrogel can eliminate bacteria and reduce the risk of inflammation. In consequence, the current work manifests an original strategy to improve the antibacterial performance of nanozymes, concurrently promote wound healing.     

Supercritical‐Fluid‐Assisted One‐Pot Synthesis of Biocompatible Core(γ‐Fe2O3)/Shell(SiO2) Nanoparticles as High Relaxivity T2‐Contrast Agents for Magnetic Resonance Imaging

Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(γ‐Fe₂O₃)/shell(SiO₂), with a diameter of approximately 100 nm and a high magnetization are synthesized by combining sol–gel chemistry and supercritical fluid technology. This one‐step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T₂ MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation.     

Generic Strategy of Preparing Fluorescent Conjugated‐Polymer‐Loaded Poly(DL‐lactide‐co‐Glycolide) Nanoparticles for Targeted Cell Imaging

A general strategy for the preparation of highly fluorescent poly(DL‐lactide‐co‐glycolide) (PLGA) nanoparticles (NPs) loaded with conjugated polymers (CPs) is reported. The process involves encapsulation of organic‐soluble CPs with PLGA using a modified solvent extraction/evaporation technique. The obtained NPs are stable in aqueous media with biocompatible and functionalizable surfaces. In addition, fluorescent properties of the CP‐loaded PLGA NPs (CPL NPs) could be fine‐tuned by loading different types of CPs into the PLGA matrix. Four types of CPL NPs are prepared with a volume‐average hydrodynamic diameter ranging from 243 to 272 nm. The application of CPL NPs for bio‐imaging is demonstrated through incubation with MCF‐7 breast cancer cells. Confocal laser scanning microscopy studies reveal that the CPL NPs are internalized in cytoplasm around the nuclei with intense fluorescence. After conjugation with folic acid, cellular uptake of the surface‐functionalized CPL NPs is greatly enhanced via receptor‐mediated endocytosis by MCF‐7 breast cancer cells, as compared to that for NIH/3T3 fibroblast cells, which indicates a selective targeting effect of the folate‐functionalized CPL NPs in cellular imaging. The merits of CPL NPs, such as low cytotoxicity, high fluorescence, good photostability, and feasible surface functionalization, will inspire extensive study of CPL NPs as a new generation of probes for specific biological imaging and detection.     

Three‐Dimensional Kelvin Probe Microscopy for Characterizing In‐Plane Piezoelectric Potential of Laterally Deflected ZnO Micro‐/Nanowires

Potential characterization of deflected piezoelectric nanowires (NWs) is of great interest for current development of electromechanical nanogenerators that harvest ambient mechanical energy. In this paper, a Kelvin probe microscopy (KPM) technique hybridizing scanning KPM (SKPM) with atomic force microscope (AFM) surface‐approach spectroscopy methods for characterizing in‐plane piezoelectric potential of ZnO microwires (MWs) is presented. This technique decouples the scanning motion of the AFM tip from sample topography, and thus effectively eliminates artifacts induced by high topographical variations along the edges of MWs/NWs which make characterization by conventional SKPM inappropriate or impossible. By virtue of the topography/tip motion decoupling approach, the electrical potential can also be mapped in a three‐dimensional (3D) spatial volume above the sample surface. Therefore, this technique is named 3DKPM. Through 3DKPM mapping, the piezopotential generated by a laterally deflected ZnO MW was determined by extracting the potential asymmetry from opposite sides of the MW. The measurement results agree well with theoretical predictions. Integrating an external bias to the MW sample allowed direct observation of piezopotential and carrier concentration coupling phenomenon in ZnO, opening a door toward quantitative microscopic investigation of the piezotronic effect. With further positioning refinements, 3DKPM could become a powerful technique for the characterization of piezoelectric potential and related effects in micro/nanostructures of high topographical variations, as well as development of MW/NW‐based piezoelectric nanodevices.     

An O2 Self‐Supplementing and Reactive‐Oxygen‐Species‐Circulating Amplified Nanoplatform via H2O/H2O2 Splitting for Tumor Imaging and Photodynamic Therapy

Conventional photodynamic therapy (PDT) has limited applications in clinical cancer therapy due to the insufficient O₂ supply, inefficient reactive oxygen species (ROS) generation, and low penetration depth of light. In this work, a multifunctional nanoplatform, upconversion nanoparticles (UCNPs)@TiO₂@MnO₂ core/shell/sheet nanocomposites (UTMs), is designed and constructed to overcome these drawbacks by generating O₂ in situ, amplifying the content of singlet oxygen (¹O₂) and hydroxyl radical (?OH) via water‐splitting, and utilizing 980 nm near‐infrared (NIR) light to increase penetration depth. Once UTMs are accumulated at tumor site, intracellular H₂O₂ is catalyzed by MnO₂ nanosheets to generate O₂ for improving oxygen‐dependent PDT. Simultaneously, with the decomposition of MnO₂ nanosheets and 980 nm NIR irradiation, UCNPs can efficiently convert NIR to ultraviolet light to activate TiO₂ and generate toxic ROS for deep tumor therapy. In addition, UCNPs and decomposed Mn²⁺ can be used for further upconversion luminescence and magnetic resonance imaging in tumor site. Both in vitro and in vivo experiments demonstrate that this nanoplatform can significantly improve PDT efficiency with tumor imaging capability, which will find great potential in the fight against tumor.     

Polydisperse Spindle‐Shaped ZnO Particles with Their Packing Micropores in the Photoanode for Highly Efficient Quasi‐Solid Dye‐Sensitized Solar Cells

In this paper, a novel hierarchically structured ZnO photoanode for use in quasi‐solid state dye‐sensitized solar cells (DSCs) is presented. The film is composed of polydisperse spindle‐shaped ZnO particles that are prepared through direct precipitation of zinc acetate in aqueous solution. Without additional pore‐forming agents, the microporous structure is well constructed through the packing of polydisperse ZnO particles. In the film, small ZnO particles are able to improve interparticle connectivity and offer a large internal surface area for sufficient dye‐adsorption; on the other hand, particles of larger size can enhance the occurrence of light‐scattering and introduce micropores for the permeation of quasi‐solid state electrolytes. Meanwhile, morphologies, particle size, and specific areas of the products are controlled by altering the reactant concentration and synthetic temperature. Combined with a highly viscous polymer gel electrolyte, a device based on this ZnO photoanode shows high conversion efficiencies, 4.0% and 7.0%, under 100 and 30 mW cm^?2 illumination, respectively. Finally, the unsealed device is demonstrated to remain above 90% of its initial conversion efficiency after 7 days, showing excellent stability.     

A Unique Disintegration–Reassembly Route to Mesoporous Titania Nanocrystalline Hollow Spheres with Enhanced Photocatalytic Activity

A novel disintegration–reassembly route is reported for the synthesis of mesoporous TiO₂ nanocrystalline hollow spheres with controlled crystallinity and enhanced photocatalytic activity. In this unique synthesis strategy, it is demonstrated that sol–gel‐derived mesoporous TiO₂ colloidal spheres can be disintegrated into discrete small nanoparticles that are uniformly embedded in the polymer (polystyrene, PS) matrix by surface‐induced photocatalytic polymerization. Subsequent reassembly of these TiO₂ nanoparticles can be induced by an annealing process after further coating of a resorcinol–formaldehyde (RF) resin, which forms self‐supported hollow spheres of TiO₂ at the PS/RF interface. The abundant phenolic groups on the RF resin serve as anchoring sites for the TiO₂ nanoparticles, thus enable the reassembly of the TiO₂ nanoparticles and prevent their sintering during the thermal crystallization process. This unique disintegration–reassembly process leads to the formation of self‐supported TiO₂ hollow spheres with relatively large surface area, high crystallinity, and superior photocatalytic activity in dye degradation under UV light irradiation.     

Redox Capacitor to Establish Bio‐Device Redox‐Connectivity

Electronic devices process information and transduce energy with electrons, while biology performs such operations with ions and chemicals. To establish bio‐device connectivity, we fabricate a redox‐capacitor film from a polysaccharide (i.e., chitosan) and a redox‐active catechol. We report that these films are rapidly and repeatedly charged and discharged electrochemically via a redox‐cycling mechanism in which mediators shuttle electrons between the electrode and film (capacitance ≈ 40 F/g or 2.9 mF/cm²). Further, charging and discharging can be executed under bio‐relevant conditions. Enzymatic‐charging is achieved by electron‐transfer from glucose to the film via an NADPH‐mediated redox‐cycling mechanism. Discharging occurs by electron‐donation to O₂ to generate H₂O₂ that serves as substrate for peroxidase‐mediated biochemical reactions. Thus, these films offer the capability of inter‐converting electrochemical and biochemical inputs/outputs. Among potential applications, we anticipate that catechol–chitosan redox‐capacitor films could serve as circuit elements for molecular logic operations or for transducing bio‐based chemical energy into electricity.     

One‐Step Synthesis and Optical Properties of Benzoate‐ and Biphenolate‐Capped ZrO2 Nanoparticles

A simple one‐pot approach based on the “benzyl alcohol route” is used for the preparation of benzoate‐ and biphenolate‐capped zirconia and, benzoate‐capped Eu‐doped zirconia nanoparticles. Powder X‐ray diffraction studies and high‐ resolution transmission electron microscopy (HR‐TEM) showed that the nanoparticles present high crystallinity and uniform particle sizes ranging from 3 to 4 nm. FT‐IR and solid state NMR (SS‐NMR) studies revealed that the nanoparticles are coated with a large amount of organic species when the reaction temperature is above 300 °C. It was found that the alcohol used as solvent is oxidized at the surface of the nanoparticles to the respective carboxylic acid which acts as a stabilizer, controlling the nanoparticles growth. The optical properties of these hybrid nanoparticles were studied by room and low (12K) temperature photoluminescence spectroscopy, time‐resolved spectroscopy and absolute emission quantum yield. The as‐synthesized benzoate‐ and biphenolate‐capped nanoparticles exhibit interesting emission properties in the UV and blue spectral regions together with values of emission quantum yields much higher than those reported for zirconia nanoparticles of similar size. The photoluminescent properties were attributed to a cooperative effect of the capping ligands and the defects associated to the ZrO₂ nanoparticles. Due to the overlapping of the various emission components involved (i.e., the emission of europium(III) intra‐4f⁶ transitions, defects in the zirconia and capping ligands) a tunable emission color ranging from purplish‐pink to greenish‐blue could be obtained for the europium‐doped zirconia nanoparticles by simply selecting different excitation wavelengths.     

Conjugated Polyelectrolyte Hybridized ZnO Nanoparticles as a Cathode Interfacial Layer for Efficient Polymer Light‐Emitting Diodes

Alkoxy side‐chain tethered polyfluorene conjugated polyelectrolyte (CPE), poly[(9,9‐bis((8‐(3‐methyl‐1‐imidazolium)octyl)‐2,7‐fluorene)‐alt‐(9,9‐bis(2‐(2‐methoxyethoxy)ethyl)‐fluorene)] dibromide (F8imFO₄), is utilized to obtain CPE‐hybridized ZnO nanoparticles (NPs) (CPE:ZnO hybrid NPs). The surface defects of ZnO NPs are passivated through coordination interactions with the oxygen atoms of alkoxy side‐chains and the bromide anions of ionic pendent groups from F8imFO₄ to the oxygen vacancies of ZnO NPs, and thereby the fluorescence quenching at the interface of yellow‐emitting poly(p‐phenylene vinylene)/CPE:ZnO hybrid NPs is significantly reduced at the CPE concentration of 4.5 wt%. Yellow‐emitting polymer light‐emitting diodes (PLEDs) with CPE(4.5 wt%):ZnO hybrid NPs as a cathode interfacial layer show the highest device efficiencies of 11.7 cd A^?1 at 5.2 V and 8.6 lm W^?1 at 3.8 V compared to the ZnO NP only (4.8 cd A^?1 at 7 V and 2.2 lm W^?1 at 6.6 V) or CPE only (7.3 cd A^?1 at 5.2 V and 4.9 lm W^?1 at 4.2 V) devices. The results suggest here that the CPE:ZnO hybrid NPs has a great potential to improve the device performance of organic electronics.     

A Smart Nanoprobe Based On Fluorescence‐Quenching PEGylated Nanogels Containing Gold Nanoparticles for Monitoring the Response to Cancer Therapy

A biocompatible, caspase‐3‐responsive, and fluorescence‐quenching smart apoptosis nanoprobe based on a PEGylated nanogel that contains gold nanoparticles (GNPs) (fluorescence quenchers) in the cross‐linked polyamine gel core and fluorescein isothiocyanate (FITC)‐labeled DEVD peptides at the tethered PEG chain ends is prepared for monitoring the cancer response to therapy. FITC–DEVD–nanogel–GNP shows very little fluorescence in the absence of activated caspase‐3 (normal cells) through the fluorescence resonance energy transfer (FRET) process between the GNPs and the FITC molecules, while pronounced fluorescence signals are observed in apoptotic cells because of the cleavage of the DEVD peptide by activated caspase‐3 present in the cells, which results in the release of FITC molecules. Thus, remarkable quenching and dequenching of fluorescence signals in response to activated caspase‐3 is observed. Apoptotic cells are detected in human hepatocyte (HuH‐7) multicellular tumor spheroids (MCTSs), a commonly used three‐dimensional in vitro model mimicking the in vivo biology of tumors, as early as one day post‐treatment with staurosporine, an apoptosis‐inducing agent; while growth inhibition (i.e., change in size) of the HuH‐7 MCTSs is only observed after a delay of three days (i.e., on day 4). This demonstrates the effectiveness of the FITC–DEVD–nanogel–GNP probe as a smart nanoprobe for real‐time monitoring as well as a more rapid assessment of the early response to cancer therapy.