Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance（LSPR） enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts.In the past decades,noble metal nanoparticles（Au and Ag） with LSPR feature have found wide applications in solar energy conversion.Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures.However,high cost and...     

Trends and challenges of refractometric nanoplasmonic biosensors: A review

Motivated by potential benefits such as sensor miniaturization, multiplexing opportunities and higher sensitivities, refractometric nanoplasmonic biosensing has profiled itself in a short time span as an interesting alternative to conventional Surface Plasmon Resonance (SPR) biosensors. This latter conventional sensing concept has been subjected during the last decades to strong commercialization, thereby strongly leaning on well-developed thin-film surface chemistry protocols. Not surprisingly, the examples found in literature based on this sensing concept are generally characterized by extensive analytical studies of relevant clinical and diagnostic problems. In contrast, the more novel Localized Surface Plasmon Resonance (LSPR) alternative finds itself in a much earlier, and especially, more fundamental stage of development. Driven by new fabrication methodologies to create nanostructured substrates, published work typically focuses on the novelty of the presented material, its optical properties and its use – generally limited to a proof-of-concept – as a label-free biosensing scheme. Given the different stages of development both SPR and LSPR sensors find themselves in, it becomes apparent that providing a comparative analysis of both concepts is not a trivial task. Nevertheless, in this review we make an effort to provide an overview that illustrates the progress booked in both fields during the last five years. First, we discuss the most relevant advances in SPR biosensing, including interesting analytical applications, together with different strategies that assure improvements in performance, throughput and/or integration. Subsequently, the remaining part of this work focuses on the use of nanoplasmonic sensors for real label-free biosensing applications. First, we discuss the motivation that serves as a driving force behind this research topic, together with a brief summary that comprises the main fabrication methodologies used in this field. Next, the sensing performance of LSPR sensors is examined by analyzing different parameters that can be invoked in order to quantitatively assess their overall sensing performance. Two aspects are highlighted that turn out to be especially important when trying to maximize their sensing performance, being (1) the targeted functionalization of the electromagnetic hotspots of the nanostructures, and (2) overcoming inherent negative influence that stem from the presence of a high refractive index substrate that supports the nanostructures. Next, although few in numbers, an overview is given of the most exhaustive and diagnostically relevant LSPR sensing assays that have been recently reported in literature, followed by examples that exploit inherent LSPR characteristics in order to create highly integrated and high-throughput optical biosensors. Finally, we discuss a series of considerations that, in our opinion, should be addressed in order to bring the realization of a stand-alone LSPR biosensor with competitive levels of sensitivity, robustness and integration (when compared to a conventional SPR sensor) much closer to reality.     

Surface-enhanced Raman spectroscopy toward application in plasmonic photocatalysis on metal nanostructures

Among photothermal, photovoltaic and photochemical techniques, photochemistry is superior in energy storage and transportation by converting photons into chemical fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochemical reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resolution. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity analysis, latest studies of SERS applied for the plasmon mediated photochemical reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.     

Plasmonic properties of silver nanostructures coated with an amorphous silicon-carbon alloy and their applications for sensitive sensing of DNA hybridization

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.     

Wide-field single metal nanoparticle spectroscopy for high throughput localized surface plasmon resonance sensing

Noble metal nanoparticles (mNPs) have a distinct extinction spectrum arising from their ability to support Localized Surface Plasmon Resonance (LSPR). Single-particle biosensing with LSPR is label free and offers a number of advantages, including single molecular sensitivity, multiplex detection, and in vivo quantification of chemical species etc. In this article, we introduce Single-particle LSPR Imaging (SLI), a wide-field spectral imaging method for high throughput LSPR biosensing. The SLI utilizes a transmission grating to generate the diffraction spectra from multiple mNPs, which are captured using a Charge Coupled Device (CCD). With the SLI, we are able to simultaneously image and track the spectral changes of up to 50 mNPs in a single (～1 s) exposure and yet still retain a reasonable spectral resolution for biosensing. Using the SLI, we could observe spectral shift under different local refractive index environments and demonstrate biosensing using biotin-streptavidin as a model system. To the best of our knowledge, this is the first time a transmission grating based spectral imaging approach has been used for mNPs LSPR sensing. The higher throughput LSPR sensing, offered by SLI, opens up a new possibility of performing label-free, single-molecule experiments in a high-throughput manner.     

Understanding plasmonic catalysis with controlled nanomaterials based on catalytic and plasmonic metals

Recently, it has been established that the localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can be put toward the acceleration and control of molecular transformations. This field, named plasmonic catalysis, has emerged as a new frontier in nanocatalysis. For metals such as silver (Ag), gold (Au), and copper (Cu), the LSPR excitation can take place in the visible and near-infrared ranges, opening possibilities for the conversion of solar to chemical energy and new/alternative reaction pathways not accessible via conventional, thermally activated catalytic processes. As both catalytic and optical properties can be tuned by controlling several physical and chemical parameters at the nanoscale, design-controlled nanomaterials open the door to unlock the potential of plasmonic catalysis both in terms of fundamental understanding and optimization of performances. In this context, after introducing the fundamentals of plasmonic catalysis, we provide an overview on the current understanding of this field enabled by the utilization of designed-controlled nanostructures based on plasmonic and catalytic metals as model systems. We start by discussing trends in plasmonic catalytic performances and their correlation with nanoparticle size, shape, composition, and structure. Then, we highlight how multimetallic compositions and morphologies containing both catalytic and plasmonic components enables one to extend the use of plasmonic catalysis to metals that are important in catalysis but do not support LSPR excitation in the visible range. Finally, we focus on key challenges and perspectives that are critically important to assist us in designing future energy-efficient plasmonic-catalytic materials.     

Sensing using localised surface plasmon resonance sensors

The bright colours of noble metal particles have attracted considerable interest since historical times, where they were used as decorative pigments in stained glass windows. More recently, the tuneable optical properties of metal nanoparticles and their addressability via spectroscopic techniques have brought them back into the forefront of fundamental and applied research fields. Much of the recent attention concerning metal nanoparticles such as gold and silver has been their use as small-volume, ultra-sensitive label-free optical sensors. Plasmonic nanoparticles act in this case as transducers that convert changes in the local refractive index into spectral shifts of the localized surface plasmon resonance (LSPR) band. This LSPR-shift assay is a general technique for measuring binding affinities and rates from any molecule that induces a change in the local refractive index around the metallic nanostructures. By attaching molecular recognition elements (chemical or biological ligands) on the nanostructures, specificity and selectivity to the analyte of interest are introduced into the nanosensor. In this review, we will discuss the different methods used to fabricate plasmonic nanosensors. A special emphasis will be given to techniques used to link plasmonic nanostructures to surfaces. While the difference between colorimetric and refractive index sensing approaches will be briefly described, the importance to distinguish between bulk refractive index (RI) sensing and molecular near-field refractive index sensing will be discussed. The recent progress made in the development of novel surface functionalization strategies together with the formation of optically and mechanically stable LSPR sensors will be highlighted.     

Sensitive biosensing strategy based on functional nanomaterials

The first decade of the 21st century has been labeled as the sensing decade. The functional nanomaterials offer excellent platforms for fabrication of sensitive biosensing devices, including optical and electronic biosensors. A lot of works have fo- cused on the biofunctionalization of different nanomaterials, such as metal nanoparticles, semiconductor nanoparticles and carbon nanostructures, by physical adsorption, electrostatic binding, specific recognition or covalent coupling. These biofunc- tionalized ...     

Full Solution‐Processed Synthesis and Mechanisms of a Recyclable and Bifunctional Au/ZnO Plasmonic Platform for Enhanced UV/Vis Photocatalysis and Optical Properties

The synthesis of noble metal/semiconductor hybrid nanostructures for enhanced catalytic or superior optical properties has attracted a lot of attention in recent years. In this study, a facile and all‐solution‐processed synthetic route was employed to demonstrate an Au/ZnO platform with plasmonic‐enhanced UV/Vis catalytic properties while retaining strengthened luminescent properties. The visible‐light response of photocatalysis is supported by localized surface plasmon resonance (LSPR) excitations while the enhanced performance under UV is aided by charge separation and strong absorption. The enhancement in optical properties is mainly due to local field enhancement effect and coupling between exciton and LSPR. Luminescent characteristics are investigated and discussed in detail. Recyclability tests showed that the Au/ZnO substrate is reusable by cleaning and has a long shelf life. Our result suggests that plasmonic enhancement of photocatalytic performance is not necessarily a trade‐off for enhanced near‐band‐edge emission in Au/ZnO. This approach may give rise to a new class of versatile platforms for use in novel multifunctional and integrated devices.     

Localized surface plasmon resonance: nanostructures, bioassays and biosensing--a review

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles (NPs) that are smaller than the incident wavelength. As in surface plasmon resonance, the electric field of incident light can be deposited to collectively excite electrons of a conduction band, with the result being coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of NPs. This review serves to describe the physical theory of LSPR formation at the surface of nanostructures, and the potential for this optical technology to serve as a basis for the development bioassays and biosensing of high sensitivity. The benefits and challenges associated with various experimental designs of nanoparticles and detection systems, as well as creative approaches that have been developed to improve sensitivity and limits of detection are highlighted using examples from the literature.     

Amorphous Materials for Enhanced Localized Surface Plasmon Resonances

The discovery of localized surface plasmon resonance (LSPR) in semiconductor nanocrystals has initiated a new field in plasmonics. Plasmonic nanocrystals in particular have seen rapid development in recent years because they are a class of materials with unique photoelectronic properties. At present, a growing number of amorphous plasmonic materials has been steadily capturing scientific interest, though only a few of these are well characterized. Here we focus on recent developments in state‐of‐the art experiments and explore the vast library of plasmonic properties in amorphous materials, including their application fields and optical spectral range. Taken together, the growing regime of amorphous material plasmonics offers enticing avenues for harnessing light–matter interactions from the visible to the terahertz region, with new potential for optical manipulation beyond what can be accomplished using traditional crystal materials.     

Plasmonic Titanium Nitride Tubes Decorated with Ru Nanoparticles as Photo-Thermal Catalyst for CO2 Methanation

Photo-thermal catalysis has recently emerged as a viable strategy to produce solar fuels or chemicals using sunlight. In particular, nanostructures featuring localized surface plasmon resonance (LSPR) hold great promise as photo-thermal catalysts given their ability to convert light into heat. In this regard, traditional plasmonic materials include gold (Au) or silver (Ag), but in the last years, transition metal nitrides have been proposed as a cost-efficient alternative. Herein, we demonstrate that titanium nitride (TiN) tubes derived from the nitridation of TiO₂ precursor display excellent light absorption properties thanks to their intense LSPR band in the visible–IR regions. Upon deposition of Ru nanoparticles (NPs), Ru-TiN tubes exhibit high activity towards the photo-thermal CO₂ reduction reaction, achieving remarkable methane (CH₄) production rates up to 1200 mmol g⁻¹ h⁻¹. Mechanistic studies suggest that the reaction pathway is dominated by thermal effects thanks to the effective light-to-heat conversion of Ru-TiN tubes. This work will serve as a basis for future research on new plasmonic structures for photo-thermal applications in catalysis.     

Enhancement of Nonlinear Optical Scattering by Gold Nanoparticles through Aggregation-Induced Plasmon Coupling in the Near-Infrared

Gold nanoparticles (AuNPs) are regarded as promising building blocks in functional nanomaterials for sensing, drug delivery and catalysis. One remarkable property of these particles is the localized surface plasmon resonance (LSPR), which gives rise to augmented optical properties through local field enhancement. LSPR also influences the nonlinear optical properties of metal NPs (MNPs) making them potentially interesting candidates for fast, high resolution nonlinear optical imaging. In this work we characterize and discuss the wavelength dependence of the hyper-Rayleigh scattering (HRS) behavior of spherical gold nanoparticles (GNP) and gold nanorods (GNR) in solution, from 850 nm up to 1300 nm, covering the near-infrared (NIR) window relevant for deep tissue imaging. The high-resolution spectral data allows discriminating between HRS and two photon photoluminescence contributions. Upon particle aggregation, we measured very large enhancements (ca. 10⁴) of the HRS intensity in the NIR, which is explained by considering aggregation-induced plasmon coupling effects and local field enhancement. These results indicate that purposely designed coupled nanostructures could prove advantageous for nonlinear optical imaging and biosensing applications.     

Inside Back Cover: Surfactant Directed Synthesis of Intrinsically Chiral Plasmonic Nanostructures and Precise Tuning of their Optical Activity through Controlled Self-Assembly (Angew. Chem. Int. Ed. 21/2023)

Fabrication and transmission of plasmonic chirality is a rapidly developing area of research. While nanoscale chirality is reasonably well explored, research on intrinsically chiral nanostructures, that has ramifications to origin of homochirality, is still in its infancy. Herein, we report the synthesis of dog-bone shaped chiral gold nanostructures using a chiral cationic surfactant with excess ascorbic acid. Chiral growth is attributed to the specific binding and structure breaking ability of chiral surfactant and ascorbic acid. The controlled assembly of particles facilitated tuning and enhancement of chiral signals. Experimental observations were validated with theoretical simulations modelled in frequency domain with a surface integral-equation parameterization. Work highlighting the generation and tuning of plasmonic chirality provides new insights into the understanding of intrinsic chirality and paves way for their application in enantioselective catalysis and biosensing.     

等离子体金属纳米结构在SERS传感及可穿戴应力传感中的应用

等离子体金属(金、银)纳米结构因其特有的理化性能,被广泛应用于表面增强拉曼散射(Surface-enhanced Raman scattering,SERS)传感及可穿戴应力传感领域.其中,SERS是一种应用贵金属纳米材料增强拉曼散射信号的检测技术,该技术灵敏度高、特异性强,已被广泛用于生物医学、环境监测、食品药品检测...     

Recent Advances in Plasmonic Nanostructures Applied for Label-free Single-cell Analysis

Cellular heterogeneity presents a major challenge in understanding the relationship between cells of particular genotype and response in disease. In order to characterize the cell-to-cell differences during the biochemical processes, single-cell analysis is necessary. Profiting from the unique localized surface plasmon resonance (LSPR) and Mie scattering, plasmonic nanostructures have revealed stable and adjustable scattering signals, avoiding photobleaching, blinking and autofluorescence phenomenon. These characterizations are propitious to the dynamic trace and biological image of single living cells. In this review, we discuss the recent advances in plasmonic nanostructures applied for label-free detection and monitoring of target cells at single-cell level by using three different techniques, surface-enhanced Raman scattering (SERS), surface-enhanced Infrared absorption spectroscopy (SEIRAS), and dark-field microscopy. Various avenues to design plasmonic probes combining spectra and imaging for single-cell analysis are demonstrated as well. We hope this review can highlight the superiority of plasmonic nanostructures in single cellular analysis, and further motivate the development of label-free cell analysis technique to elucidate cellular diversity and heterogeneity.     

Surfactant‐Free Nonaqueous Synthesis of Plasmonic Molybdenum Oxide Nanosheets with Enhanced Catalytic Activity for Hydrogen Generation from Ammonia Borane under Visible Light

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth‐abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface‐capping agents in their synthetic procedures. To fulfill this, a facile non‐aqueous procedure was employed to prepare well‐defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO_3‐x nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near‐infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen‐generation activity of ammonia borane under visible light irradiation.     

Ag纳米粒子修饰光纤探针在等离激元催化反应中的应用

本文发展了一种基于Ag纳米粒子(AgNPs)修饰的局域表面等离激元共振(LSPR)光纤探针,作为等离激元催化反应基底同时原位检测表面增强拉曼光谱(SERS)信号,实现反应与检测一体化。本文使用(3-氨基丙基)三甲氧基硅烷(APTMS)分子将AgNPs组装到光纤探针表面。通过调控自组装时间,可形成AgNPs均匀分布的探针。以对巯基苯胺(PATP)作为反应的模型分子,获得了较好的等离激元催化及信号检测效果。在相同光源条件下,从光纤内部激发收集所得产物的SERS信号强度为外部激发收集的12.8倍,表明内激发收集方式在反应及信号检测方面具有优势;在一定浓度范围(10~(-4)–10~(-8)mol·L~(-1))内可用该光纤探针对PATP溶液进行定量分析;运用该光纤探针开展了等离激元催化PATP分子偶联反应的原位动力学研究。该LSPR光纤探针具有较高灵敏度,对样品损伤小,可在多场合下实现原位检测,且制备简便、成本较低。还有望结合近场扫描光学显微技术进一步对样品表面进行微区等离激元催化反应及检测并得到反应的二维分布图。     

Synthesis of Au@Ag core-shell nanocubes containing varying shaped cores and their localized surface plasmon resonances

We have synthesized Au@Ag core-shell nanocubes containing Au cores with varying shapes and sizes through modified seed-mediated methods. Bromide ions are found to be crucial in the epitaxial growth of Ag atoms onto Au cores and in the formation of the shell's cubic shape. The Au@Ag core-shell nanocubes exhibit very abundant and distinct localized surface plasmon resonance (LSPR) properties, which are core-shape and size-dependent. With the help of theoretical calculation, the physical origin and the resonance mode profile of each LSPR peak are identified and studied. The core-shell nanocrystals with varying shaped cores offer a new rich category for LSPR control through the plasmonic coupling effect between core and shell materials.     

Template-assisted self-assembly of achiral plasmonic nanoparticles into chiral structures

The acquisition of strong chiroptical activity has revolutionized the field of plasmonics, granting access to novel light–matter interactions and revitalizing research on both the synthesis and application of nanostructures. Among the different mechanisms for the origin of chiroptical properties in colloidal plasmonic systems, the self-assembly of achiral nanoparticles into optically active materials offers a versatile route to control the structure–optical activity relationships of nanostructures, while simplifying the engineering of their chiral geometries. Such unconventional materials include helical structures with a precisely defined morphology, as well as large scale, deformable substrates that can leverage the potential of periodic patterns. Some promising templates with helical structural motifs like liquid crystal phases or confined block co-polymers still need efficient strategies to direct preferential handedness, whereas other templates such as silica nanohelices can be grown in an enantiomeric form. Both types of chiral structures are reviewed herein as platforms for chiral sensing: patterned substrates can readily incorporate analytes, while helical assemblies can form around structures of interest, like amyloid protein aggregates. Looking ahead, current knowledge and precedents point toward the incorporation of semiconductor emitters into plasmonic systems with chiral effects, which can lead to plasmonic–excitonic effects and the generation of circularly polarized photoluminescence.

Diverse templating materials and assembly strategies can be used to induce collective optical activity on achiral plasmonic building blocks. We present the advances, applications, challenges, and prospects of plasmonic–excitonic hybrids.