Metallic Nanostructures Research Articles

Real-time monitoring of fast gas dynamics with a single-molecule resolution by frequency-comb-referenced plasmonic phase spectroscopy

Surface plasmon resonance (SPR) sensors are based on photon-excited surface charge density oscillations confined at metal-dielectric interfaces, which makes them highly sensitive to biological or chemical molecular bindings to functional metallic surfaces. Metal nanostructures further concentrate surface plasmons into a smaller area than the diffraction limit, thus strengthening photon-sample interactions. However, plasmonic sensors based on intensity detection provide limited resolution with long acquisition time owing to their high vulnerability to environmental and instrumental noises. Here, we demonstrate fast and precise detection of noble gas dynamics at single molecular resolution via frequency-comb-referenced plasmonic phase spectroscopy. The photon-sample interaction was enhanced by a factor of 3,852 than the physical sample thickness owing to plasmon resonance and thermophoresis-assisted optical confinement effects. By utilizing a sharp plasmonic phase slope and a high heterodyne information carrier, a small atomic-density modulation was clearly resolved at 5 Hz with a resolution of 0.06 Ar atoms per nano-hole (in 10–11 RIU) in Allan deviation at 0.2 s; a faster motion up to 200 Hz was clearly resolved. This fast and precise sensing technique can enable the in-depth analysis of fast fluid dynamics with the utmost resolution for a better understanding of biomedical, chemical, and physical events and interactions.

Surface Enhanced Nonlinear Raman Processes for Advanced Vibrational Probing.

Surface enhanced Raman scattering (SERS) is not restricted to the well-known one-photon excited spontaneous Raman process that gives information on molecular composition, structure, and interaction through vibrational probing with high sensitivity. The enhancement mainly originates in high local fields, specifically those provided by localized surface plasmon resonances of metal nanostructures. High local fields can particularly support nonlinear Raman scattering, as it depends on the fields to higher powers. By revealing plasmon-molecule interactions, nonlinear Raman processes provide a very sensitive access to the properties of metal nanomaterials and their interfaces with molecules and other materials. This Perspective discusses plasmon-enhanced spontaneous and coherent nonlinear Raman scattering with the aim of identifying advantages that lead to an advanced vibrational characterization of such systems. The discussion will highlight the aspects of vibrational information that can be gained based on specific advantages of different incoherent and coherent Raman scattering and their surface enhancement. While the incoherent process of surface enhanced hyper Raman scattering (SEHRS) gives highly selective and spectral information complementary to SERS, the incoherent process of surface enhanced pumped anti-Stokes Raman scattering (SEPARS) can help to infer effective nonresonant SERS cross sections and allows to see "hot" vibrational transitions. Surface enhanced coherent anti-Stokes Raman scattering (SECARS) and surface enhanced stimulated Raman scattering (SESRS) combine the advantages of high local fields and coherence, which gives rise to high detection sensitivity and offers possibilities to explore molecule-plasmon interactions for a comprehensive characterization of composite and hybrid structures in materials research, catalysis, and nanobiophotonics.

Fabrication of PSCs with light absorption chips utilizing double-metal-cladding waveguide technology

Metal nanoparticles or periodic metal nanostructures exhibit localized surface plasmon resonance (LSPR) effects, widely employed in photovoltaic devices to enhance the light absorption. In this study, we used a double-metal-cladding waveguide (DMCW) structure to fabricate hexagonal metal nanostructures on the front side of the indium tin oxide (ITO) glass, positioned away from the incident light direction. We then prepared perovskite solar cells under various reaction conditions. The analysis results indicate that the metal nanostructure chip excites near-field coupling, generating strong localized fields, and enhances the light absorption through the LSPR effect. The perovskite solar cells (PSCs) with the chip structures exhibited a significant increase in short-circuit current density (JSC) and fill factor (FF), accompanied by a decrease in dark current, indicating improved photovoltaic characteristics of the cells. Altering the evaporative deposition time of the silver film and the concentration of the reaction solution led to a 12.79% increase in the power conversion efficiency (PCE) of the PSCs.

Physical confinement versus adsorption driven reconstruction: The case of sulfate anion interaction with vicinal Cu(111) surfaces

Nano-electrochemistry, i.e., the research of the properties of nano-(structured) electrodes and their influence on electrochemical processes when immersed inside an electrolyte, represents a hot topic in view of applications in nano-electronics, electro-catalysis and energy storage devices. The role of physical confinement in the electrochemical fabrication and performances of the respective systems have been recently addressed in the context of metal-organic networks on surfaces, but rarely of nano-structured bare metal surfaces, for instance, regularly stepped (vicinal) surfaces. In this work we investigate the interplay between physical confinement and adsorbate induced restructuring by the electrochemical adsorption of sulfate anions on the flat and two distinctly different vicinal Cu(111) surfaces. Sulfate adsorption on the flat Cu(111) surface is known to create a long-range ordered Moiré-superstructure with lattice parameters in the 2–4 nm range due to an expansion of the topmost layer of copper atoms with respect to the underlying crystal planes. This restructuring is also observed on a vicinal Cu(111) surface whose original terrace width is considerably smaller than the lattice vectors of the sulfate induced Moiré-structure. The results clearly indicate not only that the Moiré formation lifts the physical confinement imposed by the initial terrace width, but also shine more light on the Moiré formation process itself. Such adsorbate induced restructuring, of course, depends on the respective adsorbate – electrode combination, but must, in principle, always be taken into account in order to understand electrochemical processes at nano-structured (and nano-sized) electrode surfaces.

(Invited) Plasmon-Driven Photochemistry for the Synthesis of Metal Nanostructures

Plasmon-driven photocatalysis with metal nanoparticles holds great promise for initiating and controlling chemical reactions at the nanoscale. One interesting application of plasmonic photochemistry involves the synthesis of metal nanostructures from cationic precursors. Despite more than twenty years of study however, this unique approach to material synthesis remains restricted to just two elements: silver (Ag) and gold (Au). To date, this process is yet to be observed with any other metals. Here, we report the plasmon-driven synthesis of copper (Cu) nanoparticles in aqueous solution via a seed-mediated growth strategy. The plasmonic synthesis is amenable to various Cu precursors, but is highly sensitive to the type of hole scavenger used in the reaction. We also found that the exclusion of oxygen from the system, both in the initial synthesis of Cu seeds and in their subsequent growth into larger nanoparticles, was essential for enabling the plasmon-driven process to proceed. A series of control experiments, supported by photoelectrochemical measurements, were performed to confirm that the growth of Cu nanoparticles occurs via plasmon excitation of the Cu seeds. Overall, our approach offers a unique route to the synthesis of Cu nanoparticles and expands the domain of plasmon-driven photochemistry to a new element.

(Invited) Changes in Electric Double-Layer Structures Under Localized Surface Plasmon Excitation

For the visible light energy conversion, the localized surface plasmon resonance (LSPR), which is the collective oscillations of free electrons, should be promising. With the excitation of LSPR, the highly localized electric field generates in the vicinity of metal nanostructures. It is interesting that various unique photo-response properties, such as chemical reactions or molecular excitations, can be observed due to the enhancement of light-matter interaction.[1] To understand and control such mediated chemical reactions or electrochemical reactions, the precise understanding about the electrified interfaces of plasmonic nanostructures should be required.Especially in the electrochemical system, the electric double layer is formed due to the difference in electrochemical potential between the metal interface and solution. The study of the surface potential is important for the design of chemical reactions because the surface potential at the liquid-solid interface is dependent on the physical properties of the systems. The zeta potential which is the potential of the slipping surface near the Stern layer of the diffusion layer could provide such information. From this point of view, in this study, we investigated the electric double-layer structures through the examination of the zeta potential under LSPR excitation condition. To obtain the zeta potential, we have performed the streaming potential method using Au nanoisland structures under visible light illuminations to excite the LSPR. It was interesting that the zeta potential was drastically changes under the visible light illumination conditions. This zeta potential change indicates the changes in the electric double layer structures through the excitation of LSPR. Through the investigations of incident wavelength dependence or the substrate dependences, the effects for the LSPR excitations on the electric double layer structure have been revealed. The present work would provide the fundamental knowledge about the effect on the LSPR excitation at solid-liquid interfaces.[1] H. Minamimoto et al., Acc. Chem. Res., 2022, 55(6), 809.

Synthesis of Plasmonic Copper/Copper Oxide Nanostructures as (Photo)Catalysts

Plasmonic nanostructures can enhance the photocatalytic efficiency of semiconductors under visible light irradiation. While the plasmonic-enhanced photocatalysis has been widely studied, rigorous efforts focus on designing novel noble metal nanostructures by altering particle size, shape, and composition to optimize their interaction with light to influence the catalytic properties. However, the need for a more cost-effective material as an alternative for noble metals has led us toward the exploration of copper and their oxides for photocatalysis. In this work, we synthesize different morphologies of copper nanostructures (i.e., 10 nm and 50 nm nanoparticles, as well as nanowires. Copper nanostructures are prone to be oxidized over time; however, the degree of oxidation varies with the size and shape of the nanostructure, thereby creating hybrid copper/copper oxide nanostructures with unique optical and (photo)catalytic properties. The hybrid nanostructures are characterized by X-ray powder diffraction and transmission electron microscopy. Their optical properties are studied by UV-vis spectroscopy along with simulation. We then further study the use of these hybrid nanostructures as (photo)catalysts for redox reactions – the reduction of 4-nitrophenol (4-NP) and the oxidation of tetramethylbenzidine (TMB). The (photo)catalytic properties will be correlated with the size, shape, and the degree of oxidation of these hybrid nanostructures. The mechanisms of both reactions on the hybrid copper/copper oxide (photo)catalysts will be discussed.

A Direct Dry Synthesis Route for High Purity Catalytic Nanoporous Metallic Films

Control of catalyst morphology is important because it affects many catalytic related properties such as, active sites, surface energy, and surface area, which can lead to tunable catalytic activity. Nanoporous metallic networks (NPMs), a morphology of interest for catalysis, contain many uncoordinated atoms at the surface and highly curved ligaments that can have a large effect on catalytic performance. Nanoporous self-supported metal structures have been synthesized in the past by dealloying of a master alloy,[1] which is a wet chemical method. This technique uses an Au-Ag alloy, from which Ag is etched away and which always results in NPMs containing residual amounts of the sacrificial metal (Ag) preventing the formation of high-purity structures. It follows that the catalytic properties of pure NPMs formed by dealloying can not be studied due to metal 'impurities' remaining in the structure. Although these 'impurities' contribute to catalytic activity and stability, it is difficult to control their amount and the systematic investigation of the 'impurity' effect is almost impossible for these NPMs.Here, we present results obtained by using physical vapor deposition, in the form of glancing angle deposition (GLAD), together with plasma etching to form nanoporous ultra-thin metal mesh structures, in a unique and facile dry synthesis method,[2] unlike most wet chemical synthesis methods used to prepare catalysts, which result chemical waste. The nanostructured metal mesh films are suitable for catalysis as they are extremely pure and highly porous, and contain high curvature ligaments, different crystal motifs, and many grain boundaries. We present nanoporous gold films (NPGF) prepared by our method as an example material. We show that the electrochemical structural stability of the NPGF is remarkably higher than that of dealloyed nanoporous gold, which is a result of the high amount of grain boundaries. Furthermore, the electrocatalytic performance of CH3OH oxidation is measured and the results show high catalytic activity for pure NPGF.[3] Our GLAD method can be applied to various metals and enables precise mixing or doping of different materials composing the NPMs. The high porosity, active sites, and potential elemental mixing will lead to new catalysts, especially suitable for CO2 reduction to fuels and value-added chemicals.[1] G. Wittstock, M. Bäumer, W. Dononelli, T. Klüner, L. Lührs, C. Mahr, L. V. Moskaleva, M. Oezaslan, T. Risse, A. Rosenauer, A. Staubitz, J. Weissmüller, A. Wittstock, Chem. Rev. 2023, 123, 6716.[2] H. Kwon, H.-N. Barad, A. R. Silva Olaya, M. Alarcón-Correa, K. Hahn, G. Richter, G. Wittstock, P. Fischer, ACS Appl. Mater. Interfaces 2023, 15, 5620.[3] H. Kwon, H.-N. Barad, A. R. Silva Olaya, M. Alarcón-Correa, K. Hahn, G. Richter, G. Wittstock, P. Fischer, ACS Catal. 2023, 11656.

Novel Approach of Nanophotonic Electron Transfer for Augmenting Photosynthesis in Arachis hypogaea: A Biophysical Rationale behind the Plasmonic Enhancement of Chemical Energy Transfer.

Plant photosynthetic machinery is the main source of acquisition and conversion of solar energy to chemical energy with the capacity for autonomous self-repair. However, the major limitation of the chloroplast photosystem is that it can absorb light only within the visible range of the spectrum, which is roughly 50% of the incident solar radiation. Moreover, the photosynthetic apparatus is saturated by less than 10% of available sunlight. If the capacity of solar light absorption and the transmission of resulting photons through the photosynthetic electron transport chain (ETC) can be extended, the overall efficiency of photosynthesis can be improved. The plant nanobionic approach can address this via the introduction of nanoparticles into or in the vicinity of the photosynthetic machinery/chloroplast. We have studied this exceptional nanobionic-mediated capability of two optically active nanostructures and evaluated the impact of their optical properties on plant photosynthesis. Our study revealed that metal (Ag) and core-shell metal nanostructures (AgS) can increase light absorption and improve electron transport through ETC. Both nanostructures were found to have a beneficial effect on the photoluminescence property of the isolated chloroplast. Translocation studies confirmed systemic transportation of the nanomaterial in different plant tissues. The primary growth parameters showed no detrimental effect until 21 days of treatment on Arachis hypogaea. The nano silver/silica core/shell structure (AgS) was found to be more advantageous over nano silver (AgNP) in photon entrapment, light-dependent biochemical reactions, and toxicity parameters. In the future, these nanostructures can enhance photosynthesis by increasing light absorption and resulting in higher assimilatory power generation in the form of ATP and NADPH. This approach may lead to a paradigm shift toward a sustainable method for the configuration of plant chloroplast-based hybrid energy harvesting devices.

Electroless Deposition of Noble Metals on Rod-Shape Plant Viruses in Various Aqueous Metal Precursor Solutions.

The challenge of synthesizing noble metal nanostructures sustainably has encouraged researchers to explore biological routes for nanostructure production, such as biotemplating. Plant viruses with rod-shape morphology, such as tobacco mosaic virus (TMV) and barley stripe mosaic virus (BSMV), offer promising biotemplates to produce metal nanorods. TMV and BSMV can be incubated in aqueous metal precursor solutions to mineralize metals on the coat proteins (CPs) of the viruses. Previous studies have primarily examined palladium (Pd) mineralization on TMV and BSMV using Na2PdCl4 as the Pd precursor. There is limited scientific literature on the effect of using alternative Pd precursor solutions besides Na2PdCl4 such as K2PdCl4 and PdCl2 to mineralize Pd on TMV and BSMV. Past attempts at mineralizing other noble metals such as platinum (Pt) and gold (Au) required an initial layer of Pd to be deposited on the TMV and BSMV biotemplates. In this study, we aimed to expand the understanding of using alternative Pd precursor solutions to mineralize Pd on TMV and BSMV. Additionally, the deposition of Pt and Au onto TMV and BSMV without the need for an initial Pd mineralization layer was achieved using alternative Pt and Au precursors, including K2PtCl4 and AuCl3, respectively. Pd, Pt, and Au were successfully deposited on TMV and BSMV by incubation in aqueous solutions of Na2PdCl4, K2PdCl4, PdCl2, K2PtCl4, and AuCl3. Kinetic studies were also conducted using ultraviolet-visible (UV-vis) spectroscopy to examine the rates at which Pd, Pt, and Au precursor ions were reduced during the mineralization process, mimicking their adsorption onto TMV and BSMV CPs. BSMV adsorbed noble metal precursor ions faster than TMV as determined by UV-vis spectroscopy. While palladium nanorods (PdNRs) offer high electrical conductivity desirable for electronic applications, Pd-coated TMV and BSMV may face limitations due to their organic cores, potentially compromising conductivity. To address this, one approach is to convert the organic core into conductive amorphous carbon through thermal annealing. In this study, in situ transmission electron microscopy was utilized to thermally anneal Pd-TMV2Cys, thereby transforming them into PdNRs with amorphous carbon cores.

Hyaluronic acid mediated ZnO-NPs: In relation to electrical and photocatalytic activity for dye degradation

Various processes have been implemented to purify water; however, photocatalysis is comprehensively utilized in wastewater treatment and plays a significant role in water remediation. A photocatalyst is a nanostructured metal oxide ZnO nanoparticles, which boosts the reaction rate by its existence. ZnO nanoparticles show great performance in the absorption of various organic pollutants from wastewater. The objective of this research was to enhance the photocatalytic degradation performance of HA-added ZnO NPs using methylene blue as a model wastewater. Adjusting the main physical properties and photocatalytic efficiency of ZnO-NPs was performed using hyaluronic acid (HA), a natural bioactive stabilizer. The characterization of the fabricated ZnO-NPs samples with and without HA involved the utilization of FE-SEM, AFM, XRD, FTIR, PL, and I-V. As demonstrated by the FE-SEM analysis, ZnO formed rod-like structures, 3.0 % HA:ZnO exhibited cauliflower-like structures, and 5.0 % HA:ZnO displayed honeycomb-like structures. The X-ray diffraction (XRD) analysis demonstrated that the HA:ZnO nanoparticles exhibited hexagonal wurtzite structures. The average crystallite sizes of the ZnO, 3.0 % HA:ZnO, and 5.0 % HA:ZnO NPs were determined to be 25.20, 27.30, and 20.20 nm, respectively, using the XRD patterns. The surface area was 4.439, 2.987, and 5.204 m²/g of bare ZnO, 3.0 % HA:ZnO, and 5.0 % HA:ZnO-NPs were 4.439, 2.987, and 5.204 m2/g, respectively. It is very likely that there are two different decay and/or capture mechanisms in the emission spectra because the TRPL decay profile behaves in a double-exponential way. The fast decay time constant (τ1) was 212 ps for bare ZnO and 3.0 % HA:ZnO NPs and 231 ps for 5.0 % HA:ZnO NPs. The slow decay time constant (τ2) has a similar pattern, with values of 3.716, 2.836, and 2.984 ns. The specific contact resistance values of the ZnO NPs increased from 0.113 to 45.624 ( × 105 Ω cm2) as a function of the HA concentration, as evidenced by the results of the electrical studies. The outcomes of this research present comprehensive information on noble-modified ZnO-NP materials containing HA for direct applications in electronic materials and photocatalytic degradation of organic waste in water.

Enhancing red-light emission of CsPb(Br/I)3 quantum dots through noble metal nanostructure-mediated localized surface plasmon resonance

The luminescence properties of perovskite quantum dots are crucial for their applications in various optoelectronic devices. Enhancing the luminescence performance of CsPb(Br/I)3 quantum dots is a critical challenge for their application in optoelectronic devices. This paper explores the use of noble metal nanostructures to improve the luminescence intensity of these quantum dots through localized surface plasmon resonance (LSPR). We conducted electric field simulations to optimize the LSPR effect and prepared Au@Ag@SiO2 nanobipyramids with tailored LSPR peaks. The nanobipyramids were then connected to CsPbCl2Br, CsPbBr3, and CsPbBrI2 quantum dots using amine-functionalized SiO2 layers, forming a nanocomposite that showed a significant increase in luminescence. The study identifies the importance of the SiO2 spacer layer in preventing luminescence quenching and demonstrates that the LSPR effect can be harnessed to achieve up to a 15-fold enhancement in luminescence intensity. This research provides a promising avenue for advancing the efficiency of solar energy harvesting devices, light-emitting devices, and optical detectors.

Electric tuning of plasmonic resonances in ultrathin gold nanoribbon arrays

Ultrathin plasmonic nanostructures offer an unparalleled opportunity for the study of light–matter interactions at the nanoscale and realization of compact nanophotonic devices. In this study, we introduce an ultrathin gold nanoribbon array and demonstrate an electric approach to actively tuning its plasmonic resonance, which leveraging the extreme light confinement capability in the ultrathin plasmonic nanostructure and a robust nanoscale electro-optical effect in indium tin oxide. Optimizing the design (to a total thickness as small as 12 nm for a 2-nm-thick gold nanoribbon array), we numerically demonstrate a spectral shift in the plasmonic resonance up to 36 nm along with an approximately 16% change in the transmission at a gate voltage below 1.7 V at the wavelength of 1.47 μm. This work presents progress towards electric tuning of plasmonic resonances in ultrathin metallic nanostructures for various applications including surface-enhanced spectroscopy, spontaneous emission enhancement, and optical modulation.

Enhancing THz radiation by optimizing the dimensioning of metallic nanostructures

A scheme of nonlinear terahertz (THz) radiations from gas atoms in spatially inhomogeneous fields induced by an intense monochromatic laser and an array of bow-tie shaped metallic nanostructures is proposed and theoretically investigated. Our simulations are based on the finite-difference time-domain method (FDTD) and time-dependent Schrödinger equations. The results demonstrate that the collective motion of ionized electrons within the inhomogeneous field generates intense transient currents. Asymmetrical electron motion leads to a net current, thereby generating strong THz radiation. By modulating the geometric dimensions of the metallic nanostructures, control over the distribution of the inhomogeneous field is achieved, enabling modification of the generated THz radiation.

New nano-complexes targeting protein 3S7S in breast cancer and protein 4OO6 in liver cancer investigated in cell line

Cancer, a lethal ailment, possesses a multitude of therapeutic alternatives to combat its presence, metal complexes have emerged as significant classes of medicinal compounds, exhibiting considerable biological efficacy, especially as anticancer agents. The utilization of cis-platin in the treatment of various cancer types, including breast cancer, has served as inspiration to devise novel nanostructured metal complexes for breast cancer therapy. Notably, homo- and hetero-octahedral bimetallic complexes of an innovative multifunctional ether ligand (comprising Mn(II), Ni(II), Cu(II), Zn(II), Hg(II), and Ag(I) ions) have been synthesized. To ascertain their structural characteristics, elemental and spectral analyses, encompassing IR, UV–Vis, 1H-NMR, mass and electron spin resonance (ESR) spectra, magnetic moments, molar conductance, thermal analysis, and electron microscopy, were employed. The molar conductance of these complexes in DMF demonstrated a non-electrolytic nature. Nanostructured forms of the complexes were identified through electron microscopic data. At ambient temperature, the ESR spectra of the solid complexes exhibited anisotropic and isotropic variants, indicative of covalent bonding. The ligand and several of its metal complexes were subjected to cytotoxicity testing against breast cancer protein 3S7S and liver cancer protein 4OO6, with the Ag(I) complex (7) evincing the most potent effect, followed by the Cu(II) with ligand (complex (2)), Cis-platin, the ligand itself, and the Cu(II)/Zn(II) complex (8). Molecular docking data unveiled the inhibitory order of several complexes.

Dynamic Ultrastrong Coupling in a 2 nm Gap Plasmonic Cavity at the Sub-Picosecond Scale.

Localized surface plasmon resonances (LSPRs) can enhance the electromagnetic fields on metallic nanostructures upon light illumination, providing an approach for manipulating light-matter interactions at the sub-wavelength scale. However, currently, there is no thorough investigation of the physical mechanism in the dynamic formation of the strongly coupled LSPRs on sub-5 nm plasmonic cavities at the sub-picosecond scale. In this work, through femtosecond broadband transient absorption spectroscopy, we reveal the dynamic ultrastrong coupling processes in a nanoparticle-in-trench (NPiT) structure containing 2 nm gap cavities, and demonstrate a coherent motional coupling between vibrating AuNPs and the nanogaps. We achieve a maximum Rabi splitting energy of ∼660 meV in the sub-picosecond hot-electron relaxation time scale under the resonant excitation of the nanogap cavity's LSPR, reaching the ultrastrong coupling regime. This leads to a change of global vibration modes for the 2 nm gap cavity, potentially related to the dynamical Casimir effect with nanogap resonators.

Identification of structural features of surface modifiers in engineered nanostructured metal oxides regarding cell uptake through ML-based classification.

Nanoparticles (NPs) are considered as versatile tools in various fields including medicine, electronics, and environmental science. Understanding the structural aspects of surface modifiers in nanoparticles that govern their cellular uptake is crucial for optimizing their efficacy and minimizing potential cytotoxicity. The cellular uptake is influenced by multiple factors, namely, size, shape, and surface charge of NPs, as well as their surface functionalization. In the current study, classification-based ML models (i.e., Bayesian classification, random forest, support vector classifier, and linear discriminant analysis) have been developed to identify the features/fingerprints that significantly contribute to the cellular uptake of ENMOs in multiple cell types, including pancreatic cancer cells (PaCa2), human endothelial cells (HUVEC), and human macrophage cells (U937). The best models have been identified for each cell type and analyzed to detect the structural fingerprints/features governing the cellular uptake of ENMOs. The study will direct scientists in the design of ENMOs of higher cellular uptake efficiency for better therapeutic response.

Gallium Nanostructure‐Based Microneedle Patch for Multidrug‐Resistant Bacterial Wound Healing: Enhanced Metal Release and NIR Photothermal Effect

AbstractBacterial infections, especially caused by multidrug‐resistant bacteria, pose a big challenge to the healthcare system. As a group of historic agents, metals with broad‐spectrum antibacterial activity are regarded as promising alternatives to tackle antibiotic resistance. Among them, gallium ions have presented encouraging antibacterial effects in research and preclinic studies. However, utilization of gallium ions has difficulty in achieving high targeting and long‐term effectiveness. With the renaissance of liquid metal, here, a novel and facile antibacterial gallium nanostructure is proposed in which polydopamine‐modified gallium nanocore serves as an ion reservoir for enhanced metal ion release and the surface also permits secondary reaction, allowing for in situ formation of Ag nanoparticles to improve the antibacterial property, ROS generation, and photothermal performance. Notably, ≈100% bacterial killing efficacy can be achieved when combined with NIR laser irradiation. The in vivo treatment results of methicillin‐resistant Staphylococcus aureus (MRSA)‐infected mice demonstrate that the microneedle patch loaded with nanoparticles exhibits outstanding bacterial elimination and inflammation alleviation, and promotes angiogenesis and collagen deposition, further accelerating wound healing. This gallium‐based nanostructure offers an effective nanoplatform for antibacterial treatments and combinatory strategies, which holds significant promise for refractory multidrug‐resistant bacteria and related infections.

Surface-Enhanced Raman Spectroscopy (SERS)-Based Sensors for Deoxyribonucleic Acid (DNA) Detection.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a powerful technique for the detection and analysis of biomolecules due to its high sensitivity and selectivity. In recent years, SERS-based sensors have received significant attention for the detection of deoxyribonucleic acid (DNA) molecules, offering promising applications in fields such as medical diagnostics, forensic analysis, and environmental monitoring. This paper provides a concise overview of the principles, advancements, and potential of SERS-based sensors for DNA detection. First, the fundamental principles of SERS are introduced, highlighting its ability to enhance the Raman scattering signal by several orders of magnitude through the interaction between target molecules with metallic nanostructures. Then, the fabrication technologies of SERS substrates tailored for DNA detection are reviewed. The performances of SERS substrates previously reported for DNA detection are compared and analyzed in terms of the limit of detection (LOD) and enhancement factor (EF) in detail, with respect to the technical parameters of Raman spectroscopy (e.g., laser wavelength and power). Additionally, strategies for functionalizing the sensor surfaces with DNA-specific capture probes or aptamers are outlined. The collected data can be of help in selecting and optimizing the most suitable fabrication technology considering nucleotide sensing applications with Raman spectroscopy.

Flexible plasmonic display featuring differentiated and localized control over transmission and reflection

Structural colors using metal materials, plasmonic color generation, can confine optical excitation beyond the diffraction limit owing to nanoscale metals with high efficiency in light absorption and scattering. They have several advantages over conventional display technology, including superior resolution and long-term preservation. However, most research on plasmonic color generation has been conducted for the development of static color generation, and dynamic tuning remains a challenging issue. To develop dynamic plasmonic colors, electrochemical, liquid crystal, and electromechanical methods have been proposed; however, there have been limitations in repeatability, flexibility, and scale-up processes. To address these problems, this work proposes a flexible dynamic plasmonic display using dielectric elastomer actuators (DEAs) to isotropically control the interdistance between the metal nanostructures, which can show dynamic coloration without polarization distortion. To replace the expensive and small-scale manufacturing approach, shadow masking and transfer technique with the anodic aluminum oxide (AAO) membrane was applied to realize large-scale and uniformly distributed Au nanodisc array. The differentiated and localized color change in the transmission and reflection modes, such as Janus's face, is realized by proper design of Au nanodisc array on the patterned transparent compliant electrodes formed by silver nanowires and PEDOT:PSS composites. Apparent and locally active color changes appeared in the transmission mode, but almost no color changes were observed in the reflection model by DEA actuation. The proposed system has the potential to activate color filters, cryptographic characters, and next generation display technologies.