Plasmon-induced hot carrier science and technology

Coupling plasmon and catalytic-active hotspots of Au@Pt core-satellite nanoparticles for in-situ spectroscopic observation of plasmon-promoted decarboxylation

Plasmon-induced hot carriers are a promising "active" energy source, attracting increasing attention for their potential applications in photocatalysis and photodetection. Here, we hybridize plasmonic Au spherical nanoparticles (SNPs) with catalytically active Pt nanocrystals to form Au@Pt core-satellite nanoparticles (CSNPs), which act as both an efficient catalyst for plasmon-promoted decarboxylation reaction and a robust surface-enhanced Raman scattering (SERS) substrate for plasmon-enhanced molecular spectroscopic detection. By regulating the coverage of Pt nanocrystals on the Au SNPs, we modulated the "hotspot" structures of the Au@Pt CSNPs to optimize the SERS detecting capability and catalytic decarboxylation performance. The coupling functionalities enable us with unique opportunities to in-situ SERS monitor universal reactions catalyzed by active catalysts (e.g. Pt, Pd) in the chemical industry in real-time. The decarboxylation rate of 4-mercaptophenylacetic acid was dynamically controlled by the surface catalytic decarboxylation step, following first-order overall reaction kinetics. Moreover, the reaction rate exhibited a strong correlation with the local field enhancement |E/E0|4 of the hotspot structure. This work provides spectroscopic insights into the molecule-plasmon interface under the plasmon-promoted catalytic reactions, guiding the rational design of the plasmonic interface of nanocatalysts to achieve desired functionalities.

Amino acid-induced synthesis of chiral AgAuPt nanoparticles with branched structure for circularly polarized enantioselective photoelectrocatalytic water splitting

Chiral Plasmonic nanomaterials have gradually illustrated intriguing circularly polarized light (CPL)-dependent properties in photocatalysis due to their unique chiral optical activity. However, the connection between chiral characteristics and catalytic performance of these materials in cooperative systems is rarely reported and remains a challenge task. In this work, branched AgAuPt nanoparticles induced by L/d-cysteine (Cys) with strong and perfectly symmetric circular dichroism (CD) signals are synthesized. Chiral branched AgAuPt nanoparticles firstly exhibit superior typical electrocatalytic performance. In the photoelectrocatalytic system, chiral branched AgAuPt nanoparticles demonstrate selective catalytic water splitting performance. Specifically, chiral branched AgAuPt with related CPL irradiation exhibits enhanced acidic hydrogen evolution reaction (HER) performance. Under the continuous irradiation of related CPL, the chiral catalyst generates more heat, which further increases the catalytic activity. This contribution of heat is supported by density functional theory (DFT) calculation results. The changes in chiroptical activity during this process are recorded by variable temperature CD spectra. This work provides a novel paradigm for designing chiral catalysis systems and emphasizes the profound promise of chiral plasmonic nanomaterials as chiral catalysts.

Switching of electrochemical selectivity due to plasmonic field-induced dissociation

Electrochemical reactivity is known to be dictated by the structure and composition of the electrocatalyst-electrolyte interface. Here, we show that optically generated electric fields at this interface can influence electrochemical reactivity insofar as to completely switch reaction selectivity. We study an electrocatalyst composed of gold-copper alloy nanoparticles known to be active toward the reduction of CO2 to CO. However, under the action of highly localized electric fields generated by plasmonic excitation of the gold-copper alloy nanoparticles, water splitting becomes favored at the expense of CO2 reduction. Real-time time-dependent density functional tight binding calculations indicate that optically generated electric fields promote transient-hole-transfer-driven dissociation of the O─H bond of water preferentially over transient-electron-driven dissociation of the C─O bond of CO2. These results highlight the potential of optically generated electric fields for modulating pathways, switching reactivity on/off, and even directing outcomes.

Circularly Polarized Light-Induced Chiral Growth of Achiral Plasmonic Nanoparticles Dispersed in a Solution

Plasmonic nanoparticles (NPs) with chiral geometries have wide applications from chiral molecular sensing to enantioselective catalysis. The synthesis of chiral plasmonic nanoparticles using circularly polarized light (CPL) has attracted a considerable amount of attention because it eliminates the need for chiral molecules. However, NPs need to be immobilized on a solid substrate during synthesis. Here, we successfully synthesized colloidal chiral plasmonic NPs by depositing silver on the surface of achiral gold nanoparticles dispersed in a solution using CPL. Circular dichroism (CD) signals corresponding to the handedness of the irradiated CPL were observed when gold nanorods or gold nanotriangles were used. In contrast, no clear CD signal was observed when gold nanospheres were used. The morphological anisotropy of the gold nanoparticles was a key factor in the synthesis of chiral plasmonic nanoparticles using CPL. Furthermore, we demonstrated the tuning of chiroptical properties according to the CPL wavelength.

Titanium boride nanosheets with photo-enhanced sonodynamic efficiency for glioblastoma treatment

Sonodynamic therapy (SDT) has garnered significant attention in cancer treatment, however, the low-yield reactive oxygen species (ROS) generation from sonosensitizers remains a major challenge. In this study, titanium boride nanosheets (TiB2 NSs) with photo-enhanced sonodynamic efficiency was fabricated for SDT of glioblastoma (GBM). Compared with commonly-used TiO2 nanoparticles, the obtained TiB2 NSs exhibited much higher ROS generation efficiency under ultrasound (US) irradiation due to their narrower band gap (2.50 eV). Importantly, TiB2 NSs displayed strong localized surface plasmon resonance (LSPR) effect in the second near-infrared (NIR II) window, which facilitated charge transfer rate and improved the separation efficiency of US-triggered electron-hole pairs, leading to photo-enhanced ROS generation efficiency. Furthermore, TiB2 NSs were encapsulated with macrophage cell membranes (CM) and then modified with RGD peptide to construct biomimetic nanoagents (TiB2@CM-RGD) for efficient blood-brain barrier (BBB) penetrating and GBM targeting. After intravenous injection into the tumor-bearing mouse, TiB2@CM-RGD can efficiently cross BBB and accumulate in the tumor sites. The tumor growth was significantly inhibited under simultaneous NIR II laser and US irradiation without causing appreciable long-term toxicity. Our work highlighted a new type of multifunctional titanium-based sonosensitizer with photo-enhanced sonodynamic efficiency for GBM treatment. STATEMENT OF SIGNIFICANCE: Titanium boride nanosheets (TiB2 NSs) with photo-enhanced sonodynamic efficiency was fabricated for SDT of glioblastoma (GBM). The obtained TiB2 NSs displayed strong localized surface plasmon resonance (LSPR) effect in the second near-infrared (NIR II) window, which facilitated charge transfer rate and improved the separation efficiency of US-triggered electron-hole pairs, leading to photo-enhanced ROS generation efficiency. Furthermore, TiB2 NSs were encapsulated with macrophage cell membranes (CM) and then modified with RGD peptide to construct biomimetic nanoagents (TiB2@CM-RGD) for efficient blood-brain barrier (BBB) penetrating and GBM targeting. After intravenous injection into the tumor-bearing mouse, TiB2@CM-RGD can efficiently cross BBB and accumulate in the tumor sites. The tumor growth was significantly inhibited under simultaneous NIR II laser and US irradiation without causing appreciable long-term toxicity.

Plasmon-powered chemistry with visible-light active copper nanoparticles

In the quest for affordable materials for performing visible-light driven chemistry, we report here intriguing optical and photothermal properties of plasmonic copper nanoparticles (CuNPs). Precise tuning of reaction conditions and surface functionalization yield stable and monodisperse CuNPs, with a strong localized surface plasmon absorption at ∼580 nm. The molar extinction coefficient is estimated to be ∼7.7 × 107 M-1 cm-1 at 580 nm, which signifies their suitability for various light-harnessing studies. The characteristic wine-red colour and crystallography studies confirm the presence of mainly Cu(0) atoms in CuNPs, which showed excellent long-term colloidal and compositional stability under ambient conditions (at least 50 days). The as-synthesized oleylamine-capped CuNPs are ligand-exchanged with charged thiolate ligands of both polarities to form stable dispersions in water, with complete retention of their plasmonic properties and structural integrity (for ∼2 days and ∼6 h under inert and ambient conditions, respectively). Photothermal-conversion efficiency of CuNPs is estimated to be ∼80%, raising the surrounding temperature to ∼170 °C within ∼30 s of irradiation with a 1 W 532 nm diode laser, which is 'hot' enough to perform useful solar-vapor generation and high-temperature crystal-to-crystal phase transformation. Our work projects plasmonic CuNPs as an affordable and effective alternative to conventional metal NPs to harness light-matter interactions for future plasmon-powered chemistry.

Tailoring Plasmonic Nanoheaters Size for Enhanced Theranostic Agent Performance

The introduction of optimized nanoheaters, which function as theranostic agents integrating both diagnostic and therapeutic processes, holds significant promise in the medical field. Therefore, developing strategies for selecting and utilizing optimized plasmonic nanoheaters is crucial for the effective use of nanostructured biomedical agents. This work elucidates the use of the Joule number (Jo) as a figure of merit to identify high-performance plasmonic theranostic agents. A framework for optimizing metallic nanoparticles for heat generation was established, uncovering the size dependence of plasmonic nanoparticles optical heating. Gold nanospheres (AuNSs) with a diameter of 50 nm and gold nanorods (AuNRs) with dimensions of 41×10 nm were identified as effective nanoheaters for visible (530 nm) and infrared (808 nm) excitation. Notably, AuNRs achieve higher Jo values than AuNSs, even when accounting for the possible orientations of the nanorods. Theoretical results estimate that 41×10 nm gold nanorods have an average Joule number of 80, which is significantly higher compared to larger rods. The photothermal performance of optimal and suboptimal nanostructures was evaluated using photoacoustic imaging and photothermal therapy procedures. The photoacoustic images indicate that, despite having larger absorption cross-sections, the large nanoparticle volume of bigger particles leads to less efficient conversion of light into heat, which suggests that the use of optimized nanoparticles promotes higher contrast, benefiting photoacoustic-based procedures in diagnostic applications. The photothermal therapy procedure was performed on S180-bearing mice inoculated with 41×10 nm and 90×25 nm PEGylated AuNRs. Five minutes of laser irradiation of tumor tissue with 41×10 nm produced an approximately 9.5% greater temperature rise than using 90×25 AuNRs in the therapy trials. Optimizing metallic nanoparticles for heat generation may reduce the concentration of the nanoheaters used or decrease the light fluence for bioscience applications, paving the way for the development of more economical theranostic agents.

Air sampling and simultaneous detection of airborne influenza virus via gold nanorod-based plasmonic PCR

Reliable and sensitive virus detection is essential to prevent airborne virus transmission. The polymerase chain reaction (PCR) is one of the most compelling and effective diagnostic techniques for detecting airborne pathogens. However, most PCR diagnostics rely on thermocycling, which involves a time-consuming Peltier block heating methodology. Plasmonic PCR is based on light-driven photothermal heating of plasmonic nanostructures to address the key drawbacks of traditional PCR. This study introduces a methodology for plasmonic PCR detection of air-sampled influenza virus (H1N1). An electrostatic air sampler was used to collect the aerosolized virus in a carrier liquid for 10 min. Simultaneously, the viruses collected in the liquid were transferred to a tube containing gold (Au) nanorods (aspect ratio = 3.6). H1N1 viruses were detected in 12 min, which is the total time required for reverse transcription, fast thermocycling via plasmonic heating through gold nanorods, and in situ fluorescence detection. This methodology showed a limit of detection of three RNA copies/μL liquid for H1N1 influenza virus, which is comparable to that of commercially available PCR devices. This methodology can be used for the rapid and precise identification of pathogens on-site, while significantly reducing the time required for monitoring airborne viruses.

Magnetic nanoparticles and possible synergies with cold atmospheric plasma for cancer treatment

The biomedical applications of magnetic nanoparticles (MNPs) have gained increasing attention due to their unique biological, chemical, and magnetic properties such as biocompatibility, chemical stability, and high magnetic susceptibility. However, several critical issues still remain that have significantly halted the clinical translation of these nanomaterials such as the relatively low therapeutic efficacy, hyperthermia resistance, and biosafety concerns. To identify innovative approaches possibly creating synergies with MNPs to resolve or mitigate these problems, we delineated the anti-cancer properties of MNPs and their existing onco-therapeutic portfolios, based on which we proposed cold atmospheric plasma (CAP) to be a possible synergizer of MNPs by enhancing free radical generation, reducing hyperthermia resistance, preventing MNP aggregation, and functioning as an innovative magnetic and light source for magnetothermal- and photo-therapies. Our insights on the possible facilitating role of CAP in translating MNPs for biomedical use may inspire fresh research directions that, once actualized, gain mutual benefits from both.

The paradox of thermal vs. non-thermal effects in plasmonic photocatalysis

The debate surrounding the roles of thermal and non-thermal pathways in plasmonic catalysis has captured the attention of researchers and sparked vibrant discussions within the scientific community. In this review, we embark on a thorough exploration of this intriguing discourse, starting from fundamental principles and culminating in a detailed understanding of the divergent viewpoints. We probe into the core of the debate by elucidating the behavior of excited charge carriers in illuminated plasmonic nanostructures, which serves as the foundation for the two opposing schools of thought. We present the key arguments and evidence put forth by proponents of both the non-thermal and thermal pathways, providing a perspective on their respective positions. Beyond the theoretical divide, we discussed the evolving methodologies used to unravel these mechanisms. We discuss the use of Arrhenius equations and their variations, shedding light on the ensuing debates about their applicability. Our review emphasizes the significance of localized surface plasmon resonance (LSPR), investigating its role in collective charge oscillations and the decay dynamics that influence catalytic processes. We also talked about the nuances of activation energy, exploring its relationship with the nonlinearity of temperature and light intensity dependence on reaction rates. Additionally, we address the intricacies of catalyst surface temperature measurements and their implications in understanding light-triggered reaction dynamics. The review further discusses wavelength-dependent reaction rates, kinetic isotope effects, and competitive electron transfer reactions, offering an all-inclusive view of the field. This review not only maps the current landscape of plasmonic photocatalysis but also facilitates future explorations and innovations to unlock the full potential of plasmon-mediated catalysis, where synergistic approaches could lead to different vistas in chemical transformations.

Photo-Thermal Conversion and Raman Sensing Properties of Three-Dimensional Gold Nanostructure

Three-dimensional plasma nanostructures with high light-thermal conversion efficiency show the prospect of industrialization in various fields and have become a research hotspot in areas of light-heat utilization, solar energy capture, and so on. In this paper, a simple chemical synthesis method is proposed to prepare gold nanoparticles, and the electrophoretic deposition method is used to assemble large-area three-dimensional gold nanostructures (3D-GNSs). The light-thermal water evaporation monitoring and surface-enhanced Raman scattering (SERS) measurements of 3D-GNSs were performed via theoretical simulation and experiments. We reveal the physical processes of local electric field optical enhancement and the light-thermal conversion of 3D-GNSs. The results show that with the help of the efficient optical trapping and super-hydrophilic surface properties of 3D-GNSs, they have a significant effect in accelerating water evaporation, which was increased by nearly eight times. At the same time, the three-dimensional SERS substrates based on gold nanosphere particles (GNSPs) and gold nanostar particles (GNSTs) had limited sensitivities of 10-10 M and 10-12 M to R6G molecules, respectively. Therefore, 3D-GNSs show strong competitiveness in the fields of solar-energy-induced water purification and the Raman trace detection of organic molecules.

Unveiling the Mechanism of Plasmon Photocatalysis via Multiquantum Vibrational Excitation

Plasmon photocatalysis reactions are thought to occur through vibrationally activated reactants, driven by nonthermal energy transfer from plasmon-induced hot carriers. However, a detailed quantum-state-level understanding and quantification of the activation have been lacking. Using anti-Stokes surface-enhanced Raman scattering (SERS) spectroscopy, we mapped the vibrational population distributions of reactants on plasmon-excited nanostructures. Our results reveal a highly nonthermal distribution with an anomalously enhanced population of multiquantum excited states  (v ≥ 2). The shape of the distribution and its dependence on local field intensity and excitation wavelength cannot be explained by photothermal heating or vibronic optical transitions of the metal-molecule complex. Instead, it can be modeled by hot electron-molecule energy transfer mediated by the transient negative ions, establishing direct links among nonthermal reactant activation, plasmon-induced hot electrons, and negative ion resonances. Moreover, the presence of multiquantum excited reactants, which are far more reactive than those in the ground state or first excited state, presents opportunities for vibrationally controlling chemical selectivities.

Bimetallic FeCo-MOFs mediated Au nanorods etching for the multi-colorimetric and photothermal immunosensing of illegal additive

With the rapid expansion of the health food industry, the scope of safety supervision has also increased. However, traditional instrument detection methods cannot meet the requirements for the rapid on-site detection. Hence, the development of a rapid, precise, and simple method for the analysis of illegal additives in health foods is of great importance. In this work, by using FeCo-MOFs as mimetic peroxidase to mediate Au nanorods (Au NRs) etching, a dual-mode immunosensor based on multi-colorimetric and photothermal signals was fabricated to detect furosemide (FUR). In multi-colorimetric channel, the localized surface plasmon resonance (LSPR) peaks of Au NRs shifted blue, resulting in multi-color changes from red to gray to blue and finally to purple. In photothermal channel, the photothermal effect of Au NRs decreased, resulting in temperature changes. In the range of 1.0 × 10-5-1.0 × 10-2 μg/mL, both LSPR peak blue shift and temperature changes were linearly correlated with the logarithm of FUR concentration, with the detection limits were 4.9 × 10-6 and 8.5 × 10-6 μg/mL, respectively. Furthermore, its concentration can be accurately and intuitively assessed through the observation of vivid colorimetric changes. This advancement offers a highly promising approach for the on-site detection of FUR, facilitating timely and efficient monitoring, thereby significantly enhancing regulatory compliance and ensuring consumer safety.

Diffusion Behaviors of CaCl2-NaCl Molten Salt under an Electric Field: A Deep Potential Molecular Dynamics Simulation

CaCl2-NaCl molten salt is one of the widely used electrolytes, and the effect of the electric field on it needs to be considered in the environment of manufacturing metals and alloys as well as in battery applications. To be closer to the state of the CaCl2-NaCl molten salt system in practical applications, this study uses the training-based deep potential, combined with the ionic structure, to analyze the electric field effects on the drift velocity, ionic mobility, ion diffusion, and viscosity of the CaCl2-NaCl system by molecular dynamics simulations. It is shown that the electric field has a stronger effect on the ion diffusion behavior parallel to the direction of the electric field in the CaCl2-NaCl molten salt system. Due to the looser coordinate structure of Na+, the interaction force between Na-Cl is small compared with that between Ca-Cl. Na+ is easily driven and more sensitive to the electric field, whose drift velocity, ionic mobility, and diffusion coefficient are larger than those of the other two ions, with an order of Na+ > Cl- > Ca2+. All ionic drift velocities increase linearly as electric field intensity increases and the ionic mobilities tend to be constant. The diffusion coefficient parallel to the direction of the electric field exponentially increases and the viscosity tends to exponentially decrease with the increase in the electric field intensity. This work is important for accurately predicting the properties and performance of molten salts and their improvement for applications such as solar thermal energy conversion.

Superhydrophobic Solar-to-Thermal Materials Toward Cutting-Edge Applications

Solar-to-thermal conversion is a direct and effective way to absorb sunlight for heat via the rational design and control of photothermal materials. However, when exposed to water-existed conditions, the conventional solar-to-thermal performance may experience severe degradation owing to the high specific heat capacity of water. To tackle with the challenge, the water-repellent function is introduced to construct superhydrophobic solar-to-thermal materials (SSTMs) for achieving stable heating, and even, for creating new application possibilities under water droplets, sweat, seawater, and ice environments. An in-depth review of cutting-edge research of SSTMs is given, focusing on synergetic functions, typical construction methods, and cutting-edge potentials based on water medium. Moreover, the current challenges and future prospects based on SSTMs are also carefully discussed.

Hot Electron Cooling in n-Doped Colloidal Nanoplatelets Following Near-Infrared Intersubband Excitation

Intersubband transition was recently discovered in colloidal nanoplatelets, but the associated intersubband carrier relaxation dynamics remains poorly understood. In particular, it is crucial to selectively excite the intersubband transition and to follow the hot electron dynamics in the absence of valence-band holes. This is achieved herein by exciting the predoped electrons in CdSe/ZnS nanoplatelets using near-infrared femtosecond pulses and monitoring nonequilibrium electron dynamics using broad-band visible pulses. We find that the n = 2 electrons relax to the n = 1 subband and establish a Fermi-Dirac distribution within 200 fs, and finally reach an equilibrium with the lattice within a few ps. The cooling dynamics depend mainly on the excitation fluence but weakly on the doping density and the lattice temperature. These characteristics are well captured by our numerical simulation that explicitly accounts for the state occupation effect and optical phonon scattering.

Nanoplasmonic biosensors for environmental sustainability and human health

Monitoring the health conditions of the environment and humans is essential for ensuring human well-being, promoting global health, and achieving sustainability. Innovative biosensors are crucial in accurately monitoring health conditions, uncovering the hidden connections between the environment and human well-being, and understanding how environmental factors trigger autoimmune diseases, neurodegenerative diseases, and infectious diseases. This review evaluates the use of nanoplasmonic biosensors that can monitor environmental health and human diseases according to target analytes of different sizes and scales, providing valuable insights for preventive medicine. We begin by explaining the fundamental principles and mechanisms of nanoplasmonic biosensors. We investigate the potential of nanoplasmonic techniques for detecting various biological molecules, extracellular vesicles (EVs), pathogens, and cells. We also explore the possibility of wearable nanoplasmonic biosensors to monitor the physiological network and healthy connectivity of humans, animals, plants, and organisms. This review will guide the design of next-generation nanoplasmonic biosensors to advance sustainable global healthcare for humans, the environment, and the planet.

Electronic Structure and Functions of Carbon Nitride in Frontier Green Catalysis

ConspectusGraphitic carbon nitride-based materials have emerged as promising photocatalysts for a variety of energy and environmental applications owing to their "earth-abundant" nature, structural versatility, tunable electronic and optical properties, and chemical stability. Optimizing carbon nitride's physicochemical properties encompasses a variety of approaches, including the regulation of inherent structural defects, morphology control, heterostructure construction, and heteroatom and metal-atom doping. These strategies are pivotal in ultimately enhancing their photocatalytic activities. Previous reviews with extensive examples have mainly focused on the synthesis, modification, and application of carbon nitride-based materials in photocatalysis. However, there has been a lack of straightforward and in-depth discussion to understand the electronic characteristics and functions of various engineered carbon nitrides as well as their precise tailoring strategies and ultimately to explain the regularity and specificity of their improved performance in targeted photocatalytic systems. In the past ten years, our group has conducted extensive investigations on carbon nitride-based materials and their application in photocatalysis. These studies demonstrate the close yet intricate relationship between the electronic structure of carbon nitride materials and their photocatalytic reactivity. Understanding the electronic structure and functions of carbon nitride, as well as different engineering strategies, is essential for the improvement of photocatalytic processes from fundamental study to practical applications.To this end, in this Account, we first delve into the nature of the electronic properties of carbon nitride, highlighting the electronic structures, including band structure, density of states, molecular orbitals, and band center, as well as its electronic functions, such as the charge distribution, internal electric field, and external electric force. Subsequently, based on recent research in our group, we present a detailed discussion of the strategic modifications of carbon nitride and the consequential impacts on the physicochemical properties, particularly the optical properties and intrinsic electronic characteristics, for enhancing the photocatalytic performance. These modifications are categorized as follows: (i) component changing, which involves intralayer and interface heterojunctions as well as homojunctions, to modulate the band-edge potentials and reactivity of photoinduced electrons and holes toward surface redox reactions; (ii) dimensional tuning, which engineers the dimensional structure of carbon nitride, to influence the electron transfer direction; (iii) defect and heteroatom modification, which introduces a symmetry break in the carbon nitride framework, to promote charge redistribution for altering the charge density and electronic structure; and (iv) anchoring of single-atom metals to facilitate orbital hybridization and charge transfer enhancement through the unique metal-N coordination configurations. Finally, we propose an appraisal of the prospects and challenges in the precise manipulation and characterization of the electronic structure and functions of carbon nitride. The integration of in situ electronic structure analysis, theoretical calculation based on machine learning, and precise mechanism study may propel its substantial development in the light-driven circular economy. We hope this Account aspires to offer novel insights and perspectives into the operational mechanisms and tailored structure of carbon nitride-based materials in photocatalysis.

Assessing plasmon-induced reactions by a combined quantum chemical-quantum/classical hybrid approach

Plasmon-driven reactions on metal nanoparticles feature rich and complex mechanistic contributions, involving a manifold of electronic states, near-field enhancement, and heat, among others. Although localized surface plasmon resonances are believed to initiate these reactions, the complex reactivity demands deeper exploration. This computational study investigates factors influencing chemical processes on plasmonic nanoparticles, exemplified by protonation of 4-mercaptopyridine (4-MPY) on silver nanoparticles. We examine the impact of molecular binding modes and molecule-molecule interactions on the nanoparticle's surface, near-field electromagnetic effects, and charge-transfer phenomena. Two proton sources were considered at ambient conditions, molecular hydrogen and water. Our findings reveal that the substrate's binding mode significantly affects not only the energy barriers governing the thermodynamics and kinetics of the reaction but also determine the directionality of light-driven charge-transfer at the 4-MPY-Ag interface, pivotal in the chemical contribution involved in the reaction mechanism. In addition, significant field enhancement surrounding the adsorbed molecule is observed (eletromagnetic contribution) which was found insufficient to modify the ground state thermodynamics. Instead, it initiates and amplifies light-driven charge-transfer and thus modulates the excited states' reactivity in the plasmonic-molecular hybrid system. This research elucidates protonation mechanisms on silver surfaces, highlighting the role of molecular-surface and molecule-molecule-surface orientation in plasmon-catalysis.

Visible light enhanced catalytic activity of Aun subnanoclusters: the importance of d-sp interband transitions

Polymers can serve as an effective matrix to stabilize gold nanoparticles. These materials offer a continuous light-activated supply of subnanoclusters, which are composed of a few atoms. We report an efficient approach to enhance the catalytic activity of gold subnanoclusters by in situ feeding of these species through the generation of hot carriers via 5d-6s6p interband transitions on PEG-stabilized Au nanoparticles.

Advanced Anti-Icing Strategies and Technologies by Macrostructured Photothermal Storage Superhydrophobic Surfaces

Water is the source of life and civilization, but water icing causes catastrophic damage to human life and diverse industrial processes. Currently, superhydrophobic surfaces (inspired by the lotus effect) aided anti-icing attracts intensive attention due to their energy-free property. Here, recent advances in anti-icing by design and functionalization of superhydrophobic surfaces are reviewed. The mechanisms and advantages of conventional, macrostructured, and photothermal superhydrophobic surfaces are introduced in turn. Conventional superhydrophobic surfaces, as well as macrostructured ones, easily lose the icephobic property under extreme conditions, while photothermal superhydrophobic surfaces strongly rely on solar illumination. To address the above issues, a potentially smart strategy is found by developing macrostructured photothermal storage superhydrophobic (MPSS) surfaces, which integrate the functions of macrostructured superhydrophobic materials, photothermal materials, and phase change materials (PCMs), and are expected to achieve all-day anti-icing in various fields. Finally, the latest achievements in developing MPSS surfaces, showcasing their immense potential, are highlighted. Besides, the perspectives on the future development of MPSS surfaces are provided and the problems that need to be solved in their practical applications are proposed.

Dynamical Janus-Like Behavior Excited by Passive Cold-Heat Modulation in the Earth-Sun/Universe System: Opportunities and Challenges

The utilization of solar-thermal energy and universal cold energy has led to many innovative designs that achieve effective temperature regulation in different application scenarios. Numerous studies on passive solar heating and radiation cooling often operate independently (or actively control the conversion) and lack a cohesive framework for deep connections. This work provides a concise overview of the recent breakthroughs in solar heating and radiation cooling by employing a mechanism material in the application model. Furthermore, the utilization of dynamic Janus-like behavior serves as a novel nexus to elucidate the relationship between solar heating and radiation cooling, allowing for the analysis of dynamic conversion strategies across various applications. Additionally, special discussions are provided to address specific requirements in diverse applications, such as optimizing light transmission for clothing or window glass. Finally, the challenges and opportunities associated with the development of solar heating and radiation cooling applications are underscored, which hold immense potential for substantial carbon emission reduction and environmental preservation. This work aims to ignite interest and lay a solid foundation for researchers to conduct in-depth studies on effective and self-adaptive regulation of cooling and heating.

Pulsed Photothermal Therapy of Solid Tumors as a Precondition for Immunotherapy

Photothermal therapy (PTT) refers to the use of plasmonic nanoparticles to convert electromagnetic radiation in the near infrared region to heat and kill tumor cells. Continuous wave lasers have been used clinically to induce PTT, but the treatment is associated with heat-induced tissue damage that limits usability. Here, the engineering and validation of a novel long-pulsed laser device able to induce selective and localized mild hyperthermia in tumors while reducing the heat affected zone and unwanted damage to surrounding tissue are reported. Long-pulsed PTT induces acute necrotic cell death in heat affected areas and the release of tumor associated antigens. This antigen release triggers maturation and stimulation of CD80/CD86 in dendritic cells in vivo that primes a cytotoxic T cell response. Accordingly, long-pulsed PTT enhances the therapeutic effects of immune checkpoint inhibition and increases survival of mice with bladder cancer. Combined, the data promote long-pulsed PTT as a safe and effective strategy for enhancing therapeutic responses to immune checkpoint inhibitors while minimizing unwanted tissue damage.

Plasmon-Induced Hot Electrons in Nanostructured Materials: Generation, Collection, and Application to Photochemistry

Plasmon refers to the coherent oscillation of all conduction-band electrons in a nanostructure made of a metal or a heavily doped semiconductor. Upon excitation, the plasmon can decay through different channels, including nonradiative Landau damping for the generation of plasmon-induced energetic carriers, the so-called hot electrons and holes. The energetic carriers can be collected by transferring to a functional material situated next to the plasmonic component in a hybrid configuration to facilitate a range of photochemical processes for energy or chemical conversion. This article centers on the recent advancement in generating and utilizing plasmon-induced hot electrons in a rich variety of hybrid nanostructures. After a brief introduction to the fundamentals of hot-electron generation and decay in plasmonic nanocrystals, we extensively discuss how to collect the hot electrons with various types of functional materials. With a focus on plasmonic nanocrystals made of metals, we also briefly examine those based upon heavily doped semiconductors. Finally, we illustrate how site-selected growth can be leveraged for the rational fabrication of different types of hybrid nanostructures, with an emphasis on the parameters that can be experimentally controlled to tailor the properties for various applications.

Optimized Photothermal Conversion Ability through Interband Transitions in FeCoNiCrMn High-Entropy-Alloy Nanoparticles

High-entropy-alloy nanoparticles (HEA-NPs) composed of 3d transition metallic elements have attracted intensive attention in photothermal conversion regions due to their d-d interband transitions (IBTs). However, the effect arising from the unbalanced elemental ratio still needs more focus. In this work, FeCoNiCrMn HEA-NPs with different elemental ratios among Cr and Mn have been employed to clarify the impact of different composed elements on the optical absorption and photothermal conversion performance. It can be recognized that the unbalanced elemental ratio of HEA-NPs can reduce the photothermal performance. Density functional theory calculation demonstrated that d-d IBTs can be changed by the different composed element ratios, resulting in a number of insufficient filling regions around the Fermi level (±4 eV). As a result, the HEA-NPs (FeCoNiCr0.75Mn0.25) with a balanced elemental ratio exhibit the highest surface temperature of 97.6 °C under 1 sun irradiation, and the evaporation rate and energy conversion efficiency could reach 2.13 kg·m-2·h-1 and 93%, respectively, demonstrating effective solar steam generation behavior.

Mass Transport Limitations in Plasmonic Photocatalysis

The interpretation of mechanisms governing hot carrier reactivity on metallic nanostructures is critical, yet elusive, for advancing plasmonic photocatalysis. In this work, we explored the influence of the diffusion of molecules on the hot carrier extraction rate at the solid-liquid interface, which is of fundamental interest for increasing the efficiency of photodevices. Through a spatially defined scanning photoelectrochemical microscopy investigation, we identified a diffusion-controlled regime hindering the plasmon-driven photochemical activity of metallic nanostructures. Using low-power monochromatic illumination (<2 W cm-2), we unveiled the hidden influence of mass transport on the quantum efficiency of plasmonic photocatalysts. The availability of molecules at the solid-liquid interface directly limits the extraction of hot holes, according to their nature and energy, at the reactive spots in Au nanoislands on an ultrathin TiO2 substrate. An intriguing question arises: does the mass transport enhancement caused by thermal effects unlock the reactivity of nonthermal carriers under steady state?

High-Efficiency Photothermal Water Evaporation under Low-Intensity Sunlight Using Wood Biochar Monolith

Utilizing energy directly from the sun, solar water evaporation drives the global hydrological cycle and produces freshwater from saline water in the oceans and on land. As water is a poor solar absorber, a photothermal material is needed to facilitate the conversion of photons to thermal energy and increase the efficiency of solar desalination. However, the current photothermal materials are less efficient and expensive to be manufactured. Inspired by nature, we created a new photothermal material called a wood biochar monolith (WBM) by carbonizing wood using the pyrolysis process at 1000 °C and subsequently steaming at high pressure. Under low light intensity (193 W/m2), the light to vapor efficiency of maple WBM is more than 100%. The outstanding performance of WBM is attributed to (1) the facilitated water transport in the hierarchical, open-pore network preserved from the wood precursor in WBM and (2) the reduced evaporation enthalpy of confined water in WBM and the high broadband sunlight absorptivity of WBM. Moreover, the high evaporation rate causes the temperature of WBM to be lower than that of the surrounding water, enabling thermal energy harvesting by WBM from water and making a light-to-vapor efficiency of >100% feasible. This discovery offers opportunities for developing low-cost, high-performance water desalination or humidification devices deployable in remote areas with nonconcentrated natural sunlight.

Hot Electrons in a Steady State: Interband vs Intraband Excitation of Plasmonic Gold

Understanding the dynamics of "hot", highly energetic electrons resulting from nonradiative plasmon decay is crucial for optimizing applications in photocatalysis and energy conversion. This study presents an analysis of electron kinetics within plasmonic metals, focusing on the steady-state behavior during continuous-wave (CW) illumination. Using an inelastic spectroscopy technique, we quantify the temperature and lifetimes of distinct carrier populations during excitation. A significant finding is the monotonic increase in hot electron lifetime with decreases in electronic temperature. We also observe a 1.22× increase in hot electron temperature during intraband excitation compared to interband excitation and a corresponding 2.34× increase in carrier lifetime. The shorter lifetimes during interband excitation are hypothesized to result from direct recombination of nonthermal holes and hot electrons, highlighting steady-state kinetics. Our results help bridge the knowledge gap between ultrafast and steady-state spectroscopies, offering critical insights for optimizing plasmonic applications.

Quantifying Ultrafast Energy Transfer from Plasmonic Hot Carriers for Pulsed Photocatalysis on Nanostructures

Photocatalysis with plasmonic nanostructures has lately emerged as a transformative paradigm to drive and alter chemical reactions using light. At the surface of metallic nanoparticles, photoexcitation results in strong near fields, short-lived high-energy "hot" carriers, and light-induced heating, thus creating a local environment where reactions can occur with enhanced efficiencies. In this context, it is critical to understand how to manipulate the nonequilibrium processes triggered by light, as their ultrafast (femto- to picoseconds) relaxation dynamics compete with the process of energy transfer toward the reactants. Accurate predictions of the plasmon photocatalytic activity can lead to optimized nanophotonic architectures with enhanced selectivity and rates, operating beyond the intrinsic limitations of the steady state. Here, we report on an original modeling approach to quantify, with space, time, and energy resolution, the ultrafast energy exchange from plasmonic hot carriers (HCs) to molecular systems adsorbed on the metal nanoparticle surface while consistently accounting for photothermal bond activation. Our analysis, illustrated for a few typical cases, reveals that the most energetic nonequilibrium carriers (i.e., with energies well far from the Fermi level) may introduce a wavelength-dependence of the reaction rates, and it elucidates on the role of the carriers closer to the Fermi energy and the photothermally heated lattice, suggesting ways to enhance and optimize each contribution. We show that the overall reaction rates can benefit strongly from using pulsed illumination with the optimal pulse width determined by the properties of the system. Taken together, these results contribute to the rational design of nanoreactors for pulsed catalysis, which calls for predictive modeling of the ultrafast HC-hot adsorbate energy transfer.

Unveiling Spatiotemporal Diffusion of Hot Carriers Influenced by Spatial Nonuniform Hot Phonon Bottleneck Effect in Monolayer MoS2

The exceptional semiconducting properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) have made them highly promising for the development of future electronic and optoelectronic devices. Extensive studies of TMDs are partly associated with their ability to generate 2D-confined hot carriers above the conduction band edges, enabling potential applications that rely on such transient excited states. In this work, room-temperature spatiotemporal hot carrier dynamics in monolayer MoS2 is studied by transient absorption microscopy (TAM), featuring an initial ultrafast expansion followed by a rapid negative diffusion, and ultimately a slow long-term expansion of the band edge C-excitons. We provide direct experimental evidence to identify the abnormal negative diffusion process as a spatial contraction of the hot carriers resulting from spatial variation in the hot phonon bottleneck effect due to the Gaussian intensity distribution of the pump laser beam.

Localized surface plasmon energy dissipation in bimetallic core-shell nanostructures

Exploring the plasmon energy dissipation mechanism of bimetallic nanostructures after photoexcitation is of great significance for controlling energy transfer in plasmonic applications. The absorption, scattering, and extinction spectra of Ag@Cu, Ag@Pt, and Ag@Co core-shell nanostructures are calculated by finite element method, and the energy dissipation process is visualized by using particle trajectory and the absorbed power density distribution. The absorption/scattering ratio of the core-shell nanostructures, the shell absorptivity, the time-domain electric field as well as the extra-core electron arrangements of Ag, Cu, Pt, and Co atoms are analyzed for figuring out the energy dissipation mechanism. The results show that when a non-plasmonic metal is coated on the surface of a plasmonic metal, the plasmon energy dissipates preferentially in the shell, and the degree of dissipation depends on the imaginary part of the dielectric constant of the shell and the core. A larger dielectric constant of the shell can cause more energy to be transferred from the plasmonic metal to the shell region. This study provides the fundamental physical framework and design principles for plasmonic nanostructures.

Magnesium Nanoparticles for Surface-Enhanced Raman Scattering and Plasmon-Driven Catalysis

Nanostructures of some metals can sustain localized surface plasmon resonances, collective oscillations of free electrons excited by incident light. This effect results in wavelength-dependent absorption and scattering, enhancement of the incident electric field at the metal surface, and generation of hot carriers as a decay product. The enhanced electric field can be utilized to amplify the spectroscopic signal in surface-enhanced Raman scattering (SERS), while hot carriers can be exploited for catalytic applications. In recent years, cheaper and more earth abundant alternatives to traditional plasmonic Au and Ag have gained growing attention. Here, we demonstrate the ability of plasmonic Mg nanoparticles to enhance Raman scattering and drive chemical transformations upon laser irradiation. The plasmonic properties of Mg nanoparticles are characterized at the bulk and single particle level by optical spectroscopy and scanning transmission electron microscopy coupled with electron energy-loss spectroscopy and supported by numerical simulations. SERS enhancement factors of ∼102 at 532 and 633 nm are obtained using 4-mercaptobenzoic acid and 4-nitrobenzenethiol. Furthermore, the reductive coupling of 4-nitrobenzenethiol to 4,4'-dimercaptoazobenzene is observed on the surface of Mg nanoparticles under 532 nm excitation in the absence of reducing agents, indicating a plasmon-driven catalytic process. Once decorated with Pd, Mg nanostructures display an enhancement factor of 103 along with an increase in the rate of catalytic coupling. The results of this study demonstrate the successful application of plasmonic Mg nanoparticles in sensing and plasmon-enhanced catalysis.

Ultralow Catalytic Loading for Optimised Electrocatalytic Performance of AuPt Nanoparticles to Produce Hydrogen and Ammonia

The hydrogen evolution and nitrite reduction reactions are key to producing green hydrogen and ammonia. Antenna-reactor nanoparticles hold promise to improve the performances of these transformations under visible-light excitation, by combining plasmonic and catalytic materials. However, current materials involve compromising either on the catalytic activity or the plasmonic enhancement and also lack control of reaction selectivity. Here, we demonstrate that ultralow loadings and non-uniform surface segregation of the catalytic component optimize catalytic activity and selectivity under visible-light irradiation. Taking Pt-Au as an example we find that fine-tuning the Pt content produces a 6-fold increase in the hydrogen evolution compared to commercial Pt/C as well as a 6.5-fold increase in the nitrite reduction and a 2.5-fold increase in the selectivity for producing ammonia under visible light excitation relative to dark conditions. Density functional theory suggests that the catalytic reactions are accelerated by the intimate contact between nanoscale Pt-rich and Au-rich regions at the surface, which facilitates the formation of electron-rich hot-carrier puddles associated with the Pt-based active sites. The results provide exciting opportunities to design new materials with improved photocatalytic performance for sustainable energy applications.

The role of the plasmon in interfacial charge transfer

The lack of a detailed mechanistic understanding for plasmon-mediated charge transfer at metal-semiconductor interfaces severely limits the design of efficient photovoltaic and photocatalytic devices. A major remaining question is the relative contribution from indirect transfer of hot electrons generated by plasmon decay in the metal to the semiconductor compared to direct metal-to-semiconductor interfacial charge transfer. Here, we demonstrate an overall electron transfer efficiency of 44 ± 3% from gold nanorods to titanium oxide shells when excited on resonance. We prove that half of it originates from direct interfacial charge transfer mediated specifically by exciting the plasmon. We are able to distinguish between direct and indirect pathways through multimodal frequency-resolved approach measuring the homogeneous plasmon linewidth by single-particle scattering spectroscopy and time-resolved transient absorption spectroscopy with variable pump wavelengths. Our results signify that the direct plasmon-induced charge transfer pathway is a promising way to improve hot carrier extraction efficiency by circumventing metal intrinsic decay that results mainly in nonspecific heating.

Ultrafast Coherent Exciton Couplings and Many-Body Interactions in Monolayer WS2

Transition metal dichalcogenides (TMDs) are quantum confined systems with interesting optoelectronic properties, governed by Coulomb interactions in the monolayer (1L) limit, where strongly bound excitons provide a sensitive probe for many-body interactions. Here, we use two-dimensional electronic spectroscopy (2DES) to investigate many-body interactions and their dynamics in 1L-WS2 at room temperature and with sub-10 fs time resolution. Our data reveal coherent interactions between the strongly detuned A and B exciton states in 1L-WS2. Pronounced ultrafast oscillations of the transient optical response of the B exciton are the signature of a coherent 50 meV coupling and coherent population oscillations between the two exciton states. Supported by microscopic semiconductor Bloch equation simulations, these coherent dynamics are rationalized in terms of Dexter-like interactions. Our work sheds light on the role of coherent exciton couplings and many-body interactions in the ultrafast temporal evolution of spin and valley states in TMDs.

Hot Carrier Nanowire Transistors at the Ballistic Limit

We demonstrate experimentally nonequilibrium transport in unipolar quasi-1D hot electron devices reaching the ballistic limit at room temperature. The devices are realized with heterostructure engineering in nanowires to obtain dopant- and dislocation-free 1D-epitaxy and flexible bandgap engineering. We show experimentally the control of hot electron injection with a graded conduction band profile and the subsequent filtering of hot and relaxed electrons with rectangular energy barriers. The number of electrons passing the barrier depends exponentially on the transport length with a mean-free path of 200-260 nm, and the electrons reach the ballistic transport regime for the shortest devices with 70% of the electrons flying freely through the base electrode and the barrier reflections limiting the transport to the collector.

Evolution of Excited-State Behaviors of Gold Complexes, Nanoclusters and Nanoparticles

Metal nanomaterials have been extensively investigated owing to their unique properties in contrast to bulk counterparts. Gold nanoparticles (e. g., 3-100 nm) show quasi-continuous energy bands, while gold nanoclusters (<3 nm) and complexes exhibit discrete energy levels and display entirely different photophysical properties than regular nanoparticles. This review summarizes the electronic dynamics of these three types of gold materials studied by ultrafast spectroscopy. Briefly, for gold nanoparticles, their electronic relaxation is dominated by heat dissipation between the electrons and the lattice. In contrast, gold nanoclusters exhibit single-electron transitions and relatively long excited-state lifetimes being analogous to molecules. In gold complexes, the excited-state dynamics is dominated by intersystem crossing and phosphorescence. A detailed understanding of the photophysical properties of gold nanocluster materials is still missing and thus calls for future efforts. The fundamental insights into the discrete electronic structure and the size-induced evolution in quantum-sized nanoclusters will promote the exploration of their applications in various fields.

H-Glass Supported Hybrid Gold Nano-Islands for Visible-Light-Driven Hydrogen Evolution

Flat panel reactors, coated with photocatalytic materials, offer a sustainable approach for the commercial production of hydrogen (H2) with zero carbon footprint. Despite this, achieving high solar-to-hydrogen (STH) conversion efficiency with these reactors is still a significant challenge due to the low utilization efficiency of solar light and rapid charge recombination. Herein, hybrid gold nano-islands (HGNIs) are developed on transparent glass support to improve the STH efficiency. Plasmonic HGNIs are grown on an in-house developed active glass sheet composed of sodium aluminum phosphosilicate oxide glass (H-glass) using the thermal dewetting method at 550 °C under an ambient atmosphere. HGNIs with various oxidation states (Au0, Au+, and Au-) and multiple interfaces are obtained due to the diffusion of the elements from the glass structure, which also facilitates the lifetime of the hot electron to be ≈2.94 ps. H-glass-supported HGNIs demonstrate significant STH conversion efficiency of 0.6%, without any sacrificial agents, via water dissociation. This study unveils the specific role of H-glass-supported HGNIs in facilitating light-driven chemical conversions, offering new avenues for the development of high-performance photocatalysts in various chemical conversion reactions for large-scale commercial applications.

Metal-semiconductor heterojunction accelerates the plasmonically powered photoregeneration of biological cofactors

Photocatalysis with plasmonic nanoparticles (NPs) is emerging as an attractive strategy to make and break chemical bonds. However, the fast relaxation dynamics of the photoexcited charge carriers in plasmonic NPs often result in poor yields. The separation and extraction of photoexcited hot-charge carriers should be faster than the thermalization process to overcome the limitation of poor yield. This demands the integration of rationally chosen materials to construct hybrid plasmonic photocatalysts. In this work, the enhanced photocatalytic activity of gold nanoparticle-titanium dioxide metal-semiconductor heterostructure (Au-TiO2) is used for the efficient regeneration of nicotinamide (NADH) cofactors. The modification of plasmonic AuNPs with n-type TiO2 semiconductor enhanced the charge separation process, because of the Schottky barrier formed at the Au-TiO2 heterojunction. This led to a 12-fold increment in the photocatalytic activity of plasmonic AuNP in regenerating NADH cofactor. Detailed mechanistic studies revealed that Au-TiO2 hybrid photocatalyst followed a less-explored light-independent pathway, in comparison to the conventional light-dependent path followed by sole AuNP photocatalyst. NADH regeneration yield reached ~70% in the light-independent pathway, under optimized conditions. Thus, our study emphasizes the rational choice of components in hybrid nanostructures in dictating the photocatalytic activity and the underlying reaction mechanism in plasmon-powered chemical transformations.

How the secrets behind photocurrents are revealed in Ag-TiO2 heterostructures-based plasmonic photoelectrochemical systems: A collaborative approach of EC-SERS and photoelectrochemical methods

Plasmon-mediated chemical reactions (PMCR) have garnered growing interest as a promising concept for photocatalysis. However, in electrochemical systems at solid-liquid interfaces, the photo-induced charge transfer on the surface of metal-semiconductor heterostructures involves complex processes and mechanisms, which are still poorly understood. We explore the plasmon-mediated carrier transfer mechanism and the synergistic effect of light and electric fields on Ag-TiO2 heterostructures, through a combination of electrochemical surface-enhanced Raman spectroscopy and photoelectrochemical methods, with para-aminothiophenol (PATP) serving as a probe molecule. The results show that photocurrent responses are dependent on not only excitation wavelengths and applied potentials, but also the irreversibility of redox. The relationship between photocurrent responses and the chemical transformation between PATP and 4,4'-dimercaptoazobenzene is established, reflecting the photo-induced charge transfer of the heterostructures. The collaboration of spectroscopic and photoelectrochemical methods provide valuable insights into the chemical transformation and kinetic information of adsorbed molecules on the heterostructure during PMCR, offering opportunities for modulating of photocatalytic activities of hot carriers.

Application of photothermal effects of nanomaterials in food safety detection

Numerous nanomaterials endowed with outstanding light harvesting and photothermal conversion abilities have been extensively applied in various fields, such as photothermal diagnosis and therapy, trace substance detection, and optical imaging. Although photothermal detection methods have been established utilizing the photothermal effect of nanomaterials in recent years, there is a scarcity of reviews regarding their application in food safety detection. Herein, the recent advancements in the photothermal conversion mechanism, photothermal conversion efficiency calculation, and preparation method of photothermal nanomaterials were reviewed. In particular, the application of photothermal nanomaterials in various food hazard analyses and the newly established photothermal detection methods were comprehensively discussed. Moreover, the development and promising future trends of photothermal nanomaterial-based detection methods were discussed, which provide a reference for researchers to propose more effective, sensitive, and accurate detection methods.

Plasmon-Switched Kinetics for Formic Acid Dehydrogenation: Selective Adsorption Driven by Local Field and Hot Carriers

Understanding illumination-mediated kinetics is essential for catalyst design in plasmon catalysis. Here we prepare Pd-based plasmonic catalysts with tunable electronic structures to reveal the underlying illumination-enhanced kinetic mechanisms for formic acid (HCOOH) dehydrogenation. We demonstrate a kinetic switch from a competitive Langmuir-Hinshelwood adsorption mode in dark to a non-competitive type under irradiation triggered by local field and hot carriers. Specifically, the electromagnetic field induces a spatial-temporal separation of dehydrogenation-favorable configurations of reactant molecule HCOOH and HCOO- due to their natural different polarities. Meanwhile, the generated energetic carriers can serve as active sites for selective molecular adsorption. The hot electrons act as adsorption sites for HCOOH, while holes prefer to adsorb HCOO-. Such unique non-competitive adsorption kinetics induced by plasmon effects serves as another typical characteristic of plasmonic catalysis that remarkably differs from thermocatalysis. This work unravels unique adsorption transformations and a kinetic switching driven by plasmon nonthermal effects.

Strain-Dependent Effects on Confinement of Folded Acoustic and Optical Phonons in Short-Period (XC)m/(YC)n with X,Y (≡Si, Ge, Sn) Superlattices

Carbon-based novel low-dimensional XC/YC (with X, Y ≡ Si, Ge, and Sn) heterostructures have recently gained considerable scientific and technological interest in the design of electronic devices for energy transport use in extreme environments. Despite many efforts made to understand the structural, electronic, and vibrational properties of XC and XxY1-xC alloys, no measurements exist for identifying the phonon characteristics of superlattices (SLs) by employing either an infrared and/or Raman scattering spectroscopy. In this work, we report the results of a systematic study to investigate the lattice dynamics of the ideal (XC)m/(YC)n as well as graded (XC)10-∆/(X0.5Y0.5C)∆/(YC)10-∆/(X0.5Y0.5C)∆ SLs by meticulously including the interfacial layer thickness ∆ (≡1-3 monolayers). While the folded acoustic phonons (FAPs) are calculated using a Rytov model, the confined optical modes (COMs) and FAPs are described by adopting a modified linear-chain model. Although the simulations of low-energy dispersions for the FAPs indicated no significant changes by increasing ∆, the results revealed, however, considerable "downward" shifts of high frequency COMs and "upward" shifts for the low energy optical modes. In the framework of a bond polarizability model, the calculated results of Raman scattering spectra for graded SLs are presented as a function of ∆. Special attention is paid to those modes in the middle of the frequency region, which offer strong contributions for enhancing the Raman intensity profiles. These simulated changes are linked to the localization of atomic displacements constrained either by the XC/YC or YC/XC unabrupt interfaces. We strongly feel that this study will encourage spectroscopists to perform Raman scattering measurements to check our theoretical conjectures.

Recent Advances in Electrochemiluminescence Visual Biosensing and Bioimaging

Electrochemiluminescence (ECL) is one of the most powerful techniques that meet the needs of analysis and detection in a variety of scenarios, because of its highly analytical sensitivity and excellent spatiotemporal controllability. ECL combined with microscopy (ECLM) offers a promising approach for quantifying and mapping a wide range of analytes. To date, ECLM has been widely used to image biological entities and processes, such as cells, subcellular structures, proteins and membrane transport properties. In this review, we first introduced the mechanisms of several classic ECL systems, then highlighted the progress of visual biosensing and bioimaging by ECLM in the last decade. Finally, the characteristics of ECLM were summarized, as well as some of the current challenges. The future research interests and potential directions for the application of ECLM were also outlooked.

Localized surface plasmon resonances of size-selected large silver nanoclusters (n = 70-100) soft-landed on a C60 organic substrate

Silver nanoclusters (Agn NCs) exhibit a remarkable optical property known as localized surface plasmon resonance (LSPR) in the visible to ultraviolet wavelengths. In this study, we address the size gap in LSPR responses between small NCs and nano-islands by synthesizing large Agn NCs with a countable number of atoms (n = 70-100) using a magnetron sputtering method, which were precisely size-selected and soft-landed onto substrates. The monodispersed Agn NCs were immobilized on a pre-decorated substrate with fullerene (C60) molecules, and their LSPR behaviors were characterized using two-photon photoemission (2PPE) spectroscopy. Due to the distinct polarization selectivity of incident light associated with LSPR, the intensity ratio between p- and s-polarized lights (Ip/Is) in 2PPE spectroscopy serves as a reliable indicator of LSPR and its structural correlations. From n = 70 to 100, the Ip/Is value gradually decreases as the cluster size increases. This decrease is attributed to the enhancement of s-polarized light (Is), indicating that large Agn NCs on a C60 substrate undergo a deformation from spherical to flattened geometries, particularly above approximately n = 55.

Ultrafast light-activated polymeric nanomotors

Synthetic micro/nanomotors have been extensively exploited over the past decade to achieve active transportation. This interest is a result of their broad range of potential applications, from environmental remediation to nanomedicine. Nevertheless, it still remains a challenge to build a fast-moving biodegradable polymeric nanomotor. Here we present a light-propelled nanomotor by introducing gold nanoparticles (Au NP) onto biodegradable bowl-shaped polymersomes (stomatocytes) via electrostatic and hydrogen bond interactions. These biodegradable nanomotors show controllable motion and remarkable velocities of up to 125 μm s-1. This unique behavior is explained via a thorough three-dimensional characterization of the nanomotor, particularly the size and the spatial distribution of Au NP, with cryogenic transmission electron microscopy (cryo-TEM) and cryo-electron tomography (cryo-ET). Our in-depth quantitative 3D analysis reveals that the motile features of these nanomotors are caused by the nonuniform distribution of Au NPs on the outer surface of the stomatocyte along the z-axial direction. Their excellent motile features are exploited for active cargo delivery into living cells. This study provides a new approach to develop robust, biodegradable soft nanomotors with application potential in biomedicine.

Thermal-effect dominated plasmonic catalysis on silver nanoislands

Plasmonic metal nanostructures with the intrinsic property of localized surface plasmon resonance can effectively promote energy conversion in many applications such as photocatalysis, photothermal therapy, seawater desalinization, etc. It is known that not only are plasmonically excited hot electrons generated from metal nanostructures under light irradiation, which can effectively trigger chemical reactions, but also plasmonically induced heating simultaneously occurs. Although plasmonic catalysis has been widely explored in recent years, the underlying mechanisms for distinguishing the contribution of hot electrons from thermal effects are not fully understood. Here, a simple and efficient self-assembly system using silver nanoislands as plasmonic substrates is designed to investigate the photo-induced azo coupling reaction of nitro- and amino-groups at various temperatures. In the experiments, surface-enhanced Raman spectroscopy is employed to monitor the time and temperature dependence of plasmon-induced catalytic reactions. It was found that a combination of hot electrons and thermal effects contribute to the reactivity. The thermal effects play the dominant role in the plasmon-induced azo coupling reaction of nitro-groups, which suggests that the localized temperature must be considered in the development of photonic applications based on plasmonic nanomaterials.

Chiral Au-Pd Alloy Nanorods with Tunable Optical Chirality and Catalytically Active Surfaces

Integrating the plasmonic chirality with excellent catalytic activities in plasmonic hybrid nanostructures provides a promising strategy to realize the chiral nanocatalysis toward many chemical reactions. However, the controllable synthesis of catalytically active chiral plasmonic nanoparticles with tailored geometries and compositions remains a significant challenge. Here it is demonstrated that chiral Au-Pd alloy nanorods with tunable optical chirality and catalytically active surfaces can be achieved by a seed-mediated coreduction growth method. Through manipulating the chiral inducers, Au nanorods selectively transform into two different intrinsically chiral Au-Pd alloy nanorods with distinct geometric chirality and tunable optical chirality. By further adjusting several key synthetic parameters, the optical chirality, composition, and geometry of the chiral Au-Pd nanorods are fine-tailored. More importantly, the chiral Au-Pd alloy nanorods exhibit appealing chiral catalytic activities as well as polarization-dependent plasmon-enhanced nanozyme catalytic activity, which has great potential for chiral nanocatalysis and plasmon-induced chiral photochemistry.

Gold core@CeO2 halfshell Janus nanocomposites catalyze targeted sulfate radical for periodontitis therapy

The sulfate radical (SO4•-), known for its high reactivity and long lifespan, has emerged as a potent antimicrobial agent. Its exceptional energy allows for the disruption of vital structures and metabolic pathways in bacteria that are usually inaccessible to common radicals. Despite its promising potential, the efficient generation of this radical, particularly through methods involving enzymes and photocatalysis, remains a substantial challenge. Here, we capitalized on the peroxidase (POD)-mimicking activity and photocatalytic properties of cerium oxide (CeO2) nanozymes, integrating these properties with the enhanced concept of plasma gold nanorod (GNR) to develop a half-encapsulated core@shell GNRs@CeO2 Janus heterostructure impregnated with persulfate. Under near-infrared irradiation, the GNRs generate hot electrons, thereby boosting the CeO2's enzyme-like activity and initiating a potent reactive oxygen species (ROS) storm. This distinct nanoarchitecture facilitates functional specialization, wherein the heterostructure and efficient light absorption ensured continuous hot electron flow, not only enhancing the POD-like activity of CeO2 for the production of SO4•- effectively, but also contributing a significant photothermal effect, disrupting periodontal plaque biofilm and effectively eradicating pathogens. Furthermore, the local temperature elevation synergistically enhances the POD-like activity of CeO2. Transcriptomics analysis, as well as animal experiments of the periodontitis model, have revealed that pathogens undergo genetic information destruction, metabolic disorders, and pathogenicity changes in the powerful ROS system, and profound therapeutic outcomes in vivo, including anti-inflammation and bone preservation. This study demonstrated that energy transfer to augment nanozyme activity, specifically targeting ROS generation, constitutes a significant advancement in antibacterial treatment.

Focusing Surface Acoustic Waves with a Plasmonic Hypersonic Lens

Plasmonic nanoantennas have proven to be efficient transducers of electromagnetic to mechanical energy and vice versa. The sudden thermal expansion of these structures after an ultrafast optical pulsed excitation leads to the emission of hypersonic acoustic waves to the supporting substrate, which can be detected by another antenna that acts as a high-sensitivity mechanical probe due to the strong modulation of its optical response. Here, we propose and experimentally demonstrate a nanoscale acoustic lens comprised of 11 gold nanodisks whose collective oscillation at gigahertz frequencies gives rise to an interference pattern that results in a diffraction-limited surface acoustic beam of about 340 nm width, with an amplitude contrast of 60%. Via spatially decoupled pump-probe experiments, we were able to map the radiated acoustic energy in the proximity of the focal area, obtaining a very good agreement with the continuum elastic theory.