Promoting Plasmonic Hot Hole Extraction and Photothermal Effect for the Oxygen Evolution Reactions.

Boosting oxygen evolution reaction by local surface plasmon resonance (LSPR) provides breakthrough opportunities for the promotion of solar energy conversion; the potential of LSPR, however, has rarely been tapped and investigated. Here, we report the precise regulation of commercial Au nanoparticles plasmonic nanomaterial and OER electrocatalysts, viz., the NiCoOx electrocatalytic layer with hole transport ability and photothermal effect is prepared on the surface of Au nanoparticles by photoelectrodeposition. The NiCoOx layer not only increases the transmission distance of holes generated by plasmonic Au nanoparticles, but also reduce the agglomeration of plasmonic Au nanoparticles during long-time OER reaction, which greatly improves the OER catalytic ability. The current density of NiCoOx /Au anode achieves 16.58 mA cm-2 at 2.0 V versus RHE, which is about 6.5 times of pristine NiCoOx anode (2.56 mA cm-2 ) and 47 times of pristine Au anode (0.35 mA cm-2 ). More importantly, with the LSPR and photothermal effect of plasmonic Au nanoparticles, the NiCoOx /Au anode provides additional current density of 7.01 mA cm-2 after illumination, and maintains no attenuation for more than 2000 s. Benefiting from the solution of agglomeration problem of plasmonic Au nanoparticles in the long-time OER process and the effective utilization of generated holes of plasmonic Au nanoparticles, this design can provide guidance for the application of plasmonic materials in the field of electrocatalysis.

Steering the Pathway of Plasmon-Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer.

Photoelectrochemical (PEC) conversion of CO2 in an aqueous medium into high-energy fuels is a creative strategy for storing solar energy and closing the anthropogenic carbon cycle. However, the rational design of catalytic architectures to selectively and efficiently produce a target product such as CO has remained a grand challenge. Herein, an efficient and selective Si photocathode for CO production is reported by utilizing a TiO2 interlayer to bridge the Au nanoparticles and n+ p-Si. The TiO2 interlayer can not only effectively protect and passivate Si surface, but can also exhibit outstanding synergies with Au nanoparticles to greatly promote CO2 reduction kinetics for CO production through stabilizing the key reaction intermediates. Specifically, the TiO2 layer and Au nanoparticles work concertedly to enhance the separation of localized surface plasmon resonance generated hot carriers, contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during PEC CO2 reduction. The optimized Au/TiO2 /n+ p-Si photocathode exhibits a Faradaic efficiency of 86% and a partial current density of -5.52 mA cm-2 at -0.8 VRHE for CO production, which represent state-of-the-art performance in this field. Such a plasmon-enhanced strategy may pave the way for the development of high-performance PEC photocathodes for energy-efficient CO2 utilization.

Low-cost and simple fabrication of hierarchical Al nanopit arrays for deep ultraviolet refractive index sensing.

Herein, we proposed a simple non-lithographic way to fabricate hierarchical Al nanopit arrays performed as deep ultraviolet (DUV, 200-300 nm) refractive index sensing. Only by adjusting the Al deposition thickness on the Al nanopit array, the hierarchical Al nanopit arrays with tunable plasmonic properties in the DUV region were obtained. The prepared hierarchical Al nanopit arrays are of very good time stability and its RI sensitivity and concentration detection limit of adenine ethanol solution reach 311 nm/RIU and5×10-6M,respectively, as the Al deposition thickness is 60 nm. Furthermore, the electric field distribution simulation results show that high RI sensing characteristic are mainly attributed to the local surface plasmon resonance. This investigation provides a facile way to develop low cost, high efficient and easily fabricated Al-based RI sensor in the DUV region.

Spectral image contrast-based flow digital nanoplasmon-metry for ultrasensitive antibody detection.

BACKGROUND: Gold nanoparticles (AuNPs) have been widely used in local surface plasmon resonance (LSPR) immunoassays for biomolecule sensing, which is primarily based on two conventional methods: absorption spectra analysis and colorimetry. The low figure of merit (FoM) of the LSPR and high-concentration AuNP requirement restrict their limit of detection (LOD), which is approximately ng to µg mL-1 in antibody detection if there is no other signal or analyte amplification. Improvements in sensitivity have been slow in recent for a long time, and pushing the boundary of the current LOD is a great challenge of current LSPR immunoassays in biosensing. RESULTS: In this work, we developed spectral image contrast-based flow digital nanoplasmon-metry (Flow DiNM) to push the LOD boundary. Comparing the scattering image brightness of AuNPs in two neighboring wavelength bands near the LSPR peak, the peak shift signal is strongly amplified and quickly detected. Introducing digital analysis, the Flow DiNM provides an ultrahigh signal-to-noise ratio and has a lower sample volume requirement. Compared to the conventional analog LSPR immunoassay, Flow DiNM for anti-BSA detection in pure samples has an LOD as low as 1 pg mL-1 within only a 15-min detection time and 500 µL sample volume. Antibody assays against spike proteins of SARS-CoV-2 in artificial saliva that contained various proteins were also conducted to validate the detection of Flow DiNM in complicated samples. Flow DiNM shows significant discrimination in detection with an LOD of 10 pg mL-1 and a broad dynamic detection range of five orders of magnitude. CONCLUSION: Together with the quick readout time and simple operation, this work clearly demonstrated the high sensitivity and selectivity of the developed Flow DiNM in rapid antibody detection. Spectral image contrast and digital analysis further provide a new generation of LSPR immunoassay with AuNPs.

A multi-colorimetric immunosensor for visual detection of ochratoxin A by mimetic enzyme etching of gold nanobipyramids.

A multi-colorimetric immunosensor basing on the mimetic enzyme etching of gold nanobipyramids (Au NBPs) was established to detect ochratoxin A (OTA). Octahedral Cu2O nanoparticles were successfully synthesized through a selective surface stabilization strategy, which can exhibit a peroxidase-like ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB). Au NBPs can be etched by the product, TMB2+, to form a significant longitudinal peak blue shift of local surface plasmon resonance. During the construction of the immunosensor, the microplate was coated with dopamine to immobilized OTA antigens, followed by the immunoreaction of OTA antibody and the Cu2O-labled secondary antibody. A linear relationship can be found between the local surface plasmon resonance (LSPR) peak changes with the logarithm of OTA concentration in a wide range from 1 ng/L to 5 µg/L, while the detection limit was 0.47 ng/L. Meanwhile, the approximate OTA concentration can be conveniently and intuitively observed by the vivid color changes. Benefiting from the high specificity, the proposed multi-colorimetric immunoassay detection of OTA in millet samples was achieved, indicating the available potential of the immunoassay for the determination of OTA in real samples.

Synthesis of Densely Immobilized Gold-Assembled Silica Nanostructures.

In this study, dense gold-assembled SiO2 nanostructure (SiO2@Au) was successfully developed using the Au seed-mediated growth. First, SiO2 (150 nm) was prepared, modified by amino groups, and incubated by gold nanoparticles (ca. 3 nm Au metal nanoparticles (NPs)) to immobilize Au NPs to SiO2 surface. Then, Au NPs were grown on the prepared SiO2@Au seed by reducing chloroauric acid (HAuCl4) by ascorbic acid (AA) in the presence of polyvinylpyrrolidone (PVP). The presence of bigger (ca. 20 nm) Au NPs on the SiO2 surface was confirmed by transmittance electronic microscopy (TEM) images, color changes to dark blue, and UV-vis spectra broadening in the range of 450 to 750 nm. The SiO2@Au nanostructure showed several advantages compared to the hydrofluoric acid (HF)-treated SiO2@Au, such as easy separation, surface modification stability by 11-mercaptopundecanoic acid (R-COOH), 11-mercapto-1-undecanol (R-OH), and 1-undecanethiol (R-CH3), and a better peroxidase-like catalysis activity for 5,5'-Tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) reaction. The catalytic activity of SiO2@Au was two times better than that of HF-treated SiO2@Au. When SiO2@Au nanostructure was used as a surface enhanced Raman scattering (SERS) substrate, the signal of 4-aminophenol (4-ATP) on the surface of SiO2@Au was also stronger than that of HF-treated SiO2@Au. This study provides a potential method for nanoparticle preparation which can be replaced for Au NPs in further research and development.

Synthesis of Finely Controllable Sizes of Au Nanoparticles on a Silica Template and Their Nanozyme Properties.

The precise synthesis of fine-sized nanoparticles is critical for realizing the advantages of nanoparticles for various applications. We developed a technique for preparing finely controllable sizes of gold nanoparticles (Au NPs) on a silica template, using the seed-mediated growth and interval dropping methods. These Au NPs, embedded on silica nanospheres (SiO2@Au NPs), possess peroxidase-like activity as nanozymes and have several advantages over other nanoparticle-based nanozymes. We confirmed their peroxidase activity; in addition, factors affecting the activity were investigated by varying the reaction conditions, such as concentrations of tetramethyl benzidine and H2O2, pH, particle amount, reaction time, and termination time. We found that SiO2@Au NPs are highly stable under long-term storage and reusable for five cycles. Our study, therefore, provides a novel method for controlling the properties of nanoparticles and for developing nanoparticle-based nanozymes.

Designing the Hotspots Distribution by Anisotropic Growth.

Changing the morphology of noble metal nanoparticles and polarization dependence of nanoparticles with different morphologies is an important part of further research on surface plasma enhancement. Therefore, we used the method based on Matlab simulation to provide a simple and effective method for preparing the morphologies of Au nanoparticles with different morphologies, and prepared the structure of Au nanoparticles with good uniformity and different morphologies by oblique angle deposition (OAD) technology. The change of the surface morphology of nanoparticles from spherical to square to diamond can be effectively controlled by changing the deposition angle. The finite difference time domain (FDTD) method was used to simulate the electromagnetic fields of Au nanoparticles with different morphologies to explore the polarization dependence of nanoparticles with different shapes, which was in good agreement with Raman spectrum.

A Comparative Study on the Oxidation of Label-Free Silver Triangular Nanoplates by Peroxides: Main Effects and Sensing Applications.

Nowadays, analytical systems based on silver triangular nanoplates (AgTNPs) have been shown as good prospects for chemical sensing. However, they still remain relatively poorly studied as colorimetric probes for sensing various classes of compounds. This study shows that these nanoparticles are capable of being oxidized by peroxides, including both hydrogen peroxide and its organic derivatives. The oxidation was found to result in a decrease in the AgTNPs' local surface plasmon resonance band intensity at 620 nm. This was proposed for peroxide-sensitive spectrophotometric determination. Five peroxides differing in their structure and number of functional groups were tested. Three of them easily oxidized AgTNPs. The effects of a structure of analytes and main exterior factors on the oxidation are discussed. The detection limits of peroxides in the selected conditions increased in the series peracetic acid < hydrogen peroxide < tert-butyl hydroperoxide, coming to 0.08, 1.6 and 24 µmol L-1, respectively. tert-Butyl peroxybenzoate and di-tert-butyl peroxide were found to have no effect on the spectral characteristics of AgTNPs. By the example of hydrogen peroxide, it was found that the determination does not interfere with 100-4000-fold quantities of common inorganic ions. The proposed approach was successfully applied to the analysis of drugs, cosmetics and model mixtures.

Laser-induced formation of Au/Pt nanorods with peroxidase mimicking and SERS enhancement properties for application to the colorimetric determination of H2O2.

Platinum nanoparticles (PtNPs) were uniformly grown on the surface of gold nanorods (AuNRs) by a laser irradiation procedure. Transmission electron microscopy confirmed that the PtNPs are uniformly grown on the surface of the AuNRs. The formation of PtNPs on the AuNRs leads to a red-shift of the absorption maximum from 734 nm to 766 nm. In addition, the efficiency of surface enhanced Raman scattering (SERS) is increased, but the photothermal conversion efficiency is decreased compared to pure AuNRs. The result indicates that electron transfer occurs between gold and platinum. The peroxidase mimicking effect of PtNPs, AuNRs and Au/Pt NRs by catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB; a quinone) in the presence of H2O2. The catalytic activity of Au/Pt NRs is higher than that of sole AuNRs or PtNPs by factors of 4.2 and 2.1, respectively. Thus, Au/Pt NRs have been used for the detection of peroxide and the limit of detection is 0.04 µM. This work provides an approach to integrate the peroxidase mimicking effect with SERS enhancement for potential application in detection. Graphical abstract A schematic diagram for the laser-induced growth of Au/Pt NRs and the colorimetric determination of hydrogen peroxide concentration with their peroxidase mimicking properties. The limit of detection is 0.04 µM based on the use of Au/Pt NRs as a catalyst.

Flexible Plasmonic Sensors.

Mechanical flexibility and the advent of scalable, low-cost, and high-throughput fabrication techniques have enabled numerous potential applications for plasmonic sensors. Sensitive and sophisticated biochemical measurements can now be performed through the use of flexible plasmonic sensors integrated into existing medical and industrial devices or sample collection units. More robust sensing schemes and practical techniques must be further investigated to fully realize the potentials of flexible plasmonics as a framework for designing low-cost, embedded and integrated sensors for medical, environmental, and industrial applications.

Actively Tunable "Single Peak/Broadband" Absorbent, Highly Sensitive Terahertz Smart Device Based on VO2.

In recent years, the development of terahertz (THz) technology has attracted significant attention. Various tunable devices for THz waves (0.1 THz-10 THz) have been proposed, including devices that modulate the amplitude, polarization, phase, and absorption. Traditional metal materials are often faced with the problem of non-adjustment, so the designed terahertz devices play a single role and do not have multiple uses, which greatly limits their development. As an excellent phase change material, VO2's properties can be transformed by external temperature stimulation, which provides new inspiration for the development of terahertz devices. To address these issues, this study innovatively combines metamaterials with phase change materials, leveraging their design flexibility and temperature-induced phase transition characteristics. We have designed a THz intelligent absorber that not only enables flexible switching between multiple functionalities but also achieves precise performance tuning through temperature stimulation. Furthermore, we have taken into consideration factors such as the polarization mode, environmental temperature, structural parameters, and incident angle, ensuring the device's process tolerance and environmental adaptability. Additionally, by exploiting the principle of localized surface plasmon resonance (LSPR) accompanied by local field enhancement, we have monitored and analyzed the resonant process through electric field characterization. In summary, the innovative approach and superior performance of this structure provide broader insights and methods for THz device design, contributing to its theoretical research value. Moreover, the proposed absorber holds potential for practical applications in electromagnetic invisibility, shielding, modulation, and detection scenarios.

Fabrication of heterogeneous bimetallic nanochains through photochemical welding for promoting the electrocatalytic hydrogen evolution reaction.

Heterogeneous bimetallic nanochains (NCs) have gained significant attention in the field of catalysis due to their abundant active sites, multi-component synergistic catalytic, and exotic electronic structures. Here, we present a novel approach to synthesize one-dimensional heterogeneous bimetallic nanochains using a local surface plasmon resonance (LSPR) based strategy of liquid-phase photochemical welding method containing self-assembly and subsequent welding processes. Initially, we introduce additives that facilitate the self-assembly and alignment of Au nanoparticles (NPs) into orderly lines. Subsequently, the LSPR effect of the Au NPs is stimulated by light, enabling the second metal precursor to overcome the energy barrier and undergo photodeposition in the gap between the arranged Au NPs, thereby connecting the nano-metal particles. This strategy can be extended to the photochemical welding of Au NPs-Ag and Au NRs. Using electrocatalytic hydrogen evolution reaction (HER) as a proof-of-concept application, the obtained one-dimensional structure of Au5Pt1 NCs exhibit promoted HER performances, where the mass activity of the Au5Pt1 nanochains is found to be 4.8 times higher than that of Au5Pt1 NPs and 10.4 times higher than that of commercial 20 wt% Pt/C catalysts. The promoted HER performance is benefited from the electron conduction ability and abundant active sites.

Construction of Ultrathin BiVO4-Au-Cu2O Nanosheets with Multiple Charge Transfer Paths for Effective Visible-Light-Driven Photocatalytic Degradation of Tetracycline.

In this study, unique BiVO4-Au-Cu2O nanosheets (NSs) are well designed and multiple charge transfer paths are consequently constructed. The X-ray photoelectron spectroscopy measurement during a light off-on-off cycle and redox capability tests of the photo-generated charge carriers confirmed the formation of Z-scheme heterojunction, which can facilitate the charge carrier separation and transfer and maintain the original strong redox potentials of the respective component in the heterojunction. The ultrathin 2D structure of the BiVO4 NSs provided sufficient surface area for the photocatalytic reaction. The local surface plasmon resonance (LSPR) effect of the electron mediator, Au NPs, enhanced the light absorption and promoted the excitation of hot electrons. The multiple charge transfer paths effectively promoted the separation and transfer of the charge carrier. The synergism of the abovementioned properties endowed the BiVO4-Au-Cu2O NSs with satisfactory photocatalytic activity in the degradation of tetracycline (Tc) with a removal rate of ≈80% within 30 min under visible light irradiation. The degradation products during the photocatalysis are confirmed by using ultra-high performance liquid chromatography-mass spectrometry and the plausible degradation pathways of Tc are consequently proposed. This work paves a strategy for developing highly efficient visible-light-driven photocatalysts with multiple charge transfer paths for removing organic contaminants in water.

A Novel Aptamer Biosensor Based on a Localized Surface Plasmon Resonance Sensing Chip for High-Sensitivity and Rapid Enrofloxacin Detection.

Enrofloxacin, a fluoroquinolone widely used in animal husbandry, presents environmental and human health hazards due to its stability and incomplete hydrolysis leading to residue accumulation. To address this concern, a highly sensitive aptamer biosensor utilizing a localized surface plasmon resonance (LSPR) sensing chip and microfluidic technology was developed for rapid enrofloxacin residue detection. AuNPs were prepared by the seed method and the AuNPs-Apt complexes were immobilized on the chip by the sulfhydryl groups modified on the end of the aptamer. The properties and morphologies of the sensing chip and AuNPs-Apt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, and scanning electron microscope (SEM), respectively. The sensing chip was able to detect enrofloxacin in the range of 0.01-100 ng/mL with good linearity, and the relationship between the response of the sensing chip and the concentration was Δλ (nm) = 1.288log ConENR (ng/mL) + 5.245 (R2 = 0.99), with the limit of detection being 0.001 ng/mL. The anti-interference, repeatability, and selectivity of this sensing chip were studied in detail. Compared with other sensors, this novel aptamer biosensor based on AuNPs-Apt complexes is expected to achieve simple, stable, and economical application in the field of enrofloxacin detection.

Biomimetic affinity sensor for the ultrasensitive detection of neonicotinoids.

Multiple pesticides are often used in combination to protect crops from pests. This makes rapid on-site detection of pesticide contamination challenging. Herein, we describe a method for simultaneous detection of diverse neonicotinoid pesticides using a sensor that combines neonicotinoid-specific odorant-binding protein 2 (OBP2), which was cloned from an insect chemical sensing protein and modified gold nanoparticles with local surface plasmon resonance (LSPR)-based digital nanoplasmonometry (DiNM). When neonicotinoid pesticides bind to OBP2 on gold nanoparticles, the induced LSPR shift peak wavelength is too small to be measured using conventional LSPR immunoassays. DiNM records and compares the scattered image intensity in two adjacent wavelength bands, A and B, centered on the LSPR peak. It considers both the peak shift and the relative intensity change in these two bands, resulting in a significant LSPR signal enhancement. Then the spectral-image contrast was computed as the signal response. Using this approach, we obtained excellent limits of detection (LODs) of 1.4, 1.5, and 4.5 ppb for the neonicotinoids imidacloprid, acetamiprid, and dinotefuran, respectively. Blind tests demonstrated high positive and negative rates for teas, approximately 85 and 100%, respectively. Recombinant OBP2 produced in E. coli offers several advantages over antibodies, including high yield, time savings, and cost effectiveness. Moreover, this method is highly selective and sensitive to neonicotinoids, making it practical for field use.

Plasmonic Nanomaterials in Dark Field Sensing Systems.

Plasma nanoparticles offer promise in data storage, biosensing, optical imaging, photoelectric integration, etc. This review highlights the local surface plasmon resonance (LSPR) excitation mechanism of plasmonic nanoprobes and its critical significance in the control of dark-field sensing, as well as three main sensing strategies based on plasmonic nanomaterial dielectric environment modification, electromagnetic coupling, and charge transfer. This review then describes the component materials of plasmonic nanoprobes based on gold, silver, and other noble metals, as well as their applications. According to this summary, researchers raised the LSPR performance of composite plasmonic nanomaterials by combining noble metals with other metals or oxides and using them in process analysis and quantitative detection.

Plasmonic Nanostructure Engineering with Shadow Growth.

Physical shadow growth is a vacuum deposition technique that permits a wide variety of 3D-shaped nanoparticles and structures to be fabricated from a large library of materials. Recent advances in the control of the shadow effect at the nanoscale expand the scope of nanomaterials from spherical nanoparticles to complex 3D shaped hybrid nanoparticles and structures. In particular, plasmonically active nanomaterials can be engineered in their shape and material composition so that they exhibit unique physical and chemical properties. Here, the recent progress in the development of shadow growth techniques to realize hybrid plasmonic nanomaterials is discussed. The review describes how fabrication permits the material response to be engineered and highlights novel functions. Potential fields of application with a focus on photonic devices, biomedical, and chiral spectroscopic applications are discussed.

Gold-semiconductor nanohybrids as advanced phototherapeutics.

Phototherapeutics is gaining momentum as a mainstream treatment for cancer, with gold-semiconductor nanocomposites showing promise as potent phototherapeutic agents due to their structural tunability, biocompatibility and functional diversity. Such nanohybrids possess plasmonic characteristics in the presence of gold and the catalytic nature of semiconductor units, as well as the unexpected physicochemical properties arising from the contact interface. This perspective provides an overview of the latest research on gold-semiconductor nanocomposites for photodynamic, photothermal and photocatalytic therapy. The relationship between the spatial configuration of these nanohybrids and their practical performance was explored to deliver comprehensive insights and guidance for the design and fabrication of novel composite nanoplatforms to enhance the efficiency of phototherapeutics, promoting the development of nanotechnology-based advanced biomedical applications.

Long Spiky Au-Ag Nanostar Based Fiber Probe for Surface Enhanced Raman Spectroscopy.

The detection performances of noble metal-based surface enhanced Raman spectroscopy (SERS) devices are determined by the compositions and geometries of the metal nanostructures, as well as the substrates. In the current study, long spiky Au-Ag alloy nanostars were synthesized, and both core diameters and spike lengths were controlled by Lauryl sulfobetaine concentrations (as the nanostructure growth skeleton). The long spiky star geometries were confirmed by transmission electron micrograph images. Elements energy dispersive spectrometer mapping confirmed that Au and Ag elements were inhomogeneously distributed in the nanostructures and demonstrated a higher Ag content at surface for potential better SERS performance. Selected synthesized spiky nanostars were uniformly assembled on multi-mode silica fiber for probe fabrication by silanization. The SERS performance were characterized using crystal violet (CV) and rhodamine 6G (R6G) as analyte molecules. The lowest detection limit could reach as low as 10-8 M, with a 6.23 × 106 enhancement factor, and the relationship between analyte concentrations and Raman intensities was linear for both CV and R6G, which indicated the potential qualitative and quantitative molecule detection applications. Moreover, the fiber probes also showed good reproducibility and stability in the ambient atmosphere.