Electromagnetic Field Enhancement Research Articles

3D Superstructures Consisting of Intersecting Gold Lamellae Formed by a Micelle‐Mediated Anisotropic Growth Approach

3D superstructures (3DSs) have attracted increasing interest because of the collective synergistic effects of individual building units, but their customization relies on tedious multistep strategy or high‐end nanofabrication technology. Herein, for the first time, a facile block copolymer micelle‐mediated anisotropic growth approach is reported to fabricate gold 3DSs consisting of tunable and intersecting lamellae with sawtooth‐like edges. The preparation of the 3DSs depends on the mediation of reduction kinetics of gold precursors and adsorption of block copolymer micelles on gold crystal surfaces using disulfiram as ligands. The thickness of lamellae in the 3DSs is controllable from ≈21 to 102 nm by adjusting the weight fraction of the micellar hydrophobicity blocks and the composed lamellar number is regulated from ≈3 to ≈30. Additional morphologies, such as a dendritic mesoporous structure and meatball‐like shapes, are obtained through controlling the extent of micelle swelling. Finite‐difference time‐domain simulations demonstrate that the unique 3DSs of gold lamellae with sawtooth‐like edges form abundant hotspots giving rise to surface‐enhanced Raman scattering (SERS). The 3DSs exhibit strong electromagnetic field enhancement and excellent performance as SERS substrates for detecting 4‐mercaptobenzoic acid.

Femtosecond laser-induced nanoparticle implantation into flexible substrate for sensitive and reusable microfluidics SERS detection

Surface-enhanced Raman spectroscopy (SERS) microfluidic system, which enables rapid detection of chemical and biological analytes, offers an effective platform to monitor various food contaminants and disease diagnoses. The efficacy of SERS microfluidic systems is greatly dependent on the sensitivity and reusability of SERS detection substrates to ensure repeated use for prolonged periods. This study proposed a novel process of femtosecond laser nanoparticle array (NPA) implantation to achieve homogeneous forward transfer of gold NPA on a flexible polymer film and accurately integrated it within microfluidic chips for SERS detection. The implanted Au-NPA strips show a remarkable electromagnetic field enhancement with the factor of 9 × 108 during SERS detection of malachite green (MG) solution, achieving a detection limit lower than 10 ppt, far better than most laser-prepared SERS substrates. Furthermore, Au-NPA strips show excellent reusability after several physical and chemical cleaning, because of the robust embedment of laser-implanted NPA in flexible substrates. To demonstrate the performance of Au-NPA, a SERS microfluidic system is built to monitor the online oxidation reaction between MG/NaClO reactants, which helps infer the reaction path. The proposed method of nanoparticle implantation is more effective than the direct laser structuring technique. It provides better performance for SERS detection, robustness of detection, and substrate flexibility and has a wider range of applications for microfluidic systems without any negative impact.

Open Cross-gap Gold Nanocubes with Strong, Large-Area, Symmetric Electromagnetic Field Enhancement for On-Particle Molecular-Fingerprint Raman Bioassays.

Plasmonic nanoparticles with an externally open nanogap can localize the electromagnetic (EM) field inside the gap and directly detect the target via the open nanogap with surface-enhanced Raman scattering (SERS). It would be beneficial to design and synthesize the open gap nanoprobes in a high yield for obtaining uniform and quantitative signals from randomly oriented nanoparticles and utilizing these particles for direct SERS analysis. Here, we report a facile strategy to synthesize open cross-gap (X-gap) nanocubes (OXNCs) with size- and EM field-tunable gaps in a high yield. The site-specific growth of Au budding structures at the corners of the AuNC using the principle that the Au deposition rate is faster than the surface diffusion rate of the adatoms allows for a uniform X-gap formation. The average SERS enhancement factor (EF) for the OXNCs with 2.6 nm X-gaps was 1.2 × 109, and the EFs were narrowly distributed within 1 order of magnitude for ∼93% of the measured OXNCs. OXNCs consistently displayed strong EM field enhancement on large particle surfaces for widely varying incident light polarization directions, and this can be attributed to the symmetric X-gap geometry and the availability of these gaps on all 6 faces of a cube. Finally, the OXNC probes with varying X-gap sizes have been utilized in directly detecting biomolecules with varying sizes without Raman dyes. The concept, synthetic method, and biosensing results shown here with OXNCs pave the way for designing, synthesizing, and utilizing plasmonic nanoparticles for selective, quantitative molecular-fingerprint Raman sensing and imaging applications.

Surface‐Enhanced Raman Scattering in BIC‐Driven Semiconductor Metasurfaces

AbstractSemiconductor‐based surface‐enhanced Raman spectroscopy (SERS) substrates, as a new frontier in the field of SERS, are hindered by their poor electromagnetic field confinement and weak light‐matter interaction. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, enable strong electromagnetic field enhancement and optical absorption engineering for a wide range of semiconductors. However, the engineering of semiconductor substrates into metasurfaces for improving SERS activity remains underexplored. Here, an improved SERS metasurface platform is developed that leverages the combination of titanium oxide (TiO2) and the emerging physical concept of optical bound states in the continuum (BICs) to boost the Raman emission. Moreover, fine‐tuning of BIC‐assisted resonant absorption offers a pathway for maximizing the photoinduced charge transfer effect (PICT) in SERS. High values of BIC‐assisted electric field enhancement (|E/E0|2 ≈103) are achieved, challenging the preconception of weak electromagnetic (EM) field enhancement on semiconductor SERS substrates. The BIC‐assisted TiO2 metasurface platform offers a new dimension in spectrally‐tunable SERS with earth‐abundant and bio‐compatible semiconductor materials, beyond the traditional plasmonic ones.

Self-Assembled Hyperbranched Gold Nanoarrays Decode Serum United Urine Metabolic Fingerprints for Kidney Tumor Diagnosis.

Serum united urine metabolic analysis comprehensively reveals the disease status for kidney diseases in particular. Thus, the precise and convenient acquisition of metabolic molecular information from united biofluids is vitally important for clinical disease diagnosis and biomarker discovery. Laser desorption/ionization mass spectrometry (LDI-MS) presents various advantages in metabolic analysis; however, there remain challenges in ionization efficiency and MS signal reproducibility. Herein, we constructed a self-assembled hyperbranched black gold nanoarray (HyBrAuNA) assisted LDI-MS platform to profile serum united urine metabolic fingerprints (S-UMFs) for diagnosis of early stage renal cell carcinoma (RCC). The closely packed HyBrAuNA afforded strong electromagnetic field enhancement and high photothermal conversion efficacy, enabling effective ionization of low abundant metabolites for S-UMF collection. With a uniform nanoarray, the platform presented excellent reproducibility to ensure the accuracy of S-UMFs obtained in seconds. When it was combined with automated machine learning analysis of S-UMFs, early stage RCC patients were discriminated from the healthy controls with an area under the curve (AUC) > 0.99. Furthermore, we screened out a panel of 9 metabolites (4 from serum and 5 from urine) and related pathways toward early stage kidney tumor. In view of its high-throughput, fast analytical speed, and low sample consumption, our platform possesses potential in metabolic profiling of united biofluids for disease diagnosis and pathogenic mechanism exploration.

Catalyst-On-Hotspot Nanoarchitecture: Plasmonic Focusing of Light onto Co-Photocatalyst for Efficient Light-To-Chemical Transformation.

Plasmon-mediated catalysis utilizing hybrid photocatalytic ensembles promises effective light-to-chemical transformation, but current approaches suffer from weak electromagnetic field enhancements from polycrystalline and isotropic plasmonic nanoparticles as well as poor utilization of precious co-catalyst. Here, efficient plasmon-mediated catalysis is achieved by introducing a unique catalyst-on-hotspot nanoarchitecture obtained through the strategic positioning of co-photocatalyst onto plasmonic hotspots to concentrate light energy directly at the point-of-reaction. Using environmental remediation as a proof-of-concept application, the catalyst-on-hotspot design (edge-AgOcta@Cu2 O) enhances photocatalytic advanced oxidation processes to achieve superior organic-pollutant degradation at ≈81% albeit having lesser Cu2 O co-photocatalyst than the fully deposited design (full-AgOcta@Cu2 O). Mass-normalized rate constants of edge-AgOcta@Cu2 O reveal up to 20-fold and 3-fold more efficient utilization of Cu2 O and Ag nanoparticles, respectively, compared to full-AgOcta@Cu2 O and standalone catalysts. Moreover, this design also exhibits catalytic performance >4-fold better than emerging hybrid photocatalytic platforms. Mechanistic studies unveil that the light-concentrating effect facilitated by the dense electromagnetic hotspots is crucial to promote the generation and utilization of energetic photocarriers for enhanced catalysis. By enabling the plasmonic focusing of light onto co-photocatalyst at the single-particle level, the unprecedented design offers valuable insights in enhancing light-driven chemical reactions and realizing efficient energy/catalyst utilizations for diverse chemical, environmental, and energy applications.

Tunable acoustic graphene plasmon enhanced nano-infrared spectroscopy

Nano-infrared spectroscopy (nano-IR) technology can surpass the diffraction limit of light, achieving infrared spectroscopic detection with a spatial resolution of ~ 10 nm, which is an important technical means for studying the chemical composition and structure of molecules at the nanoscale. However, the weak infrared absorption signals of nanoscale materials pose a significant challenge due to the large mismatch between their dimensions and the wavelength of infrared light. The infrared absorption signals of molecular vibrational modes are proportional to the square of the electromagnetic field intensity at their location, meaning that higher electromagnetic field intensity can significantly enhance molecular detection sensitivity. Acoustic graphene plasmons (AGP), excited by the interaction between free charges in graphene and image charges in metals, exhibit strong optical field localization and electromagnetic field enhancement. These properties make AGP an effective platform for enhancing nano-IR detection sensitivity. However, the fabrication of graphene nanostructures often introduces numerous edge defects due to the limitations of nanofabrication techniques, significantly reducing the electromagnetic field enhancement observed in experiments. Here, using finite element simulation, we theoretically propose a tunable enhanced nano-IR detection platform based on nanocavity-acoustic graphene plasmon (n-AGP), utilizing a graphene/air gap/gold nanocavity structure. This platform avoids the need for nanofabrication of graphene, thereby preventing defects and contamination introduced by processes such as electron beam exposure and plasma etching. By plotting the dispersion of n-AGP, we found that n-AGP has a high wavelength compression capability comparable to AGP (<i>λ</i><sub>0</sub>/<i>λ</i><sub>AGP</sub> = 48). Additionally, due to the introduction of the gold nanocavity structure, n-AGP possess an extremely small mode volume (<i>V</i><sub>n-AGP</sub> ≈ 10<sup>-7</sup><i>λ</i><sub>0</sub><sup>3</sup>, <i>λ</i><sub>0</sub> = 6.25 μm). By calculating the electric field intensity distribution (|<i>E</i><sub>norm</sub>|) and the normalized electric field intensity spectrum (i.e., the relationship between frequency and (|<i>E</i><sub>z</sub>|/|<i>E</i><sub>0</sub>|) of the n-AGP structure, it is evident that due to the high electron density on the gold surface, electromagnetic waves can reflect at the boundaries of the gold nanocavity and be resonantly enhanced within the nanocavity. At the resonant frequency of n-AGP (1800 cm<sup>-1</sup>), the electric field enhancement within the cavity is about 50 times. In contrast, at similar resonant frequencies, the electric field enhancement factors of Graphene plasmon (resonant frequency 1770 cm<sup>-1</sup>) and AGP (resonant frequency 1843 cm<sup>-1</sup>) are approximately 3 and 2 times, respectively, significantly lower than that of n-AGP. Furthermore, by placing a protein film (60 nm wide and 10 nm high) under the graphene, we calculated the spectral dip depths caused by Fano resonance between n-AGP and AGP with the vibrational modes of protein molecules, thereby validating the enhancement factors of different modes for protein vibrational mode infrared absorption. For the amide I band of proteins, the detection sensitivity of n-AGP is about 60 times higher than that of AGP. Additionally, we discovered that by adjusting the structural parameters of the gold nanocavity, including cavity depth, width, and surface roughness, the response frequency band of n-AGP can be modulated (from 1290 to 2124 cm<sup>-1</sup>). Specifically, as the cavity depth increases, the electric field enhancement of n-AGP improves, and the wavelength compression capability of n-AGP decreases, causing the resonant frequency to blue-shift (from 1793 cm<sup>-1</sup> to 2124 cm<sup>-1</sup>). As the cavity width increases, the resonant frequency of n-AGP red-shift (from 1793 cm<sup>-1</sup> to 1290 cm<sup>-1</sup>), and the effectiveness of the gold nanocavity boundary in reflecting the resonant electric field within the cavity diminishes, resulting in a decrease in the electric field enhancement factor. With the gradual increase in the roughness of the gold nanocavity bottom, the effective depth of the gold nanocavity increases, causing a blue shift in the n-AGP resonant frequency (from 1793 cm-1 to 1861 cm<sup>-1</sup>) and an increase in the electric field enhancement factor. Moreover, by adjusting the Fermi level of graphene (from 0.3 eV to 0.6 eV), we achieved dynamic tuning of n-AGP (from 1355 to 1973 cm<sup>-1</sup>). As the Fermi level of graphene increases, the wavelength compression capability of n-AGP decreases, resulting in a blue-shift in the resonant frequency. Finally, by optimizing the structural parameters and Fermi level of n-AGP, and placing protein particles of different sizes (20 nm, 15 nm, and 10 nm wide, all 10 nm high) into the graphene/gold nanocavity structure, we verified the protein detection capability of n-AGP-enhanced nano-IR. We found that n-AGP can detect the vibrational fingerprint features of the amide I and amide II bands of a single protein particle (10×10 nm) with a 15-fold increase in sensitivity. This n-AGP-based enhanced structure holds promise for providing an important detection platform for nanoscale material characterization and single-molecule detection, with broad application potential in biomedicine, materials science, and geology.

Plasma amplifiers: multiscale light-enhanced uniform SERS composite substrates for breaking through resonance limitations.

A phenomenon known as plasmon resonance constitutes a unique optical effect that can induce an enhancement in localized electromagnetic fields, resulting in a substantial increase in the electromagnetic field intensity surrounding metallic nanostructures. In this work, the coupling effect of excitation of surface plasmon polaritons and local surface plasmons in nanoparticles is deeply studied under the background of nanoparticles/one-dimension grating composite structures through grating matching. By employing finite-difference time-domain simulations as our methodological approach, we discern gratings with a periodicity of 1.5 μm support surface plasmon bound states between the gratings. Furthermore, the modulation of SPs along the vertical sidewalls of the grating due to standing wave effects exhibits oscillatory behavior with varying grating heights. Experimental results obtained from the nanoparticle/grating composite SERS substrate validate theoretical predictions, demonstrating higher enhanced Raman signals at 633 nm compared to 532 nm. Remarkably, this structure exhibits good performance, with R6G detection sensitivity down to concentrations as low as 10-10 M and mapping achieving a relative standard deviation of 7.79%, underscoring its uniformity and capability of electromagnetic field enhancement.

Controllable synthesis of multi-tip spatial gold nanostructures to facilitate SPR enhancement for exosomal PD-L1 assay

A surface plasmon resonance (SPR) biosensor was developed utilizing gold nanoflowers with multi-tip tiny petals (Au@Au mNFs) and multifunctional peptides for the selective detection of exosomal programmed cell death 1 ligand 1 (ExoPD-L1). In the presence of different salt concentrations, DNA-functionalized gold seeds underwent in situ gold growth, resulting in Au@Au NFs with varying numbers of petals or Au@Au nanospheres (Au@Au NSs). The growth orientation of the gold shells was influenced by the “upright”, “tilted” or “lying” state of the DNA on the gold core surface, depending on the salt concentration solution. The finally prepared Au@Au mNFs exhibited a multi-tip spatial structure, which served as a highly efficient SPR sensitized layer with abundant hot spots on the gold film surface. The enhanced SPR sensitivity was attributed to the substantial electromagnetic field enhancement generated at the tips of the mNFs. By achieving suitable surface coverage of the multifunctional peptide at the sensing interface constructed by Au@Au mNFs, efficient capture of ExoPD-L1 was ensured. The analysis results demonstrated that the developed SPR sensor successfully detected ExoPD-L1 within a concentration range of 10–107 particles/mL, with a detection limit of 4.95 particles/mL. This work highlights the significant improvement in SPR sensing and detection performance achieved by utilizing Au@Au mNFs with multi-tip spatial nanostructures, providing a straightforward approach for achieving ultra-sensitive detection of target substances through SPR.

Surface enhanced Raman scattering based on ZnO/Cu@Ag heterojunction for detecting γ-aminobutyric acid molecules

Detecting γ-aminobutyric acid (GABA) in the mammalian body is vital for diagnosing neurological disorders. Here, we introduced a novel SERS sensor based on metal-semiconductor heterojunction ZnO/Cu@Ag substrate for highly sensitive detecting GABA molecules. The ZnO/Cu@Ag substrate fully leverages the electromagnetic field enhancement effect and the chemical enhancement effect of metal-semiconductors heterojunction, exhibiting an excellent enhancement factor of 2.23 × 106 and a low limit-of-detection (LOD) of 3.84 nM for GABA molecules in water. Moreover, the ZnO/Cu@Ag substrate could recognize 10 nM GABA molecules in human serum. This GABA SERS sensor provides a reliable tool and technological support for research and applications in neuroscience and medicine.

Cascade amplification of optical absorption on III–V semiconductors via plasmon-coupled graphene

Plasmons in graphene (Gr) show many fascinating characteristics, such as dynamic tunability, strong field confinement of light-matter interaction, and highly responsive, which has been widely exploited for a number of applications, including photodetectors, optical modulators, and sensors. In this paper, graphene plasmons (GPs) were motivated by implanting Au nanoparticles (Au NPs) into Ta2O5 thin layers adjacent to the Gr film, and the strong localized surface plasmon resonance (LSPR) effect has been proposed and demonstrated by placing the GPs structure on a III–V semiconductor quantum well saturable absorber (SA). It has been substantiated that the heightened interaction between light and Gr via LSPR predominantly occurs through the mechanisms of resonant energy transfer and local electromagnetic field enhancement, rather than direct electron transfer. Significant improvement on the nonlinear characteristics of the GPs modulated III–V semiconductor SA has been observed with a 17.1% large modulation depth and obviously improved working stability. A 1550 nm passive mode-locked laser has been successfully constructed with a pulse width down to 523 fs by integrating the SA into the laser cavity. This work lays the foundation for the development of high-performance mode-locked lasers and also demonstrates the substantial enhancement of nonlinear optical properties of various materials not limited to III–V semiconductors provided by this GPs' modulated structure; hence, these findings offer extensive prospects for applications in various photonics and optoelectronic devices.

Plasmonic nanocavity-modulated electrochemiluminescence sensor for gastric cancer exosomal miRNA detection

Plasmonic nanocavity possessing highly light field confinement and electromagnetic field enhancement can concentrate and enhance the luminescence signal. The plasmonic nanocavity has the great potential value in biosensing research and improve analytical sensitivity. In this work, we constructed a plasmonic nanocavity between circular Au nanoplate-film and spherical Au nanoparticle with tetrahedral DNA nanostructures. The nanocavity structure can regulate the local density of optical states and provide the field restriction to enhance the spontaneous ECL radiation of PEDOT-S dots. Additionally, Au nanoparticle acted as nanoantenna which localized and modulated ECL to directional emission. Because the plasmonic nanocavity effectively collected and redistributed ECL signal, the emission was enhanced by 5.9 times with polarized characteristics. The proposed plasmonic nanocavity-based ECL sensor was further used to detect exosomal miRNA-223-3p in ascites. The detection results indicated the novel sensing strategy can assist early diagnosis of peritoneal metastasis of gastric cancer.

Spatial Distributions of Single-Molecule Reactivity in Plasmonic Catalysis.

Plasmonic catalysts have the potential to accelerate and control chemical reactions with light by exploiting localized surface plasmon resonances. However, the mechanisms governing plasmonic catalysis are not simple to decouple. Several plasmon-derived phenomena, such as electromagnetic field enhancements, temperature, or the generation of charge carriers, can affect the reactivity of the system. These effects are convoluted with the inherent (nonplasmonic) catalytic properties of the metal surface. Disentangling these coexisting effects is challenging but is the key to rationally controlling reaction pathways and enhancing reaction rates. This study utilizes super-resolution fluorescence microscopy to examine the mechanisms of plasmonic catalysis at the single-particle level. The reduction reaction of resazurin to resorufin in the presence of Au nanorods coated with a porous silica shell is investigated in situ. This allows the determination of reaction rates with a single-molecule sensitivity and subparticle resolution. By variation of the irradiation wavelength, it is possible to examine two different regimes: photoexcitation of the reactant molecules and photoexcitation of the nanoparticle's plasmon resonance. In addition, the measured spatial distribution of reactivity allows differentiation between superficial and far-field effects. Our results indicate that the reduction of resazurin can occur through more than one reaction pathway, being most efficient when the reactant is photoexcited and is in contact with the Au surface. In addition, it was found that the spatial distribution of enhancements varies, depending on the underlying mechanism. These findings contribute to the fundamental understanding of plasmonic catalysis and the rational design of future plasmonic nanocatalysts.

Tuning strong coupling towards the deep ultraviolet region realized through Tamm-plasmon exciton-polaritons

Light-matter interactions at the nanoscale have attracted considerable attention due to its features of high optical-field confinement and large electromagnetic-field enhancement. Herein, we theoretically demonstrate strong coupling between Tamm plasmon (TP) and exciton polaritons towards the deep ultraviolet (DUV) region in metal Al/distributed Bragg reflector (DBR)-molecular structures. By adjusting the thickness of the spacer layer and the angle of incident light, the obvious anti-crossing phenomena can be observed with a Rabi splitting of 38.4 meV. Moreover, through varying the period number of the DBR structure, the coupling strength can be effectively manipulated from weak to strong. These findings may extend the operating wavelength of strong coupling to the DUV region, and benefit the development of new-style optical filters.

Construction of SERS chip based on silver nanoparticles and detection of sports doping β-agonists

Sports doping is a persistent challenge in competitive sports, undermining the integrity of athletic competitions and posing health risks to athletes. This study focuses on the development of a surface-enhanced Raman spectroscopy (SERS) chip for the detection of β-agonists, such as clenbuterol, ractopamine, and salbutamol, which are commonly abused as performance-enhancing drugs. The SERS chip was constructed by depositing silver nanoparticles (AgNPs) onto activated carbon (AC) as a substrate, utilizing their plasmonic properties and ease of synthesis. The successful loading of AgNPs onto AC was confirmed by SEM imaging, demonstrating a uniform distribution of AgNPs on the surface of AC. The SERS chip exhibited enhanced sensitivity in detecting β-agonists compared to conventional methods. The SERS signals of the analytes decreased with decreasing concentrations, indicating the chip's ability to detect low-concentration analytes. Notably, the AC/AgNPs composite demonstrated stronger SERS signals compared to AgNPs alone, attributed to the improved loading efficiency and electromagnetic field enhancement provided by the AC substrate. The detection limit of the AC/AgNPs SERS chip for clenbuterol, ractopamine, and salbutamol was found to be 0.003 mg/L, 0.001 mg/L, and 0.007 mg/L, respectively. The developed SERS chip offers rapid and sensitive detection of β-agonists in sports doping control. It overcomes the limitations of conventional methods, such as immunoassays and chromatographic techniques, in terms of sensitivity, selectivity, and sample preparation time. The application of SERS in anti-doping efforts holds great promise for maintaining fair and clean sports competitions.

Tuning Catalytic Activity and Selectivity in Photocatalysis on Mie-Resonant Cuprous Oxide Particles: Distinguishing Electromagnetic Field Enhancement Effect from the Heating Effect

Tuning Catalytic Activity and Selectivity in Photocatalysis on Mie-Resonant Cuprous Oxide Particles: Distinguishing Electromagnetic Field Enhancement Effect from the Heating Effect

Dual-Plasmon Resonance Coupling Promoting Directional Photosynthesis of Nitrate from Air.

Photocatalysis, particularly plasmon-mediated photocatalysis, offers a green and sustainable approach for direct nitrogen oxidation into nitrate under ambient conditions. However, the unsatisfactory photocatalytic efficiency caused by the limited localized electromagnetic field enhancement and short hot carrier lifetime of traditional plasmonic catalysts is a stumbling block to the large-scale application of plasmon photocatalytic technology. Herein, we design and demonstrate the dual-plasmonic heterojunction (Bi/Csx WO3 ) achieves efficient and selective photocatalytic N2 oxidation. The yield of NO3 - over Bi/Csx WO3 (694.32 μg g-1 h-1 ) are 2.4 times that over Csx WO3 (292.12 μg g-1 h-1 ) under full-spectrum irradiation. The surface dual-plasmon resonance coupling effect generates a surge of localized electromagnetic field intensity to boost the formation efficiency and delay the self-thermalization of energetic hot carriers. Ultimately, electrons participate in the formation of ⋅O2 - , while holes involve in the generation of ⋅OH and the activation of N2 . The synergistic effect of multiple reactive oxygen species drives the direct photosynthesis of NO3 - , which achieves the overall-utilization of photoexcited electrons and holes in photocatalytic reaction. The concept that the dual-plasmon resonance coupling effect facilitates the directional overall-utilization of photoexcited carriers will pave a new way for the rational design of efficient photocatalytic systems.

Dual‐Plasmon Resonance Coupling Promoting Directional Photosynthesis of Nitrate from Air

AbstractPhotocatalysis, particularly plasmon‐mediated photocatalysis, offers a green and sustainable approach for direct nitrogen oxidation into nitrate under ambient conditions. However, the unsatisfactory photocatalytic efficiency caused by the limited localized electromagnetic field enhancement and short hot carrier lifetime of traditional plasmonic catalysts is a stumbling block to the large‐scale application of plasmon photocatalytic technology. Herein, we design and demonstrate the dual‐plasmonic heterojunction (Bi/CsxWO3) achieves efficient and selective photocatalytic N2 oxidation. The yield of NO3− over Bi/CsxWO3 (694.32 μg g−1 h−1) are 2.4 times that over CsxWO3 (292.12 μg g−1 h−1) under full‐spectrum irradiation. The surface dual‐plasmon resonance coupling effect generates a surge of localized electromagnetic field intensity to boost the formation efficiency and delay the self‐thermalization of energetic hot carriers. Ultimately, electrons participate in the formation of ⋅O2−, while holes involve in the generation of ⋅OH and the activation of N2. The synergistic effect of multiple reactive oxygen species drives the direct photosynthesis of NO3−, which achieves the overall‐utilization of photoexcited electrons and holes in photocatalytic reaction. The concept that the dual‐plasmon resonance coupling effect facilitates the directional overall‐utilization of photoexcited carriers will pave a new way for the rational design of efficient photocatalytic systems.

Delocalized Electric Field Enhancement through Near-Infrared Quasi-BIC Modes in a Hollow Cuboid Metasurface.

The two main problems of dielectric metasurfaces for sensing and spectroscopy based on electromagnetic field enhancement are that resonances are mainly localized inside the resonator volume and that experimental Q-factors are very limited. To address these issues, a novel dielectric metasurface supporting delocalized modes based on quasi-bound states in the continuum (quasi-BICs) is proposed and theoretically demonstrated. The metasurface comprises a periodic array of silicon hollow nanocuboids patterned on a glass substrate. The resonances stem from the excitation of symmetry-protected quasi-BIC modes, which are accessed by perturbing the arrangement of the nanocuboid holes. Thanks to the variation of the unit cell with a cluster of four hollow nanocuboids, polarization-insensitive, delocalized modes with ultra-high Q-factor are produced. In addition, the demonstrated electric field enhancements are very high (103-104). This work opens new research avenues in optical sensing and advanced spectroscopy, e.g., surface-enhanced Raman spectroscopy.

Superhydrophobic Surface Modification of Polymer Microneedles Enables Fabrication of Multimodal Surface-Enhanced Raman Spectroscopy and Mass Spectrometry Substrates for Synthetic Drug Detection in Blood Plasma.

Microneedles are widely used substrates for various chemical and biological sensing applications utilizing surface-enhanced Raman spectroscopy (SERS), which is indeed a highly sensitive and specific analytical approach. This article reports the fabrication of a nanoparticle (NP)-decorated microneedle substrate that is both a SERS substrate and a substrate-supported electrospray ionization (ssESI) mass spectrometry (MS) sample ionization platform. Polymeric ligand-functionalized gold nanorods (Au NRs) are adsorbed onto superhydrophobic surface-modified polydimethylsiloxane (PDMS) microneedles through the control of various interfacial interactions. We show that the chain length of the polymer ligands dictates the NR adsorption process. Importantly, assembling Au NRs onto the micrometer-diameter needle tips allows the formation of highly concentrated electromagnetic hot spots, which provide the SERS enhancement factor as high as 1.0 × 106. The micrometer-sized area of the microneedle top and high electromagnetic field enhancement of our system can be loosely compared with tip-enhanced Raman spectroscopy, where the apex of a plasmonic NP-functionalized sharp probe produces high-intensity plasmonic hot spots. Utilizing our NR-decorated microneedle substrates, the synthetic drugs fentanyl and alprazolam are analyzed with a subpicomolar limit of detection. Further analysis of drug-molecule interactions on the NR surface utilizing the Langmuir adsorption model suggests that the higher polarizability of fentanyl allows for a stronger interaction with hydrophilic polymer layers on the NR surface. We further demonstrate the translational aspect of the microneedle substrate for both SERS- and ssESI-MS-based detection of these two potent drugs in 10 drug-of-abuse (DOA) patient plasma samples with minimal preanalysis sample preparation steps. Chemometric analysis for the SERS-based detection shows a very good classification between fentanyl, alprazolam, or a mixture thereof in our selected 10 samples. Most importantly, ssESI-MS analysis also successfully identifies fentanyl or alprazolam in these same 10 DOA plasma samples. We believe that our multimodal detection approach presented herein is a highly versatile detection technology that can be applicable to the detection of any analyte type without performing any complicated sample preparation.