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Electrocatalytic CO2 reduction reaction (CO2RR) for CH4 production presents a promising strategy to address carbon neutrality, and the incorporation of a second metal has been proven effective in enhancing catalyst performance. Nevertheless, there remains limited comprehension regarding the fundamental factors responsible for the improved performance. Herein, the critical role of Pd in electrocatalytic CO2 reduction to CH4 on Cu-based catalysts has been revealed at a molecular level using in situ surface-enhanced Raman spectroscopy (SERS). A "borrowing" SERS strategy has been developed by depositing Cu–Pd overlayers on plasmonic Au nanoparticles to achieve the in situ monitoring of the dynamic change of the intermediate during CO2RR. Electrochemical tests demonstrate that Pd incorporation significantly enhances selectivity toward CH4 production, and the Faradaic efficiency (FE) of CH4 is more than two times higher than that for the catalysts without Pd. The key intermediates, including *CO2−, *CO, and *OH, have been directly identified under CO2RR conditions, and their evolution with the electrochemical environments has been determined. It is found that Pd incorporation promotes the activation of both CO2 and H2O molecules and accelerates the formation of abundant active *CO and hydrogen species, thus enhancing the CH4 selectivity. This work offers fundamental insights into the understanding of the molecular mechanism of CO2RR and opens up possibilities for designing more efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

In surface-enhanced Raman scattering (SERS) detection research, the shape, structure, surface modification, and material selection of nanoparticles can significantly impact the SERS intensity. Petal-like gap-enhanced Raman tags (P-GERTs) possess numerous sharp tips and edges, which generate localized electric field enhancements, further amplifying the electric field enhancement effect on neighboring molecules and enhancing the SERS signal. Additionally, the surface of P-GERTs can be modified with functional molecules, enabling their application in the detection of disease biomarkers. Using COVID-19 as an example, the performance of P-GERTs in disease biomarker detection was validated, demonstrating that the signal intensity of this probe can reach 55 times that of regular gold nanoparticles and 36.7 times that of smooth shell gap-enhanced Raman tags (S-GERTs). Furthermore, in combination with magnetically retrievable magnetic bead substrates, the N-protein antigen was specifically detected in a one-step process. N-protein was detected within 15 min using a portable Raman spectrometer. The limit of detection (LOD) for the standard sample was 4.28 pg/mL, and the LOD for the actual throat swab sample system was 25.4 pg/mL. This workflow can be extended to the detection of other biomarkers, making it widely applicable. [ABSTRACT FROM AUTHOR]

A rapid and accurate diagnostic modality is essential to prevent the spread of SARS-CoV-2. In this study, we proposed a SARS-CoV-2 detection sensor based on surface-enhanced Raman scattering (SERS) to achieve rapid and ultrasensitive detection. The sensor utilized spike protein deoxyribonucleic acid aptamers with strong affinity as the recognition entity to achieve high specificity. The spherical cocktail aptamers-gold nanoparticles (SCAP) SERS substrate was used as the base and Au nanoparticles modified with the Raman reporter molecule that resonates with the excitation light and spike protein aptamers were used as the SERS nanoprobe. The SCAP substrate and SERS nanoprobes were used to target and capture the SARS-CoV-2 S protein to form a sandwich structure on the Au film substrate, which can generate ultra-strong "hot spots" to achieve ultrasensitive detection. Analysis of SARS-CoV-2 S protein was performed by monitoring changes in SERS peak intensity on a SCAP SERS substrate-based detection platform. This assay detects S protein with a LOD of less than 0.7 fg mL−1 and pseudovirus as low as 0.8 TU mL−1 in about 12 min. The results of the simulated oropharyngeal swab system in this study indicated the possibility of it being used for clinical detection, providing a potential option for rapid and accurate diagnosis and more effective control of SARS-CoV-2 transmission. [ABSTRACT FROM AUTHOR]

Highlights: In situ Raman spectroscopy study of the cation regulation for interfacial water on Au@Pd core–shell nanoparticle surface during hydrogen evolution reaction process. Direct spectral evidence reveals new strategies to optimize the structure of interfacial water by the adjusting of radius and valence of the cation in the electrolyte. The optimized structure of interfacial water will improve the charge transfer efficiency between the water and electrode increasing the performance of the hydrogen evolution reaction. Interfacial water molecules are the most important participants in the hydrogen evolution reaction (HER). Hence, understanding the behavior and role that interfacial water plays will ultimately reveal the HER mechanism. Unfortunately, investigating interfacial water is extremely challenging owing to the interference caused by bulk water molecules and complexity of the interfacial environment. Here, the behaviors of interfacial water in different cationic electrolytes on Pd surfaces were investigated by the electrochemistry, in situ core–shell nanostructure enhanced Raman spectroscopy and theoretical simulation techniques. Direct spectral evidence reveals a red shift in the frequency and a decrease in the intensity of interfacial water as the potential is shifted in the positively direction. When comparing the different cation electrolyte systems at a given potential, the frequency of the interfacial water peak increases in the specified order: Li+ < Na+ < K+ < Ca2+ < Sr2+. The structure of interfacial water was optimized by adjusting the radius, valence, and concentration of cation to form the two-H down structure. This unique interfacial water structure will improve the charge transfer efficiency between the water and electrode further enhancing the HER performance. Therefore, local cation tuning strategies can be used to improve the HER performance by optimizing the interfacial water structure. [ABSTRACT FROM AUTHOR]

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. The solid-electrolyte interphase is crucial for most batteries, but its characterization is challenging. Here, authors develop a depth-sensitive plasmon-enhanced Raman spectroscopy method to enable in-situ and nondestructive resolving of its structure and chemistry as well as formation mechanisms. [ABSTRACT FROM AUTHOR]

Abuse of dopings is one of the serious issues affecting competitive sports globally. Traditional means of analysis for doping detection face the challenges of costly, bulky, and complicated pretreatment, as well as long detection times. Therefore, it is critical to achieve on-site and rapid detection for dopings. Herein, we proposed a strategy for ultrasensitive and quick detection of multiple dopings using a combination of liquid phase extraction and surface-enhanced Raman spectroscopy. The clenbuterol, methadone, oxycodone, and chlordiazepoxide were four dopings, which could be detected conveniently in human saliva and urine using the above approach. The limit of detection for clenbuterol, methadone, oxycodone, and chlordiazepoxide in saliva were 25, 10, 50, and 25 ng/mL, respectively, and in urine, 25, 5, 50, and 25 ng/mL. Finally, in about a minute, four dopings at concentration of 100 ng/mL in saliva and urine can be detected accurately and synchronously. This synchronous detection strategy further demonstrates the enormous advantages of SERS in on-site and rapid detection of multiple drugs. [ABSTRACT FROM AUTHOR]

The problem of excessive quinolone antibiotic residues in pork has stimulated great attention from the international community. However, due to the diversity and structural similarity of quinolone antibiotics, it is difficult to perform multi‐residue rapid detection at the same time. Currently, antibiotic multi‐residue detection methods include ultra‐performance liquid chromatography (UPLC) and colloidal gold immunochromatography. However, it cannot be widely used in on‐site rapid detection due to its shortcomings such as the need for high cost and low sensitivity. Herein, we report the use of surface‐enhanced Raman spectroscopy (SERS) technology for the study of similar structures of quinolone antibiotics. A method for whole class control and rapid quantitative detection of all quinolone antibiotics in pork was established. By using the above method, the detection limit of single standard quinolone antibiotics was 10 μg L−1, and the detection limit of the mixed standard was 1 μg L−1, meeting the international requirements for the detection limit of quinolone antibiotics in pork. At last, by adding a variety of quinolone antibiotics to pork, the real detection set‐up was simulated. The recovery of standard addition was 86.6%–95.3%, and the whole class control method has been well applied, which is of great significance for the detection of pork quinolone antibiotics. Compared with colloidal gold immunochromatography, our method has 2.5 times the detection speed, 1/60 times the cost, and can be quantitatively detected. The method is simple, economical, and efficient and has great application value with broad application prospects in the field of rapid detection of pork antibiotics in the future. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Surface‐enhanced Raman spectroscopy (SERS) has advanced significantly since its inception. Numerous experimental and theoretical efforts have been made to understand the SERS effect and demonstrate its potential. Due to its extremely high sensitivity and selectivity and ability to provide molecular fingerprint information, SERS has a wide range of applications in surface and interfacial chemistry, energy, materials, biomedicine, environmental analysis, etc. This review aims to provide readers with an understanding of the principles, methodologies, and applications of SERS. We briefly introduce the fundamental theory of the SERS enhancement mechanism and summarize the details of the preparation of SERS‐active substrates. Recent applications of SERS in energy systems are then highlighted, including probing surface reactions and interfacial charge transfer of batteries and electrocatalysts. Finally, the challenges and prospects of SERS research are discussed. [ABSTRACT FROM AUTHOR]

The use of imaging technologies has been critical in deciphering biological phenomena, structures, and mechanisms across a wide range of spatial scales. The spatial resolution of traditional imaging modalities cannot meet the needs of high-precision research and diagnosis in biomedical fields. Plasmon resonance is the light–matter interaction that allows localizing far-field radiation in the near field with an intense electromagnetic field, enhancing the nanometric ablation, elastic/inelastic scattering of the adsorbate, and photoluminescence of the fluorophore nearby. Further, plasmon resonance scattering of nanoparticles can sensitively indicate the local environmental changes. This is accomplished by combining the spatially resolved capability with molecular spectrometry techniques such as Raman, infrared, fluorescence, etc., leading to a series of excellent imaging techniques to interrogate diverse biological processes from the tissue to subcellular level. In this tutorial review, we first provide the fundamental aspects of plasmonics. Then we give a systematic discussion of the working principle of these plasmon-based imaging techniques with an emphasis on the achievable spatial resolutions: surface-enhanced Raman spectroscopy (micrometre to nanometre), tip-enhanced ablation and ionization mass spectrometry (submicrometre), scattering-type scanning near-field optical microscopy (nanometre), tip-enhanced Raman spectroscopy (nanometre), tip-enhanced fluorescence spectroscopy (nanometre), and plasmon/molecular ruler microscopy (nanometre to angstrom). We also review the recent developments of the bioimaging applications of these techniques and expect that the plasmon-based techniques will not only pave a new way to decipher mysteries in life sciences but also hold great potential to be extended from fundamental research studies to real-life biomedical applications. [ABSTRACT FROM AUTHOR]

Organophosphorus (OPs) compounds have received enormous attention due to high neurotoxicity. However, the complex detection environment makes it very difficult to detect the OPs compounds at extremely low‐concentration. Therefore, it is vital to develop a high sensitive analytical method for the detection of low‐concentration OPs compounds at complex environment. Here, we proposed a novel surface‐enhanced Raman scattering (SERS) substrate based on the core‐shell structure Au@ZrO2 for the detection of extremely low‐concentration OPs compounds. By using above SERS substrate, we tested different kinds of OPs compounds and obtained excellent detection results. The detection limit of methyl parathion and triazophos can reach 0.01 mg/kg. Meanwhile, under the actual system (orange peel), the detection limit of the methyl parathion and triazophos also can reach 0.5 and 0.1 mg/kg, respectively. In addition, the above substrate is also very effective for the detection of dimethyl methylphosphonate (DMMP), a simulant for the chemical warfare agent (sarin), and the detection limit can reach 100 mg/kg. Besides, we also verified the reproducibility and stability of Au@ZrO2, which showed excellent properties. The relative standard deviation (RSD) of the SERS signal intensity for 20 tests was 6.38% and the enhancement ability of Au@ZrO2 can remain stable within 30 days. These results show that the proposed Au@ZrO2 SERS substrate has great potential in the detection of OPs compounds at extremely low‐concentration in the complex detection environment. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Core‐shell nanostructures constituted by a plasmonic core and an ultrathin shell have drawn enormous attentions in enhanced spectroscopies, catalysis, energy, and other fields because of their splendid properties such as multifunctionality, stability, and adjustability. In this article, we summarized the endeavors made by our group in the past decade about the core‐shell nanostructures in the shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) and plasmon‐enhanced spectroscopies. Meanwhile, the potential challenges and perspectives about core‐shell nanostructures in spectroscopies have also been proposed. Thus, we believe this article would provide an avenue for a comprehensive understanding of enhanced spectroscopies with core‐shell nanostructures. What is the most favorite and original chemistry developed in your research group?? Core‐shell nanostructure enhanced Raman spectroscopy for surface analysis. How do you get into this specific field? Could you please share some experiences with our readers?? I started the studies on Raman spectroscopy since I was a Ph.D. candidate. I think most researchers should concentrate on specific fields, especially those that can hardly be solved by others, and make constant research on them. How do you supervise your students?? First, give highly challenging or unique topics to students. Then, make detailed plans for them and supervise them to execute the plans. What is the most important personality for scientific research?? Insistence and diligence. What are your hobbies? What's your favorite book(s)? Playing computer games. My favorite book is State of Divinity (笑傲江湖), by Louis Cha. What is your favorite journal(s)? The journals report systematic and pioneer works on chemistry, materials, or energy, etc. [ABSTRACT FROM AUTHOR]

Plasmonic metals under photoexcitation can generate energetic hot electrons to directly induce chemical reactions. However, the capability and fundamental insights of the transportation of these hot electrons at plasmonic metal‐2D material interfaces remain unclear. Herein, hot‐electron transfer at Au‐graphene interfaces has been in situ studied using surface‐enhanced Raman spectroscopy (SERS) with atomic layer accuracy. Combining in situ SERS studies with density functional theory calculations, it is proved that hot electrons can be injected from plasmonic Au nanoparticles to graphene and directly penetrate graphene to trigger photocatalytic reactions. With increasing graphene layers, the transportation of hot electrons decays rapidly and would be completely blocked after five layers of graphene. Moreover, the transfer of hot electrons can be modulated by applying an external electric field, and the hot‐electron transfer efficiency under electrochemical conditions is improved by over three times in the presence of a monolayer of graphene. [ABSTRACT FROM AUTHOR]

Developing advanced characterization techniques for single‐atom catalysts (SACs) is of great significance to identify their structural and catalytic properties. Raman spectroscopy can provide molecular structure information, and thus, the technique is a promising tool for catalysis. However, its application in SACs remains a great challenge because of its low sensitivity. We develop a highly sensitive strategy that achieves the characterization of the structure of SACs and in situ monitoring of the catalytic reaction processes on them by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) for the first time. Using the strategy, Pd SACs on different supports were identified by Raman spectroscopy and the nucleation process of Pd species from single atoms to nanoparticles was revealed. Moreover, the catalytic reaction processes of the hydrogenation of nitro compounds on Pd SACs were monitored in situ, and molecular insights were obtained to uncover the unique catalytic properties of SACs. This work provides a new spectroscopic tool for the in situ study of SACs, especially at solid–liquid interfaces. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) is a non‐destructive, highly sensitive, and rapid analytical tool, which has been widely used in different fields, especially for trace quantities of analyte. However, using SERS for reliable quantitative sample analysis is still a great challenge. Herein, a new approach to quantitative SERS analysis at nanostructured substrates that does not require an internal standard or well‐ordered nanostructured SERS substrates is developed. This method is based on the kinetics of chemisorption, that is, on a homogeneous surface, the time taken for adsorption of an adsorbate (adenine or melamine) to reach equilibrium negatively correlates with the concentration of the adsorbate. Quantitative analysis is achieved by using in situ SERS to acquire the adsorption profile of the adsorbate and enabling the adsorption equilibrium time to be calculated. There is excellent correlation between the adenine and melamine SERS response over adsorption equilibrium time with concentration, and the correlation coefficients are 0.9906 and 0.9682, respectively. Moreover, milk sample spiked with the melamine is also studied, and the standard recovery rate is 106%. This work demonstrates a novel, non‐destructive, and cost‐effective quantitative SERS detection technique, which can broaden applications across multiple fields. [ABSTRACT FROM AUTHOR]

Elucidating hydrogen oxidation reaction (HOR) mechanisms in alkaline conditions is vital for understanding and improving the efficiency of anion‐exchange‐membrane fuel cells. However, uncertainty remains around the alkaline HOR mechanism owing to a lack of direct in situ evidence of intermediates. In this study, in situ electrochemical surface‐enhanced Raman spectroscopy (SERS) and DFT were used to study HOR processes on PtNi alloy and Pt surfaces, respectively. Spectroscopic evidence indicates that adsorbed hydroxy species (OHad) were directly involved in HOR processes in alkaline conditions on the PtNi alloy surface. However, OHad species were not observed on the Pt surface during the HOR. We show that Ni doping promoted hydroxy adsorption on the platinum‐alloy catalytic surface, improving the HOR activity. DFT calculations also suggest that the free energy was decreased by hydroxy adsorption. Consequently, tuning OH adsorption by designing bifunctional catalysts is an efficient method for promoting HOR activity. [ABSTRACT FROM AUTHOR]

Starting with a short biography, Schatz then reviews Van Duyne's leading contributions to the discovery and development of SERS as well as pioneering work on localized surface plasmon resonance (LSPR), tip-enhanced Raman scattering (TERS), electrochemical surface-enhanced Raman scattering (SERS)/TERS, and ultrafast nonlinear techniques. SP [ sp 1 SP ] sp The second paper by Moskovits and Piorek is also important, giving a brief history of SERS and its connection with localized surface plasmon excitation. The resulting particle-tipped needles allow dual enhancement of the Raman signals from microdroplets of low concentration analytes by combining analyte enrichment through solvent evaporation and plasmonic SERS enhancement. They discuss the challenges and perspectives in designing and synthesizing nanogap structures that deliver strong, reproducible, and reliable SERS signals for quantitative SERS analysis. SP [ sp 11 SP ] sp In the work presented by Xu, Bell, et al., a SERS-active superhydrophobic (SHP) tip is constructed by an adsorbing a layer of densely packed and uniform plasmonic nanoparticles onto a hydrophilic tip. Also, by utilizing the LRSP mode, electrochemical reactions on the Pt surface could be protected from any nanoscale effects, which is advantageous over conventional SERS. SP [ sp 16 SP ] sp Murakoshi et al. carry out electrochemical SERS measurements to clarify the detailed molecular behavior in the strong coupling regime. [Extracted from the article]

Surface‐enhanced Raman spectroscopy (SERS) is a powerful surface analytical technique; however, its lack of material and morphological generality is a longtime limitation. The invention of shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) using silica shell‐encapsulated Au nanoparticles (NPs) overcomes these problems. Whereas, it is difficult to obtain a silica shell (less than 1 nm thick) without pinholes for generating extremely high SERS enhancements. Graphene is one of the most promising two‐dimensional materials, which has a single‐atom layer thickness. Moreover, graphene can provide additional SERS chemical enhancement. Herein, we prepared graphene‐coated Au (Au@G) NPs via chemical vapor deposition (CVD). The graphene shell thickness could be controlled from a few layers to multilayers, and the Au@G SERS activities were characterized using mercaptobenzoic acid (MBA) as a probe molecule. Both the pH and high‐temperature stabilities of the Au@G nanoparticles were characterized. Also, Pt‐on‐Au@G satellite structures were developed via a self‐assembly method. Whereby Au@G nanoparticles were coated with Pt nanocatalysts, and this bifunctional SERS substrate could be used to monitor in situ catalytic reaction mechanisms occurring on the Pt surface. [ABSTRACT FROM AUTHOR]

Understanding the structure‐activity relationship of catalytic reactions at a molecular level still remains a great challenge. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) is employed to in‐situ study the catalytic hydrogenation of para‐nitrothiophenol (pNTP) on Pt‐based nanocatalysts with different size and composition. The nanocatalysts are assembled on pinhole‐free shell‐isolate nanoparticles (SHINs), which work as Raman amplifiers to enhance the Raman signals of species on the catalysts, allowing the in‐situ monitoring of catalytic reactions carried out on the catalysts. Using this strategy, we find that the catalytic activity of the Pt nanocatalysts shows a volcanic trend with the Pt size, and that PtM (M=Ni or Cu) bimetallic nanocatalysts display much higher performance compared with Pt due to better activation of the nitro group. This work demonstrates that SHINERS is a promising technique for in‐situ study of nanocatalysis thus can deepen the understanding of the behaviors of different catalysts. [ABSTRACT FROM AUTHOR]

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt3Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt3Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt3Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes. [ABSTRACT FROM AUTHOR]

A gap-mode configuration was developed for the in situ SERS study of the structure–activity relationship of Au@Pd core–shell nanocatalysts, which show much better performance in the selective oxidation of benzyl alcohol compared to Pd. The in situ SERS results reveal that the tensile strain in the Pd shell could promote the activation of oxygen, thus improving the activity. Such a tensile strain effect decreases with the increase of the Pd shell thickness, leading to a volcano correlation between the activity and the shell thickness. [ABSTRACT FROM AUTHOR]

Herein, surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) has been successfully applied in the evaluation of cigarette flavoring quality using monolayer films of Au nanoparticles as substrates. With such a method, even a slight difference in the formula of the essence that cannot be directly identified by SERS can be distinguished. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative analysis is a significant step forward for expanding the applications of surface‐enhanced Raman spectroscopy (SERS) in various fields. The reproducibility of the SERS measurement relies on the quality of the SERS substrates. Therefore, high enhancement SERS substrate with high uniformity and reproducibility is highly demanded for quantitative analysis. However, it remains a challenge to realize all the requirements of the SERS substrate. Here, we report 2 types (solution and solid) of SERS substrates with built‐in calibration for quantitative analysis. To prepare the substrates, high monodisperse Au@Ag nanocuboids (NCs) with internal standards trapped between the Au core and Ag shell are synthesized through the Au‐nanorod‐mediated method. It is demonstrated that at least 2 types of SERS tags can be trapped to synthesize the core‐internal standard‐shell (CISS) NCs. The SERS quantitative ability of the CISS NCs in solution is proved by detecting Rhodamine 6G, where a good linear relationship in a wide concentration range from 3 × 10−11 M to 1 × 10−8 M is achieved through the built‐in calibration. Besides the solution‐SERS substrate, CISS NCs are self‐assembled at the air–water interface to form uniform monolayer as the solid SERS substrate. SERS mapping reveals that the uniformity of the enhancement is improved through the built‐in calibration. The quantitative detection of concentration of Rhodamine 6G is achieved through the calibrated SERS mapping of the substrate. The internal and external enhancement factor calculation of the 2 types of SERS substrates indicates the promising method to further improve the reliability of the SERS analysis. [ABSTRACT FROM AUTHOR]

In this feature article, we discuss in detail developmental bottleneck issues in Raman spectroscopy in its early stages and surface-enhanced Raman spectroscopy (SERS) in the past four decades. We divide SERS research into two different directions with different targets. Fundamental research is extending the limits of SERS to single-molecule, sub-nanometer resolution and femtosecond processes. In contrast, practical research is expanding the range of applications with the aim of providing versatile analytical tools for surface, materials, life, environmental, forensic and food sciences and also commercial instruments for use in daily life. In the second direction there have continually been many complex bottlenecks to be overcome. We attempt to enumerate the key issues in detail and also describe the achievements made to overcome the bottlenecks. In the last, but not least important part, we discuss the remaining bottlenecks and possible strategies for overcoming them to enable SERS to be an even more powerful and versatile technique. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) can provide a fingerprint of molecules with ultrahigh sensitivity, down to the single-molecule level. However, accurate quantitative detection in practical samples using SERS is still a great challenge. Herein, a highly uniform shell-isolated Ag@SiO2 nanoparticle (Ag SHIN) monolayer film was prepared and employed as a substrate for the quantitative determination of melamine in milk samples through shell-isolated nanoparticle-enhanced Raman spectroscopy. The Ag SHIN film exhibits excellent reproducibility, high stability, as well as ultrahigh sensitivity with a limit of detection of 0.03 ppm. A linear relationship between the Raman intensity and the melamine concentration in a wide range (1 ppb to 5 ppm) was obtained. These results demonstrate that the Ag SHIN monolayer film is a promising and reliable substrate for the quantitative SERS analysis of practical samples. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface-enhanced Raman spectroscopy (SERS). However, large-scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed-mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV-Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as-prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785-nm excitation, respectively. Significantly, 150-nm Ag NPs exhibit an enhancement factor exceeding 108 for pyridine (Py) molecules in electrochemical SERS (EC-SERS) measurements. Furthermore, finite-difference time-domain (FDTD) calculation is employed to explain the size-dependent SERS activity. Finally, the potential of the as-prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fully understanding the properties of plasmonic nanocavity would boost the spectral detection technologies based on plasmons. Recent efforts are mainly focused on the light-matter interactions, which greatly facilities the cognition for nano-optics in the hot spot. However, realizing the high spatial resolution of vertical plasmons in the specific plasmonic nanocavity has been elusive to date. Herein, the monolayer graphene-mediated plasmonic nanocavity has been constructed, which proves the nanoscale inhomogeneity of the enhanced electromagnetic field distribution. Via sandwiching the graphene monolayer at various positions insider fixed nanocavity, we also successfully and quantitatively elucidate the spatial-dependent resonance of the cavity plasmon mode with a resonance spectral shifts down to ca. 4.43 Ångstrom/nm. Simultaneously, the experimental results and theoretical calculation illustrate the correlation between the near field and far field in the hot spot, which also provides a novel strategy for manipulating the light-matter interactions at the nanoscale and graphene nano-devices fabrication based on plasmons. The well-defined graphene-mediated plasmonic nanocavity was fabricated, and we have successfully elucidated the spatial-dependent resonance of the cavity plasmon mode with a spatial resolution down to sub-2 nanometer and correlate near and far-field effectively. [Display omitted] • Plasmonic hot spot fabrication and controllable plasmon modes with precise gap spacer. • Monolayer graphene sandwiched in the plasmonic nanocavity serves as a probe to detect the gap-mode plasmons. • The near and far-field responses based on graphene-mediated plasmonic nanocavity are correlated effectively. [ABSTRACT FROM AUTHOR]

Shell-isolated nanoparticles (NPs)-enhanced Raman spectroscopy (SHINERS) can be potentially applied to virtually any substrate type and morphology. How to take a step forward to prepare SHINERS NPs (SHINs) with superior performance is critical for the practical applications of surface-enhanced Raman scattering (SERS) in the breadth and depth. Here, we present a method to obtain 120 nm diameter gold NPs coated with ultrathin silica shells (1-4 nm). The silica shell can be controlled growth through carefully tuning a series of parameters, such as amount of 3-aminopropyl triethoxysilane used, pH, reaction time, and reaction temperature. We compare the enhancement factor of the obtained 120 nm Au with a 4 nm silica shell NPs to the 55 nm Au with a 4 nm silica shell NPs, and the activity of a 120 nm SHINs is nearly 24 times that the 55 nm SHIN from a single particle view. We also compare the enhancement factor of 1 nm silica shell Au@SiO2 NPs with the bare Au NPs. The enhancement factor of 1 nm silica shell Au@SiO2 NPs was found to be about twice that of the bare particles. For a deeper understanding of the source of the giant enhanced electrical field of the 1 nm silica shell Au@SiO2 NPs, we study the plasmonic property of single 1 nm silica shell Au@SiO2 NP on a gold film substrate through correlation of the structure of single NP using SEM with its SPR spectroscopy. We find that the multipolar interaction between the single Au@SiO2 NP and gold film substrate is important for the SERS. Our studies on the performance of 120 nm SHINs and the plasmonic property of these particles can significantly expand the applications of SHINERS technique and improve the understanding of physical nature of SHINs. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Constructing plasmonic hotspots in metal nanostructures is essential for plasmon‐enhanced spectroscopies (PESs), but their application in quantitative analysis is a long‐standing challenge. Herein, highly uniform, reproducible, stable, and sensitive 3D hotspots platform substrates are assembled on hydrophobic silicon wafers using a drop of solution containing silica coated surface plasmon resonance (SPR) active nanoparticles (NPs). Plasmon‐enhanced second harmonic generation (PESHG) and surface‐enhanced Raman scattering (SERS) experimental signals increase sharply with the increase of droplet evaporation time, which is attributed to the rapid increase of 3D hotspots generated by gradual decrease of distance between adjacent NPs. Compared with 3D bare metal NP substrate, 3D metal shell‐isolated nanoparticles (SHINs) substrate demonstrates much more stable PESHG and SERS signals attributing to the protecting SiO2 shells. Besides that, uniform distribution of 3D "hotspots" on the hydrophobic substrate can facilitate the quantitative analysis of an analyte using SERS. Experimental and theoretical results demonstrate that the 3D hotspots platform has the potential to be developed as a plasmon‐enhanced substrate for linear and nonlinear spectroscopies with practical sensing applications. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Surface‐enhanced Raman spectroscopy (SERS) has advanced significantly since its inception. Numerous experimental and theoretical efforts have been made to understand the SERS effect and demonstrate its potential. Due to its extremely high sensitivity and selectivity and ability to provide molecular fingerprint information, SERS has a wide range of applications in surface and interfacial chemistry, energy, materials, biomedicine, environmental analysis, etc. This review aims to provide readers with an understanding of the principles, methodologies, and applications of SERS. We briefly introduce the fundamental theory of the SERS enhancement mechanism and summarize the details of the preparation of SERS‐active substrates. Recent applications of SERS in energy systems are then highlighted, including probing surface reactions and interfacial charge transfer of batteries and electrocatalysts. Finally, the challenges and prospects of SERS research are discussed. [ABSTRACT FROM AUTHOR]

Abnormal levels of uric acid (UA) in urine serve as warning signs for gout and metabolic cardiovascular diseases, necessitating the monitoring of UA levels for early prevention. However, the current analytical methods employed suffer from limitations in terms of inadequate suitability for home-based applications and the requirement of non-invasive procedures. In this approach, creatinine, a metabolite with a constant excretion rate, was incorporated as an endogenous internal standard (e-IS) for calibration, presenting a rapid, pretreatment-free, and accurate strategy for quantitative determination of UA concentrations. By utilizing urine creatinine as an internal reference value to calibrate the signal fluctuation of surface-enhanced Raman spectroscopy (SERS) of UA, the quantitative accuracy can be significantly improved without the need for an external internal standard. Due to the influence of the medium, UA, which carries a negative charge, is selectively adsorbed by Au@Ag nanoparticles functionalized with hexadecyltrimethylammonium chloride (CTAC) in this system. Furthermore, a highly convenient detection method was developed, which eliminates the need for pre-processing and minimizes matrix interference by simple dilution. The method was applied to the urine detection of different volunteers, and the results were highly consistent with those obtained using the UA colorimetric kit (UACK). The detection time of SERS was only 30 s, which is 50 times faster than UACK. This quantitative strategy of using urinary creatinine as an internal standard to correct the SERS intensity of uric acid is also expected to be extended to the quantitative detection needs of other biomarkers in urine. [ABSTRACT FROM AUTHOR]

[Display omitted] • Au@RuO x core–shell nanostructures are fabricated to amplify the Raman signals. • Electroreduction of RuO x is in-situ studied using the borrowing SERS strategy. • Direct evidences of OH intermediate are obtained during RuO x electroreduction. • A two-step molecular pathway is proposed for RuO 2 electroreduction. RuO 2 is one of the most promising catalysts for oxygen evolution reaction (OER), a key reaction in water electrolysis. However, the fundamental insights about the structural evolution of RuO 2 under different electrochemical environments remain unclear. Herein, the molecular reaction pathways of the electroreduction of RuO x in alkaline and neutral conditions are identified using in-situ electrochemical surface-enhanced Raman spectroscopy. Au@RuO 2 core–shell nanostructures are fabricated to amplify the Raman signals of species adsorbed on RuO x surfaces. Using such core–shell nanostructures, direct spectroscopic evidences of OH intermediate during the RuO 2 electroreduction process are obtained, which is further confirmed by D 2 O isotopic substitution experiments. A molecular pathway that RuO 2 is reduced to Ru through a two-step reduction process has been proposed. This work provides insightful information on the structural evolution of RuO x with electrochemical environments. [ABSTRACT FROM AUTHOR]

Here, the fabrication of the Ag nanoparticles loaded one-dimensional anodic aluminum oxide defective photonic crystals (Ag@AAO DPCs) with controllable structure parameters is reported using specially designed periodic pulse anodization and vacuum thermal evaporation techniques. The constructed Ag@AAO DPCs films have ordered distributed nanopore surface, high-quality defect state and tunable photonic band gap, which are ideally suited for the surface-enhanced Raman scatting (SERS) substrates that use local electric field and defect state resonance mechanisms. These sbustrates exhibit excellent SERS performance for rhodamine B (rhB) testing with high sensitivity and reproducibility. In which the logarithmic intensity of Raman signal peak at 1646 cm−1 versus the concentration of rhB presents a linear relationship, and the detection limitation can reach to the order of 10−10 mol/L, the enhancement factor can increase to the order of 105, especially when the defect state energy level position is matched with the incident light. This means that the Ag@AAO DPCs can be used as SERS substrates for the trace detection of organic dye molecules. Compared to the common Ag@AAO substrate, the main reasons for the SERS signal enhancement of the Ag@AAO DPCs are attributed to the synergistic effect of the enhanced local electric field strengthened by the Bragg reflection of PC structure and electron transformation induced by the defect state resonance with the incident light. This would be a promising way for applications for surface enhanced Raman scattering. • Preparation of one-dimensional anodic aluminum oxide defective photonic crystals by pulse anodic technique. • Ag@AAO DPCs synergistically enhances the local electric field strength. • The introduction of defects in the photonic crystal-based SERS substrate further enhances the Raman signal. • The Ag@AAO DPCs SERS substrate enhancement factor reached 105, and detection limit of 10−10 mol/L. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases cause enormous morbidity and mortality worldwide. Excessive blood total homocysteine (tHcy) is an independent risk factor for cardiovascular diseases. Therefore, it is imperative to measure the content of tHcy in human blood. However, the currently available analytical methods have the disadvantages such as being time-consuming and expensive. Herein, we propose a rapid clinical quantification of tHcy in human serum using high-performance Ag Nanopolyhedra (Ag NPOLY) as surface-enhanced Raman spectroscopy (SERS) substrates. Generally, 80% of homocysteine (Hcy) in serum is oxidized, and only 20% of Hcy is free. To understand this behavior, we explored the reduction effect of tris(2-carboxyethyl) phosphine (TCEP) on serum Hcy at different pH. The results confirmed that our method can detect 2 µM of Hcy in human serum. As a proof-of-concept, the developed method was applied to the actual clinical detection of human serum tHcy, and the serum of 5 hyperhomocysteinemia (HHcy) patients was verified. Moreover, the obtained, results were consistent with high-performance liquid chromatography (HPLC) results. The linear correlation coefficient of the two methods was 0.9766. Importantly, our analysis can be completed within 15 min, while HCLP requires more than 1 h. Overall, we have successfully developed a rapid SERS-based quantitative method for human serum tHcy, which can provide a new solution for the clinical diagnosis of cardiovascular diseases in the future. [Display omitted] • Constructed a high-performance Ag NPOLY for the detection of tHcy in human serum. • The detection limit for Hcy is 1 µM. • Discussed the optimal condition of TCEP for Hcy reduction. • This method allows the clinical quantification of tHcy. [ABSTRACT FROM AUTHOR]

Dioxin is a highly toxic and carcinogenic pollutant created during industrial production and waste incineration. Pollutant monitoring has made extensive use of surface-enhanced Raman spectroscopy (SERS) as a quick, non-destructive, sensitive, and affordable analytical method. However, the fabrication of a SERS substrate with ultrahigh sensitivity is a challenging task, the detection cost is expensive. Currently, these are the challenges faced by SERS technique for the detection of dioxin pollutants. In this paper, we present Au nanocakes (Au NCs) as an easy-to-build SERS substrate for sensitive SERS detection of dioxins in real samples. Based on three-dimensional finite-difference time-domain (3D-FDTD) calculations, the enhancement factor of the substrate following aggregation is approximately 1010. Using a portable Raman spectrometer, the limit of detection for dioxins such as 1-chloro-dibenzo-p-dioxin (1-CDD), 2,8-dichloro-dibenzo-p-dioxin (2,8-DCDD), and 2,3,7-trichloro-dibenzo-p-dioxin (2,3,7-TrCDD) in clean water reached as low as 5, 5, and 10 ng/mL, respectively. As a real-world application, the same toxic pollutants were detected in sewage water samples. Our findings could lead to the development of novel SERS-based sensors for the rapid detection of dioxins in real-world scenarios. Moreover, a portable Raman spectrometer is used to detect the pollutants, which is easy to use and inexpensive. [Display omitted] • Ultra-sensitive Au nanocake was constructed for detection of dioxins in water. • This facile approach provides a stable platform for field-based analysis. • All experimental data were measured by a portable Raman spectrometer with a detection limit of 5 ppb. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO 2 nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems. [ABSTRACT FROM AUTHOR]

The disaster and devastation from abuse of Methamphetamine (MAMP) have a serious impact on people's mental and physical health. Developing a rapid and accurate method to screen drug suspects and thus control MAMP abuse is essential to social security. Hair analysis for MAMP detection is considered to be one of the most potential methods for monitoring drug abuse due to its convenient sample collection, easy for storage and long traceability period. However, the current accurate detection of MAMP in hair primarily utilizes hyphenated mass spectrometry (MS) techniques, but it is not suitable for field-based detection due to the bulky instrument. Hence, developing alternative portable detection techniques for rapid on-site detection of MAMP in hair is an urgent problem to be solved. Here, the high-performance Au nanocakes (Au NCs) were constructed as surface-enhanced Raman spectroscopy (SERS) substrates to detect MAMP in hair, realizing 5 min ultrafast and ultrasensitive detection utilizing a portable Raman spectrometer. Experiments and finite-difference time-domain (FDTD) simulations show that Au NCs have stronger enhancement than Au nanospheres (Au NPs), and 0.5 ppb (3.35 × 10−9 M) MAMP standard is stably detected by Au NCs as an enhanced substrate. A strategy of liquid-liquid microextraction was exploited to eliminate the interference of complex matrices in hair. This method exhibited excellent reproducibility and temporal stability across different drug addicts (relative standard deviation was 5.14% within 160 s). Our approach shows great promise in public safety, providing a rapid and accurate method to detect in hair by SERS. An ultra-sensitive Au nanocake as SERS substrate was constructed to field-based detection of methamphetamine in hair within 5 min utilizing a portable Raman spectrometer. [Display omitted] • Ultra-sensitive Au nanocake was constructed for detection of MAMP in hair. • The detection limit for the MAMP standard is 0.5 ppb. • Interferences in hair are eliminated with a liquid-liquid microextraction strategy. • This facile approach provides a stable platform for field-based analysis. [ABSTRACT FROM AUTHOR]

Identification of waste oils is challenging in the field of food safety due to the lack of common markers and straightforward analytical methods. Herein, we developed a novel label-free surface-enhanced Raman spectroscopy (SERS) strategy to identify waste oils using Ag nanoparticles solution (Ag NPs sol.) as a SERS substrate to significantly enhance the Raman signal of capsaicin marker molecule usually contained in the waste oils. The enhanced signal was directly detected by a portable Raman spectrometer with the limit of detection (LOD) of 2.9 μg L−1 within 10 min. Concentration-dependent SERS investigation showed the linear relationship between the SERS signal intensity of the characteristic peaks and the concentrations of capsaicin in the range of 10–2500 μg L−1 and the correlation coefficient was 0.9895. Our findings show the sensitivity, accessibility, and reliability of this method for the rapid identification of waste oils and furthermore for the practical applications in the field of food safety. [Display omitted] • Capsaicin is used as the gold standard for the identification of waste oils. • The procedure was completed within 10 min, showing the great performance waste oils identification. • The concentration-dependent SERS research shows reliable quantitative analysis of capsaicin. • The detection limits of capsaicin in waste oil is down to 2.9 μg/L, 104 lower than reported results. • The method uses portable Raman to achieve rapid identification of waste oil, which has great potential for on-site detection. [ABSTRACT FROM AUTHOR]

The creatinine concentration of human urine is closely related to human kidney health and its rapid, quantitative, and low-cost detection has always been demanded. Herein, a surface-enhanced Raman spectroscopic (SERS) method for rapid and cost-effective quantification of creatinine concentrations in human urine was developed. A Au nanoparticle solution (Au sol) was used as a SERS substrate and the influence of different agglomerating salts on its sensitivity toward detecting creatinine concentrations was studied and optimized, as well as the effect of both the salt and Au sol concentrations. The variation in creatinine spectra over time on different substrates was also examined, demonstrating reproducible quantitative analysis of creatinine concentrations in solution. By adjusting the pH, a simple liquid−liquid solvent extraction procedure, which extracted creatinine from human urine, was used to increase the SERS detection selectivity toward creatinine in complex matrices. The quantitative results were compared to those obtained with a clinically validated enzymatic "creatinine kit (CK)." The limit of detection (LOD) for the SERS technique was 1.45 mg L−1, compared with 3.4 mg L−1 for the CK method. Furthermore, cross-comparing the results from the two methods, the average difference was 5.84% and the whole SERS detection process could be completed within 2 min compared with 11 min for the CK, indicating the practicality of the quantitative SERS technique. This novel quantitative technique shows promises as a high-throughput platform for relevant clinical and forensic analysis. • A highly sensitive SERS technique was developed for the rapid quantification of creatinine levels in human urine. • The SERS detection selectivity was improved through a simple liquid−liquid solvent extraction procedure. • This novel approach promises a high-throughput platform for clinical and forensic analysis. [ABSTRACT FROM AUTHOR]

Here, the preparation of TiO 2 nanotube photonic crystals (PCs) and their periodical Ti3+ self-doping were synchronously accomplished for forming Ti3+-TiO 2 PCs by introducing an appropriate reduction pulse voltage (−4 V) into the periodical anodic oxidation voltage waveform. Subsequently, some Ag nanoparticles were deposited on the surface of the Ti3+-TiO 2 PCs by vacuum evaporation for getting Ag/Ti3+-TiO 2 PCs nanostructures, which were ideally suited for the surface-enhanced Raman scatting (SERS) substrates. Compared to the Ag loaded TiO 2 nanotubes, the SERS signal of the Ag/Ti3+-TiO 2 PCs for RhB can be improved 8.4 times. The desirable SERS property would be attributed to the synergistic effects of the localized electromagnetic (EM) field enhancement and charge-transfer (CT) chemical enhancement mechanisms, which was also discussed in detail. ● Ag/Ti3+-TiO 2 PCs were specially designed and prepared as the SERS substrates. ● The periodical Ti3+ self-doping was synchronously accomplished in anodization process. ● The SERS signal of the Ag/Ti3+-TiO 2 PCs for RhB can be improved 8.4 times. ● The property is attributed to localized field and charge-transfer synergistic enhancement. [ABSTRACT FROM AUTHOR]