Plasmon-enhanced Raman Spectroscopy Research Articles

Plasmon-enhanced Raman spectroscopy to estimate near-electric-field enhancement

Plasmon-enhanced Raman spectroscopy to estimate near-electric-field enhancement

(Invited) Multiscale Interfacial Heterogeneity Explored by Advanced Spectroscopy and Imaging for Batteries Beyond Lithium-Ion

Keywords: solid-liquid interface, solid-state battery, surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), neutron tomography, sulfide solid-state electrolyte, Raman imagingThe ever-growing needs for energy storage systems require batteries with even higher power and energy density with extended life and enhanced safety beyond the current Li-ion battery technologies. Fulfilling these needs requires new battery chemistries, including high-energy-density electrode materials, solid-state electrolytes, and efficient interphases to mitigate the side reactions between the electrodes and the electrolytes.Charge transport across the electrode and electrolyte interface is believed to be one of the charge/discharge rate-limiting steps. Although the composition, morphology, and structure of solid-electrolyte interphase (SEI) have been extensively studied, probing its evolution at the nanoscale is challenging to a large extent. Plasmon-enhanced Raman spectroscopy (PERS) is promising to solve this challenge. PERS is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity molecules stimulated by incident light. It includes surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). In the first part of this talk, I will show that gap-mode SERS is ideal to probe salt solvation structure in the immediate vicinity (< 20 nm) of the electrode/electrolyte interface. SERS lacks the nanoscale resolution in the sample plane. This can be compensated by TERS. TERS analysis on cycled high-energy silicon anodes indicates that the nanometer scale SEI "islands" are unevenly distributed. Even for the same SEI "island", the composition is different from point to point with inter-point distance smaller than 10 nm.All-solid-state lithium metal batteries (SSBs) promise specific energy >500 Wh/kg. A solid-state electrolyte (SSE) plays an irreplaceable role in reaching such an energy-density goal. Sulfide-based SSEs have emerged as a prominent class of soft ionic conductors that have comparable room-temperature ionic conductivity to their liquid electrolyte counterparts. However, when paring with a high voltage cathode, such as lithium nickel manganese cobalt oxide (NMC), the (electro)chemical instability of the sulfide SSE at the electrode/SSE interfaces becomes a major challenge. The interfacial instability can result in >50% initial capacity loss in a Li/sulfide SSE/NMC battery, thereby keeping the sulfide SSEs from commercialization. In the second part of this talk, I will show how we synergistically use neutron computed tomography and in situ Raman imaging, with clustering analysis to track lithium displacement at the interface of a sulfide-based SSB. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program. This research used resources at High Flux Isotope Reactor, a DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.

A Full Quantum Mechanical Approach Assessing the Chemical and Electromagnetic Effect in TERS.

Tip-enhanced Raman spectroscopy (TERS) is a valuable method for surface analysis with nanometer to angstrom-scale resolution; however, the accurate simulation of particular TERS signals remains a computational challenge. We approach this challenge by combining the two main contributors to plasmon-enhanced Raman spectroscopy and to the high resolution in TERS, in particular, the electromagnetic and the chemical effect, into one quantum mechanical simulation. The electromagnetic effect describes the sample's interaction with the strong, highly localized, and inhomogeneous electric fields associated with the plasmonic tip and is typically the thematic focus for most mechanistic studies. On the other hand, the chemical effect covers the different responses to the extremely close-range and highly position-sensitive chemical interaction between the apex tip atom(s) and the sample, and, as we could show in previous works, plays an often underestimated role. Starting from a (time-dependent) density functional theory description of the chemical model system, comprised of a tin(II) phthalocyanine sample molecule and a single silver atom as the tip, we introduce the electromagnetic effect through a series of static point charges that recreate the electric field in the vicinity of the plasmonic Ag nanoparticle. By scanning the tip over the molecule along a 3D grid, we can investigate the system's Raman response on each position for nonresonant and resonant illumination. Simulating both effects on their own already hints at the achievable signal enhancement and resolution, but the combination of both creates even stronger evidence that TERS is capable of resolving submolecular features.

Resolving nanostructure and chemistry of solid-electrolyte interphase on lithium anodes by depth-sensitive plasmon-enhanced Raman spectroscopy

The solid-electrolyte interphase (SEI) plays crucial roles for the reversible operation of lithium metal batteries. However, fundamental understanding of the mechanisms of SEI formation and evolution is still limited. Herein, we develop a depth-sensitive plasmon-enhanced Raman spectroscopy (DS-PERS) method to enable in-situ and nondestructive characterization of the nanostructure and chemistry of SEI, based on synergistic enhancements of localized surface plasmons from nanostructured Cu, shell-isolated Au nanoparticles and Li deposits at different depths. We monitor the sequential formation of SEI in both ether-based and carbonate-based dual-salt electrolytes on a Cu current collector and then on freshly deposited Li, with dramatic chemical reconstruction. The molecular-level insights from the DS-PERS study unravel the profound influences of Li in modifying SEI formation and in turn the roles of SEI in regulating the Li-ion desolvation and the subsequent Li deposition at SEI-coupled interfaces. Last, we develop a cycling protocol that promotes a favorable direct SEI formation route, which significantly enhances the performance of anode-free Li metal batteries.

Ion-Mediated Protein Stabilization on Nanoscopic Surfaces.

The emergence of nanoparticles in biomedical applications has made their interactions with proteins inevitable. Nanoparticles conjugated with proteins and peptide-based constructs form an integral part of nanotherapeutics and have recently shown promise in treating a myriad of diseases. The proper functioning of proteins is critical to achieve their biological functions. However, interface issues result in the denaturation of proteins, and the loss of orientation and steric hindrance can adversely affect the function of the conjugate. Furthermore, surface-induced denaturation also triggers protein aggregation, resulting in amyloid-like species. Understanding the mechanistic underpinnings of protein-nanoparticle interactions and controlling their interfacial characteristics are critical and challenging due to the complex nature of the conjugates. In this milieu, we demonstrate that ionic liquids can be suitable candidates for stabilizing protein-nanoparticle interactions by virtue of their excellent protein-preserving properties. We also probe the previously unexplored mechanism of ion-mediated stabilization of the protein molecules on the nanoparticle surface. The protein-nanoparticle conjugates consist of lysozyme and choline-based ionic liquids characterized by optical and electron microscopy techniques combined with surface-sensitive plasmon-enhanced Raman spectroscopy. Furthermore, atomistic molecular dynamics simulations of the conjugates delineate interfacial interactions of the protein molecules and the modulation by the ions, particularly the conformational changes and the dynamic correlation when the protein and specific ionic liquid molecules are adsorbed on the nanoparticle surface. The combined experimental and computational studies showed the synergistic behavior of the ions of the ionic liquids, specifically the orientation and coverage of the anions aided by the cations to control the surface interactions and hence the overall protein stability. These studies pave the way for using ionic liquids, particularly their biocompatible counterparts in nanoparticle-based complexes, as stabilizing agents for biomedical applications.

Comparing Commercial Metal-Coated AFM Tips and Home-Made Bulk Gold Tips for Tip-Enhanced Raman Spectroscopy of Polymer Functionalized Multiwalled Carbon Nanotubes.

Tip-enhanced Raman spectroscopy (TERS) combines the high specificity and sensitivity of plasmon-enhanced Raman spectroscopy with the high spatial resolution of scanning probe microscopy. TERS has gained a lot of attention from many nanoscience fields, since this technique can provide chemical and structural information of surfaces and interfaces with nanometric spatial resolution. Multiwalled carbon nanotubes (MWCNTs) are very versatile nanostructures that can be dispersed in organic solvents or polymeric matrices, giving rise to new nanocomposite materials, showing improved mechanical, electrical and thermal properties. Moreover, MWCNTs can be easily functionalized with polymers in order to be employed as specific chemical sensors. In this context, TERS is strategic, since it can provide useful information on the cooperation of the two components at the nanoscale for the optimization of the macroscopic properties of the hybrid material. Nevertheless, efficient TERS characterization relies on the geometrical features and material composition of the plasmonic tip used. In this work, after comparing the TERS performance of commercial Ag coated nanotips and home-made bulk Au tips on bare MWCNTs, we show how TERS can be exploited for characterizing MWCNTs mixed with conjugated fluorene copolymers, thus contributing to the understanding of the polymer/CNT interaction process at the local scale.

Recent Developments in Plasmonic Sensors of Phenol and Its Derivatives

Many scientists are increasingly interested in on-site detection methods of phenol and its derivatives because these substances have been universally used as a significant raw material in the industrial manufacturing of various chemicals of antimicrobials, anti-inflammatory drugs, antioxidants, and so on. The contamination of phenolic compounds in the natural environment is a toxic response that induces harsh impacts on plants, animals, and human health. This mini-review updates recent developments and trends of novel plasmonic resonance nanomaterials, which are assisted by various optical sensors, including colorimetric, fluorescence, localized surface plasmon resonance (LSPR), and plasmon-enhanced Raman spectroscopy. These advanced and powerful analytical tools exhibit potential application for ultrahigh sensitivity, selectivity, and rapid detection of phenol and its derivatives. In this report, we mainly emphasize the recent progress and novel trends in the optical sensors of phenolic compounds. The applications of Raman technologies based on pure noble metals, hybrid nanomaterials, and metal–organic frameworks (MOFs) are presented, in which the remaining establishments and challenges are discussed and summarized to inspire the future improvement of scientific optical sensors into easy-to-operate effective platforms for the rapid and trace detection of phenol and its derivatives.

In-operando surface-sensitive probing of electrochemical reactions on nanoparticle electrocatalysts: Spectroscopic characterization of reaction intermediates and elementary steps of oxygen reduction reaction on Pt

In this paper we present an in-operando spectroscopic study of the reaction intermediates involved in ORR on electrified Pt nanoparticle electrocatalysts. To accomplish this, we have synthesized Ag-Pt core–shell nanoparticles, that contain a thin shell of Pt (~1 nm) uniformly deposited on a larger Ag core (~60 nm). We show that these nanostructures are ideal platforms for in-operando Plasmon Enhanced Raman Spectroscopy (PERS) of ORR on Pt. We combined these PERS studies with DFT calculations to assign the measured vibrational spectra to relevant surface intermediates as a function of electrocatalyst potential. These vibrational assignments were further verified and validated by performing PERS measurements using de-oxygenated and heavy oxygen (O2-18) saturated electrolyte. These studies allowed us to identity the presence of critical reaction intermediates (OH, O2, OOH, and H2O) as the function of operating voltage on the Pt surface and derive voltage-dependent elementary step mechanisms of the reaction.

Recent advances in plasmon-enhanced Raman spectroscopy for catalytic reactions on bifunctional metallic nanostructures.

Metallic nanostructures exhibit superior catalytic performance for diverse chemical reactions and the in-depth understanding of reaction mechanisms requires versatile characterization methods. Plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), and tip-enhanced Raman spectroscopy (TERS), appears as a powerful technique to characterize the Raman fingerprint information of surface species with high chemical sensitivity and spatial resolution. To expand the range of catalytic reactions studied by PERS, catalytically active metals are integrated with plasmonic metals to produce bifunctional metallic nanostructures. In this minireview, we discuss the recent advances in PERS techniques to probe the chemical reactions catalysed by bifunctional metallic nanostructures. First, we introduce different architectures of these dual-functionality nanostructures. We then highlight the recent works using PERS to investigate important catalytic reactions as well as the electronic and catalytic properties of these nanostructures. Finally, we provide some perspectives for future PERS studies in this field.

Plasmon-driven photocatalytic molecular transformations on metallic nanostructure surfaces: mechanistic insights gained from plasmon-enhanced Raman spectroscopy

This Review Article elaborates on the insights gained from in situ plasmon-enhanced Raman spectroscopy, which shed light on the complex mechanisms underpinning plasmon-driven photocatalytic molecular transformations on nanostructured metal surfaces.

Long-Range Surface Plasmon Enhanced Raman Spectroscopy at Catalytic Platinum Electrodes

Surface enhanced Raman scattering (SERS) is recognized as a powerful method for in-situ observation of electrode/electrolyte interfaces, due to the high chemical sensitivity and surface selectivity. However, the applicability of this technique is limited by the nature of surface plasmon resonances at the interface. Although platinum group metals (PGMs) are one of the most interesting materials for electrocatalysis, surface plasmon polaritons are largely damped at these metal surfaces by their localized d-electrons near the Fermi level. Thus, the plasmon enhanced Raman spectroscopy is normally useless for studying such catalytic surfaces. So far, the signal enhancement factors reported at PGM surfaces are in the order of 102 while those at coinage metal surfaces can reach the order of 106 to 1010. In order to gain more intensity at highly damping PGM surfaces, the intensity-borrowing method is a common method; for example, when a large number of Au nanoparticles are deposited on a PGM surface, Raman scattering signals are largely enhanced by the sphere-plane type coupled plasmon modes [1,2]. However, such a nanostructure may influence mass transport, selectivity, and reactivity of electrochemical reactions. For spectro-electrochemistry, it is necessary to reduce the plasmon damping without suffering from such a nanoscale effect. In this work, the attenuation of surface plasmons at highly damping Pt surface is reduced using a symmetric slab mode, which is a strongly coupled surface plasmons excited at both interfaces of a thin metal film [3]. The prolonged propagation of surface plasmons in this double-interface configuration leads to a substantial enhancement of local fields even at lossy Pt surface. The theoretical calculation indicates that the enhancement factor of Raman scattering intensity can reach the order of 104 at Pt/solution interfaces in this coupled plasmon mode. We experimentally demonstrate that Raman scattering signals are significantly enhanced at Pt surface under electrochemical conditions. This strategy provides us a novel surface-specific spectroscopic method for the molecular-scale investigation of electrocatalytic reactions.[1] J. Hu, N. Hoshi, K. Uosaki, K. Ikeda, Nano Lett., 15, 7982-7986 (2015).[2] J. Hu, M. Tanabe, J. Sato, K. Uosaki, K. Ikeda, J. Am. Chem. Soc.,136, 10299-10307 (2014).[3] S. Ikegaya, K. Motobayashi, K. Ikeda, J. Raman Spectrosc. DOI: 10.1002/jrs.5925 (2020)

Long‐range surface plasmon enhanced Raman spectroscopy at highly damping platinum electrodes

AbstractKnowledge of electrode/electrolyte interfacial structures is the first step toward a better understanding of electrochemical reactions. Among several surface‐specific vibrational spectroscopy, plasmonic enhancement of Raman scattering signals is recognized as a powerful method for in situ observation of electrochemical metal/dielectric interfaces. However, the applicability of this technique is governed by the resonance behavior of surface plasmons at the interface. Although platinum group metals are one of the most interesting materials for electrocatalysis, surface plasmon polaritons are largely damped at these surfaces by their localized d‐electrons. Thus, the plasmon enhanced Raman spectroscopy is normally useless for studying such catalytic surfaces. In this work, the attenuation of surface plasmons at highly damping Pt surface is reduced using a symmetric slab mode, which is a strongly coupled surface plasmons excited at both interfaces of a thin metal film. The prolonged propagation of surface plasmons in this double‐interface configuration leads to a substantial enhancement of local fields even at lossy Pt surface. The theoretical calculation indicates that the enhancement factor of Raman scattering intensity can reach the order of 104 at Pt/solution interfaces in this coupled plasmon mode. We experimentally demonstrate that Raman scattering signals are indeed significantly enhanced at Pt surface under electrochemical conditions. This strategy provides us a novel surface‐specific spectroscopic method for the molecular‐scale investigation of electrocatalytic reactions.

Fundamental understanding and applications of plasmon-enhanced Raman spectroscopy

Plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy, shell-isolated nanoparticle-enhanced Raman spectroscopy and tip-enhanced Raman spectroscopy, has witnessed substantial development over the past 20 years. These techniques can provide fingerprint information on target materials with sensitivities down to the single-molecule level and with sufficient spatial resolution to observe individual vibrational modes. PERS has thus found applications in diverse areas, ranging from bioanalysis to materials characterization. In this Technical Review, we survey the fundamental principles, advantages and limitations of using localized surface plasmon resonance to enhance the Raman signal in PERS. We discuss the issues that influence the sensitivity and interpretation of PERS results and provide an overview of state-of-the-art PERS applications in materials characterization, bioanalysis and the study of surfaces and interfaces. We also troubleshoot common experimental issues, largely based on our own experience. Finally, we conclude by examining future directions and issues to be addressed for the further development of PERS techniques. Plasmon-enhanced Raman spectroscopy (PERS) is a highly sensitive technique that can provide molecular fingerprint information. This Technical Review discusses the fundamental principles, advantages and limitations of PERS, key issues in using PERS and interpreting results, and state-of-the-art applications in materials characterization, bioanalysis and the study of surfaces.

Shedding Light on the Trehalose-Enabled Mucopermeation of Nanoparticles with Label-Free Raman Spectroscopy.

Nanoparticle-based drug delivery systems have attracted significant interest owing to their promise as tunable platforms that offer improved intracellular release of cargo therapeutics. However, significant challenges remain in maintaining the physiological stability of the mucosal matrix due to the nanoparticle-induced reduction in the matrix diffusivity and promotion of mucin aggregation. Such aggregation also adversely impacts the permeability of the nanoparticles, and thus, diminishes the efficacy of nanoparticle-based formulations. Here, an entirely complementary approach is proposed to the existing nanoparticle functionalization methods to address these challenges by using trehalose, a naturally occurring disaccharide that offers exceptional protein stabilization. Plasmon-enhanced Raman spectroscopy and far-red fluorescence emission of the plasmonic silver nanoparticulate clusters are harnessed to create a unique dual-functional, aggregating, and imaging agent that obviates the need of an additional reporter to investigate mucus-nanoparticle interactions. These spectroscopy-based density mapping tools uncover the mechanism of mucus-nanoparticle interactions and establish the protective role of trehalose microenvironment in minimizing the nanoparticle aggregation. Thus, in contrast to the prevailing belief, these results demonstrate that nonfunctionalized nanoparticles may rapidly penetrate through mucus barriers, and by leveraging the bioprotectant attributes of trehalose, an in vivo milieu for efficient mucosal drug delivery can be generated.

(Invited) Solid-Electrolyte Interface and Interphase Depicted By Plasmon-Enhanced Raman Spectroscopy

The growing need for energy storage systems requires batteries with even higher power and energy density with extended life and enhanced safety. This clearly calls for innovations in high energy density electrode materials as well as in design of robust and efficient charge transfer interfaces without electrolyte degradation or chemical side reactions. Charge transport across the solid electrode-liquid electrolyte interface (SLI) is believed to be one of the charge/discharge rate limiting steps. In lithium-ion batteries, the thermodynamic instability of the electrolyte at the SLI leads to formation of a passivation layer, commonly referred to as the solid-electrolyte interphase (SEI). Although the composition, morphology, and structure of SEI in lithium-ion batteries have been extensively studied, probing its evolution in situ at nanoscale is still challenging to a large extent. Plasmon-enhanced Raman spectroscopy (PERS) is promising to solve this challenge. PERS is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity molecules stimulated by incident light. It includes surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The prerequisite of employing PERS to probe the surface molecules is to have a highly ordered plasmonic nanostructured SPR substrate, which is extremely challenging. Large area (cm2) monolayers of gold nanoparticles (Au NPs) have long-range ordered nanogap arrays. The local electromagnetic field is extremely intense within the nanogap (<10 nm) region due to the coupling effect among adjacent nanoparticles, which allows for probing the molecules at immediate vicinity of SLI (distance from the solid surface is of 17 nm). 1 The Au NP monolayers exhibit high SERS sensitivity even down to single-molecule level (enhancement factor > 107). This allows for probing a broad range of trace electrolyte components, such as lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), ethylene carbonate (EC) and diethyl carbonate (DEC), etc. The investigation of a commercial lithium-ion battery electrolyte (LiPF6 in EC+DEC binary solvents) using SERS allows for the determination of the solvent coordination numbers, which ranges from 2 to 5, in sharp contrast to those calculated from bulk liquid electrolytes by standard confocal Raman and infra-red (IR) spectroscopy from 3 to 6. 2 SERS is promising to probe molecular fingerprints in nanoscale through SLI plane. However, it lacks the nanoscale resolution in sample plane. This makes it extremely hard for getting spatial heterogeneity of the SEI, which can be only on the order of 10 nm. Tip Enhanced Raman Spectroscopy (TERS) combines SERS with atomic force microscopy (AFM), capable of providing the chemical vibrational information and topography of the sample in the nanometer spatial resolution simultaneously. TERS analysis on cycled amorphous (a-Si) indicates that the nanometer scale SEI “islands” are unevenly distributed on the Si anode surface. Even for the same SEI “island”, the composition is different from point to point with inter-point distance smaller than 10 nm. The local chemical information studied by TERS is intrinsically different than that collected from the standard confocal Raman and IR spectroscopy. Acknowledgement This work is supported by the U.S. Department of Energy's Vehicle Technologies Office under the Silicon Electrolyte Interface Stabilization (SEISta) Consortium directed by Anthony Burrell and managed by Brian Cunningham

Probing the Nanoscale Heterogeneity of SEI on Silicon Anode Using Tip Enhanced Raman Spectroscopy (TERS)

The composition, morphology and thickness of solid electrolyte interphase (SEI) on silicon anodes are dictated by multiple factors, ranging from the chemistry of silicon surfaces, electrolyte solution structure and chemical passivation on Si surface. In addition, the SEI constantly evolves, as it is electrochemically lithiated (delithiated) due to the enormous volume changes. SEI on silicon typically is reported to be in the range of tens of nanometers and can be compositionally heterogeneous. Normal vibrational spectroscopy techniques such as confocal micro-Raman and FT-IR are useful, but they only provide chemical information at a relatively bulk scale, typically in micron-distance from the solid surface. This makes it extremely hard for getting information from the real SEI, which can be only on the order of 10 nm. Tip Enhanced Raman Spectroscopy (TERS) combines surface plasmon-enhanced Raman spectroscopy with atomic force microscopy, capable of providing the chemical vibrational information and topography of the sample in the nanometer spatial resolution simultaneously. In this report we demonstrate the first TERS study of SEI on cycled amorphous silicon. Amorphous silicon anode (20 nm in thickness on copper current collector) was cycled in a commercial lithium-ion battery electrolyte (1M LiPF6 in EC:DEC, 1:1 vol). TERS analysis on cycled amorphous silicon sample indicates that the nanometer scale SEI “islands” are unevenly distributed on the Si anode surface. Even for the same SEI “island”, the composition is different from point to point with inter-point distance smaller than 2 nm. Acknowledgment This work is funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy

Erratum: Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials

Erratum: Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials

Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials

Since 2000, there has been an explosion of activity in the field of plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS hotspots — nanoscale regions with a strongly enhanced local electromagnetic field — that allow trace-molecule detection, biomolecule analysis and surface characterization of various materials. In particular, we discuss a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials, which feature a strong local electromagnetic field on the surface of the probe material. Enhancement of surface Raman signals up to five orders of magnitude can be obtained from materials that are weakly SERS active or SERS inactive. We provide a detailed overview of future research directions in the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the broad application prospect for materials science and technology. Assisted by rationally designed novel plasmonic nanostructures, surface-enhanced Raman spectroscopy has presented a new generation of analytical tools (that is, tip-enhanced Raman spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy) with an extremely high surface sensitivity, spatial resolution and broad application for materials science and technology.

An impediment to random walk: trehalose microenvironment drives preferential endocytic uptake of plasmonic nanoparticles.

Developing effective theranostic nanoplex platforms for personalized disease treatment necessitates an understanding of and the ability to control live cell-nanoparticle interactions. However, aggregation of nanoparticles on the cell surface and their subsequent internalization is sparsely understood and adversely impact cellular recognition and viability. Here we report a facile method of precisely modulating the aggregation and uptake for silver nanoparticles without altering their surface geometry or functionalization. Exploiting the stabilization properties of trehalose, our approach enables uptake of nanoparticles while reducing aggregation on cell surface and maintaining cell viability. Electron microscopy reveals the larger utilization of endosomal structures in the trehalose-rich environment compared to the nanoparticles' "free" cytosolic diffusion patterns in the control group. Additionally, in the presence of trehalose, plasmon-enhanced Raman spectroscopy confirms the preservation of the protein structure in the vicinity of the nanoparticles reinforcing the promise of the proposed route for label-free, multiplexed intracellular monitoring.

Quasi-3D plasmonic coupling scheme for near-field optical lithography and imaging.

Near-field optical imaging and lithography rely on achieving both high resolution and efficient coupling. Particularly conventional near-field scanning optical microscopy (NSOM) suffers from the trade-off between resolution and efficiency. Planar plasmonic lens schemes can partially solve this issue utilizing plasmonic resonances, but the performance is not robust over a large range of sample materials. In this work we show a novel quasi-3D plasmonic scheme to focus light into the extreme subwavelength region in the near field with an efficiency orders higher than NSOM. The superb performance comes from the strong coupling between the localized mode with an off-plane E-field component and the sample being processed. Our scheme can efficiently focus light to a spot with a diameter down to 1/20 of its wavelength, and the coupling efficiency can be as high as 10%. Theoretically, we demonstrate that the FWHM of the focus spot can be 7nm with an enhancement of about 800 at the UV region. The focusing performance is constantly good over a large variety of materials and the illumination and collection imaging scheme has been demonstrated by simulation. An example design of this quasi-3D coupling scheme is fabricated and its imaging performance is characterized by the apertureless optical near-field measurement. The high coupling efficiency at extreme subwavelength resolution of this quasi-3D coupling scheme opens the door to many applications, such as optical lithography, nanoscale imaging, heat-assisted magnetic recording, plasmon-enhanced Raman spectroscopy, etc.