Surface analysis using shell-isolated nanoparticle-enhanced Raman spectroscopy

Recent advances of MOF-based SERS substrates in quantitative analysis of food contaminants: a review

Advancements in food-contaminant detection technologies can significantly improve food safety and human health. Surface-enhanced Raman spectroscopy (SERS) has become the preferred analytical method for food-safety detection owing to its numerous advantages, which include unique 'molecular fingerprinting' features, high sensitivity, rapid responses, and non-invasive characteristics. Raman-signal enhancements rely heavily on high-performance SERS substrates. In recent years, metal-organic framework (MOF)-based SERS substrates have gained attention as promising candidates for developing SERS technologies owing to their distinctive structures and functions. This review comprehensively examines recent advances in MOF-based SERS substrates, focusing on the main role of MOFs in SERS substrates as well as their typical categories and structures, construction methods, and representative applications in food-contaminant detection. First, the primary roles of MOFs in SERS substrates are briefly introduced. Next, a comprehensive overview of the typical categories and structures of MOF-based SERS substrates is discussed. Subsequently, a fundamental view of the general construction methods for MOF-based SERS substrates is presented. Next, the main applications of MOF-based SERS substrates for food-contaminant detection are summarised. Finally, challenges and perspectives, including improvements in SERS performance and stability, and the unification of SERS mechanisms, are addressed and discussed.

Osmolyte-Induced Modulation of Hofmeister Series

Natural selection has driven the convergence toward a selected set of osmolytes, endowing them with the necessary efficiency to manage stress arising from salt diversity. This study combines atomistic simulations and experiments to investigate how two osmolytes, glycine and betaine, individually modulate the Hofmeister ion ordering of alkali metal salts (LiCl, KCl, and CsCl) near a charged silica interface. Both osmolytes are found to prevent salt-induced aggregation of the charged entities, yet their mode and degree of relative modulation depend on their intricate interplay with specific salt cations. Betaine's ion-mediated surface interaction maintains Hofmeister ion ordering, whereas glycine alters the relative Hofmeister order of the cation by salt-specific ion desorption from the surface. Experimental validation through surface-enhanced Raman spectroscopy supports these findings, elucidating osmolyte-mediated alterations in interfacial water structures. These observations based on an inorganic interface are reciprocated in amyloid beta 40 dimerization dynamics, highlighting osmolytes' efficacy in mitigating salt-induced aggregation. A molecular analysis suggests that the differential modes of interaction, as found here for glycine and betaine, are prevalent across classes of zwitterionic osmolytes.

Adenosine Triphosphate Inhibits Cold-Responsive Aggregation

Adenosine triphosphate (ATP), ubiquitous in all living organisms, is conventionally recognized as a fundamental energy currency essential for a myriad of cellular processes. While its traditional role in energy metabolism requires only micromolar concentrations, the cellular content of ATP has been found to be significantly higher at the millimolar level. Recent studies have attempted to correlate this higher concentration of ATP with its nonenergetic role in maintaining protein homeostasis, leaving the investigation of ATP's nontrivial activities in biology an open question. Here, by coupling computer simulations and experiments, we uncover new insights into ATP's role as a cryoprotectant against cold-salt stress, highlighting the necessity for higher cellular ATP concentrations. We present direct evidence at charged silica interfaces, demonstrating ATP's ability to restore native intersurface interactions disrupted by combined cold-salt stress, thereby inhibiting cold-responsive aggregation in high-salt conditions. ATP desorbs salt cations from negatively charged surfaces through predominant interactions between ATP and the salt cations. Although the mode of ATP's action remains unchanged with temperature, the extent of interaction scales with temperature, requiring less ATP activity at lower temperatures, justifying the reason for reduction in cellular ATP content due to the cold effect, reported in previous experimental studies. The trend observed in inorganic nanostructures is recurrent and robustly transferable to charged protein interfaces. A thorough comparison of ATP's cryoprotective activity with traditionally known biological cryoprotectants (glycine and betaine) reveals ATP's greater efficiency. In retrospect, our findings highlight ATP's additional biological role in cryopreservation, expanding its potential biomedical applications by offering effective protection of cells from cryoinjuries and avoiding the significant challenges associated with the toxicity of organic cryoprotectants.

Silver microplasma-engineered nanoassemblies on periodic nanostructures for SERS applications

This research aimed to enhance the performance of surface-enhanced Raman scattering (SERS) substrates through the implementation of periodic nanostructures, effectively increasing surface area and uniformity. The approach involved a two-step process: initially, magnetron sputtering was employed to minimize the Raman background signal from the polymer substrate, and subsequently, the microplasma nanoparticle coating method was utilized to augment the presence of silver nanoparticles (AgNPs) for enhancing SERS efficacy. The outcome revealed several key findings: a coefficient of variation (CV) of approximately 8% for individual substrates (3 × 3 cm2), a CV of 6% between different fabrication batches, and a sustained signal strength of 85% over a storage period exceeding two months in a moisture-proof enclosure, thus meeting commercial product standards. Moreover, the substrate demonstrated a limit of detection of 8.4 × 10-7 M (306.5 ppb) for malachite green under non-resonance Raman excitation conditions along with an impressive enhancement factor of 2.69 × 106, establishing it as a high-performance and stable SERS substrate.

Surfactant-Free Method to Prevent Gold Nanoparticle Aggregation and Its Surface-Enhanced Raman Scattering Applications

The introduction of surfactants to stabilize colloidal citrate-reduced gold nanoparticles (prevent aggregation) is usually used in surface-enhanced Raman scattering (SERS) applications. However, the surfactants have many drawbacks for SERS applications, such as increasing the SERS background and blocking surface active sites. Here, we develop a surfactant-free method to stabilize colloidal cit-AuNPs based on alkali regulation, and this method can prevent gold nanoparticle aggregation under different harsh treatments, including ligand modification, centrifugation-based washing/enrichment, and salt addition. The SERS spectra, density functional theory simulation, and ζ potentials of cit-AuNPs indicate that the stability of enhanced cit-AuNPs under alkaline conditions is attributed to both the increased negative charge density (by ∼6 times from pH 7 to 12) and the molecular configuration on the metal surface. Compared with surfactant-based methods, this method can well maintain the inherent optical and interface properties of nanoparticles, avoid the SERS background, and avoid blocking of the surface active site due to the presence of surfactants. This method will enable AuNPs to have a wide range of applications in areas such as highly sensitive SERS sensors.

Potential cycling boosts the electrochemical conversion of polyethylene terephthalate-derived alcohol into valuable chemicals

The electrocatalytic valorization of polyethylene terephthalate-derived ethylene glycol to valuable glycolic acid offers considerable economic and environmental benefits. However, conventional methods face scalability issues due to rapid activity decay of noble metal electrocatalysts. We demonstrate that a dynamic potential cycling approach, which alternates the electrode potential between oxidizing and reducing values, significantly mitigates surface deactivation of noble metals during electrochemical oxidation of ethylene glycol. This method enhances catalyst activity by 20 times compared to a constant-potential approach, maintaining this performance for up to 60 h with minimal deactivation. In situ Raman and X-ray absorption spectroscopy show that this effectiveness results from efficient removal of surface oxide during the reaction. The strategy is applicable to polyethylene terephthalate hydrolysates and various noble metals, such as palladium, gold, and platinum, with palladium showing a high conversion rate in recent studies. Our approach offers an efficient and durable method for electrochemical upcycling of biomass-derived compounds.

A disposable fiber-optic plasmonic sensor for chemical sensing

The integration of fiber optics and plasmonic sensors is promising to improve the practical usability over conventional bulky sensors and systems. To achieve high sensitivity, it typically requires fabrication of well-defined plasmonic nanostructures on optical fibers, which greatly increases the cost and complexity of the sensors. Here, we present a fiber-optic sensor system by using chemical absorption of gold nanoparticles and a replaceable configuration. By functioning gold nanoparticles with aptamers or antibodies, we demonstrate the applications in chemical sensing using two different modes. Measuring shift in resonance wavelength enables the Pb2+ detection with a high linearity and a limit of detection of 0.097nM, and measuring absorption peak amplitude enables the detection of E. coli in urinary tract infection with a dynamic range between 103 to 108 CFU/mL. The high sensitivity, simple fabrication and disposability of this sensing approach could pave the way for point-of-care testing with fiber-optic plasmonic sensors.

Role of Interfacial Water Structure in the Electroreduction of NO over Cu2O

The electrochemical nitric oxide reduction reaction (NORR), which utilizes water as the sole hydrogen source, has the potential to facilitate ammonia production while concurrently mitigating pollutants. However, limited research has been dedicated to characterizing the structure of interfacial water due to the challenges associated with probing this intricate system, impeding the development of more efficient catalysts for the NORR process. Herein, the Cu2O microcrystals with distinct exposed facets, including {100}, {110}, and {111}, are employed for the model catalysts to investigate interfacial water structure and intermediate species in the NORR process. The results from shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) indicated that the NORR performance in 0.1 M Na2SO4 (with heavy water as the solvent) was positively correlated to the proportion of hydrated Na+ ion water. In addition, a sequence of intermediates from the NORR, including *NOH, *NH, *NH2, and *NH3, was detected by employing a combination of multiple in situ characterization methods. Furthermore, in conjunction with experimental results and theoretical calculations, we revealed the potential reaction pathway of NORR. This study offers novel insights into the NORR mechanism and valuable guidance for the design of high-performance catalysts for ammonia production.

Synergistic Modulation of Multiple Sites Boosts Anti-Poisoning Hydrogen Electrooxidation Reaction with Ultrasmall (Pt0.9Rh0.1)3V Ternary Intermetallic Nanoparticles

Promoting the hydrogen oxidation reaction (HOR) activity and poisoning tolerance of electrocatalysts is crucial for the large-scale application of hydrogen-oxygen fuel cell. However, it is severely hindered by the scaling relations among different intermediates. Herein, lattice-contracted Pt-Rh in ultrasmall ternary L12-(Pt0.9Rh0.1)3V intermetallic nanoparticles (~2.2 nm) were fabricated to promote the HOR performances through an oxides self-confined growth strategy. The prepared (Pt0.9Rh0.1)3V displayed 5.5/3.7 times promotion in HOR mass/specific activity than Pt/C in pure H2 and dramatically limited activity attenuation in 1000 ppm CO/H2 mixture. In situ Raman spectra tracked the superior anti-CO* capability as a result of compressive strained Pt, and the adsorption of oxygen-containing species was promoted due to the dual-functional effect. Further assisted by density functional theory calculations, both the adsorption of H* and CO* on (Pt0.9Rh0.1)3V were reduced compared with that of Pt due to lattice contraction, while the adsorption of OH* was enhanced by introducing oxyphilic Rh sites. This work provides an effective tactic to stimulate the electrocatalytic performances by optimizing the adsorption of different intermediates severally.

A Systematic Study of Methyl Carbodithioate Esters as Effective Gold Contact Groups for Single-Molecule Electronics

There are several binding groups used within molecular electronics for anchoring molecules to metal electrodes (e.g., R-SMe, R-NH2, R-CS2 -, R-S-). However, some anchoring groups that bind strongly to electrodes have poor/unknown stability, some have weak electrode coupling, while for some their binding motifs are not well defined. Further binding groups are required to aid molecular design and to achieve a suitable balance in performance across a range of properties. We present an in-depth investigation into the use of carbodithioate esters as contact groups for single-molecule conductance measurements, using scanning tunnelling microscopy break junction measurements (STM-BJ) and detailed surface spectroscopic analysis. We demonstrate that the methyl carbodithioate ester acts as an effective contact for gold electrodes in STM-BJ measurements. Surface enhanced Raman measurements demonstrate that the C=S functionality remains intact when adsorbed on to gold nanoparticles. A gold(I) complex was also synthesised showing a stable C=S→AuI interaction from the ester. Comparison with a benzyl thiomethyl ether demonstrates that the C=S moiety significantly contributes to charge transport in single-molecule junctions. The overall performance of the CS2Me group demonstrates it should be used more extensively and has strong potential for the fabrication of larger area devices with long-term stability.

Damage-Free Silica Coating for Colloidal Nanocrystals Through a Proactively Water-Generating Amidation Reaction at High Temperature

Silica is a promising shell coating material for colloidal nanoparticles due to its excellent chemical inertness and optical transparency. To encapsulate high-quality colloidal nanocrystals with silica shells, the silane coupling hydrolysis is currently the most effective approach. However, this reaction requires water, which often adversely affects the intrinsic physicochemical properties of nanocrystals. Achieving a damage-free silica encapsulation process to nanocrystals by hydrolysis is a huge challenge. Here, a novel strategy is developed to coat colloidal nanocrystals with a denser silica shell via a proactively water-generating reaction at high temperature. In this work, water molecules are continuously and proactively released into the reaction system through the amidation reaction, followed by in situ hydrolysis of silane, completely avoiding the impacts of water on nanocrystals during the silica coating process. In this work, water sensitive perovskite nanocrystals (CsPbBr3) are selected as the typical colloidal nanocrystals for silica coating. Notably, this high-temperature in situ encapsulation technology greatly improves the optical properties of nanocrystals, and the silica shells exhibit a denser structure, providing nanocrystals with better protection. This method overcomes the challenge of the influence of water on nanocrystals during the hydrolysis process, and provides an important reference for the non-destructive encapsulation of colloidal nanocrystals.

Live chicken egg embryos as an alternative in vivo tumour model for deep surface enhanced Raman spectroscopy

Live chicken egg embryos offer new opportunities for evaluation and continuous monitoring of tumour growth for in vivo studies compared to traditional rodent models. Here, we report the first use of surface enhanced Raman scattering (SERS) mapping and surface enhanced spatially offset Raman scattering (SESORS) for the detection and localisation of targeted gold nanoparticles in live chicken egg embryos bearing a glioblastoma tumour.

Interfacial OOH* mediated Fe(II) regeneration on the single atom Co-N-C catalyst for efficient Fenton-like processes

Fe(II) regeneration is decisive for highly efficient H2O2-based Fenton-like processes, but the role of cobalt-containing reactive sites in promoting Fe(II) regeneration was overlooked. Herein, a single atom Co-N-C catalyst was employed in Fe(II)/H2O2 system to promote the degradation of diverse organic contaminants. The EPR and quenching experiments indicated Co-N-C significantly enhanced the generation of superoxide species, and accelerated hydroxyl radical generation for pollutant degradation. The electrochemical and surface composition analyses demonstrated the enhanced H2O2 activation and Fe(III)/Fe(II) recycling on the catalyst. Furthermore, in-situ Raman characterization with shell-isolated gold nanoparticles was employed to visualize the interfacial reactive intermediates and their time-resolved interaction. The accumulation of interfacial CoOOH* was confirmed when Co-N-C activated H2O2 alone, but it rapidly transformed into FeOOH* upon Fe(II) addition. Besides, the temporal variation of OOH* intermediates and the relative intensity of Co(III)-O and Co(IV)=O peaks depicted the dynamic interaction of reactive intermediates along the H2O2 consumption. With this basis, we proposed a mechanism of interfacial OOH* mediated Fe(II) regeneration, which overcame the kinetical limitation of Fe(II)/H2O2 system. Therefore, this study provided a primary effort to elucidate the overlooked role of interfacial CoOOH* in the Fenton-like processes, which may inspire the design of more efficient catalysts.

Alternative nano-lithographic tools for shell-isolated nanoparticle enhanced Raman spectroscopy substrates

Chemically synthesized metal nanoparticles (MNPs) have been widely used as surface-enhanced Raman spectroscopy (SERS) substrates for monitoring catalytic reactions. In some applications, however, the SERS MNPs, besides being plasmonically active, can also be catalytically active and result in Raman signals from undesired side products. The MNPs are typically insulated with a thin (∼3 nm), in principle pin-hole-free shell to prevent this. This approach, which is known as shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), offers many advantages, such as better thermal and chemical stability of the plasmonic nanoparticle. However, having both a high enhancement factor and ensuring that the shell is pin-hole-free is challenging because there is a trade-off between the two when considering the shell thickness. So far in the literature, shell insulation has been successfully applied only to chemically synthesized MNPs. In this work, we alternatively study different combinations of chemical synthesis (bottom-up) and lithographic (top-down) routes to obtain shell-isolated plasmonic nanostructures that offer chemical sensing capabilities. The three approaches we study in this work include (1) chemically synthesized MNPs + chemical shell, (2) lithographic substrate + chemical shell, and (3) lithographic substrate + atomic layer deposition (ALD) shell. We find that ALD allows us to fabricate controllable and reproducible pin-hole-free shells. We showcase the ability to fabricate lithographic SHINER substrates which report an enhancement factor of 7.5 × 103 ± 17% for our gold nanodot substrates coated with a 2.8 nm aluminium oxide shell. Lastly, by introducing a gold etchant solution to our fabricated SHINER substrate, we verified that the shells fabricated with ALD are truly pin-hole-free.

Rapid detection of trace nitrobenzene in water via SERS using a portable Raman spectrometer

Nitrobenzene is currently the most widely used explosive substance, and is known for its high toxicity and mutagenicity. It can cause severe environmental and water pollution, posing a risk to public health. Among various explosives analysis methods, surface-enhanced Raman spectroscopy (SERS) has the advantages of fast analysis speed, low detection cost, and easy operation, and has become one of the most promising analytical detection methods. Here, we present a portable and reliable sol-based SERS method for the detection of trace amounts of 2,4,6-trinitrotoluene (TNT) in different water bodies. The Meisenheimer complex formed by nitrobenzene and hydrazine hydrate can assemble on unmodified Au nanoparticles in a sol via Au-N bonds, enabling rapid detection of TNT in seawater, lake water, and tap water using a portable Raman spectrometer. Experimental results show that this SERS method can complete the detection within a few minutes and the detection sensitivity can reach 0.01 mg L-1, which is far lower than China's national standard of no more than 0.5 mg L-1. Furthermore, this method was also successfully applied to detect trace 2,4-dinitrotoluene (2,4-DNT) and picric acid (2,4,6-trinitrophenol) in water, demonstrating its strong applicability for on-site detection of nitrobenzene explosives.

Selective and Accurate Detection of Nitrate in Aquaculture Water with Surface-Enhanced Raman Scattering (SERS) Using Gold Nanoparticles Decorated with β-Cyclodextrins

A surface-enhanced Raman scattering (SERS) method for measuring nitrate nitrogen in aquaculture water was developed using a substrate of β-cyclodextrin-modified gold nanoparticles (SH-β-CD@AuNPs). Addressing the issues of low sensitivity, narrow linear range, and relatively poor selectivity of single metal nanoparticles in the SERS detection of nitrate nitrogen, we combined metal nanoparticles with cyclodextrin supramolecular compounds to prepare a AuNPs substrate enveloped by cyclodextrin, which exhibits ultra-high selectivity and Raman activity. Subsequently, vanadium(III) chloride was used to convert nitrate ions into nitrite ions. The adsorption mechanism between the reaction product benzotriazole (BTAH) of o-phenylenediamine (OPD) and nitrite ions on the SH-β-CD@AuNPs substrate was studied through SERS, achieving the simultaneous detection of nitrate nitrogen and nitrite nitrogen. The experimental results show that BTAH exhibits distinct SERS characteristic peaks at 1168, 1240, 1375, and 1600 cm-1, with the lowest detection limits of 3.33 × 10-2, 5.84 × 10-2, 2.40 × 10-2, and 1.05 × 10-2 μmol/L, respectively, and a linear range of 0.1-30.0 μmol/L. The proposed method provides an effective tool for the selective and accurate online detection of nitrite and nitrate nitrogen in aquaculture water.

Ultrasensitive and selective detection of sulfamethazine in milk via a Janus-labeled Au nanoparticle-based surface-enhanced Raman scattering-immunochromatographic assay

Sulfamethazine (SM2) is an antibacterial drug，which has been extensively used in human and veterinary medicine, long-term consumption of which may lead to the accumulation of sulfonamides in the body. Detection of sulfonamides often uses microbiological approaches, mass spectrometry and chromatography, which are expensive and time-consuming. Surface-enhanced Raman scattering-based immunochromatographic assay (SERS-ICA) has been recently applied in the detection. Herein, a Janus-labeled Au nanoparticle with subnanosized SiO2-monoclonal antibody and SERS reporter (DTNB) modified simultaneously (mAbAuNpDTNB) has been developed in a SERS-based lateral flow immunosensor, which can be used for rapid, quantitative and ultrasensitive detection of sulfamethazine residue in milk. The mAbAuNpDTNB exhibits a specific array on a paper stripe, which not only identifies sulfamethazine but also straightforwardly exposes the Raman reporter between the AuNps via self-assembly. The detection sensitivity of SERS-ICA for sulfamethazine reached 0.1 pg/mL, which was far below the previously published value by ELISA and the maximum residue limit set by the European Union. The entire SERS-ICA detection for sulfamethazine was completed within 15 min. Furthermore, high accuracy for this assay was exhibited in the spiking experiment with a recovery percentage of 88.1%-112.7%. The results demonstrated that this SERS-ICA can potentially be applied in point-of-care testing as an ultrasensitive and quantitative to semi-quantitative analytical method.

Plasmonic and Photothermal Properties of Silica-Capped Gold Nanoparticle Aggregates

Owing to their biocompatibility, gold nanoparticles have many applications in healthcare, notably for targeted drug delivery and the photothermal therapy of tumors. The addition of a silica shell to the nanoparticles can help to minimize the aggregation of the nanoparticles upon exposure to harsh environments and protect any Raman reporters adsorbed onto the metal surface. Here, we report the effects of the addition of a silica shell on the photothermal properties of a series of gold nanostructures, including gold nanoparticle aggregates. The presence of a Raman reporter at the surface of the gold nanoparticles also allows the structures to be evaluated by surface-enhanced Raman scattering (SERS). In this work, we explore the relationship between the degree of aggregation and the position and the extinction of the near-infrared plasmon on the observed SERS intensity and in the increase in bulk temperature upon near-infrared excitation. By tailoring the concentration of the silane and the thickness of the silica shell, it is possible to improve the photothermal heating capabilities of the structures without sacrificing the SERS intensity or changing the optical properties of the gold nanoparticle aggregates.

Surface-enhanced fluorescence for lipopolysaccharide analysis based on shell-isolated nanoparticle

Lipopolysaccharide (LPS) as the component of cell membrane on gram-negative bacteria played a central role on inflammatory inducer to stimulate a multi-system host response. Herein, a surface-enhanced fluorescent (SEF) sensor was developed for LPS analysis based on shell-isolated nanoparticles (SHINs). The fluorescent signal of CdTe quantum dots (QDs) was amplified by silica shell-coated Au nanoparticles (Au NPs). The 3D finite-difference time-domain (3D-FDTD) simulation revealed that this enhancement was due to local electric field amplification. This method has a linear detection range of 0.1-20 μg/mL and a detection limit of 64 ng/mL for LPS. Furthermore, the developed method was successfully applied for LPS analysis in milk and human serum sample. The results indicated that the as-prepared sensor has significant potential for selective detection of LPS in biomedical diagnosis and food safety.

Fabrication of Ag nanostar and PEI-based SERS substrate for sensitive and rapid detection of SO2: Application for detection of sulfite residues in beer

Because of sulfite's potential toxicity, there is a growing concern about detecting and controlling its concentration in foods, alcoholic beverages, pharmaceuticals, and environmental samples to ensure public health. A branched polyethyleneimine-coated silver nano-star (AgNS@PEI) surface-enhanced Raman scattering (SERS) substrate was synthesized in this study for use as a sensitive, simple, rapid, stable, and reproducible non-destructible sulfite detection analytical technique. The seed morphology of the nano-star was created by using hydroxylamine (NH2OH) solution as a primary reducing agent, followed by a slow secondary reduction by trisodium citrate dihydrate (HOC(COONa)(CH2COONa)2 2H2O), resulting in the complete growth of the silver nano-star. For extra stability and selective absorption of sulfur dioxide from the headspace extraction of SO2 from sulfites, the nano-stars were thin coated with branched polyethyleneimine (b-PEI). The results showed that the thin-coated plasmonic substrates selectively absorb sulfur dioxide molecules, allowing sulfites in beer samples to be detected with a detection limit of 0.48 mg/L. Furthermore, the PEI-coated silver nano-star demonstrated increased stability and reproducibility, allowing for longer use of the substrate. Recovery experiments with recovery rates ranging from 95 to 112% and relative standard deviations ranging from 1.55 to 8.1% demonstrated that headspace extraction, selective SO2 absorption by the synthesized substrate, and subsequent SERS detections were reliable and valid for practical applications. Finally, this study developed an SO2-sensitive, selective, and robust Si@AgNS@PEI substrate for effective SERS detection and monitoring of sulfite levels in real-world environmental samples.

Rapidly determining the 3D structure of proteins by surface-enhanced Raman spectroscopy

Despite great advances in protein structure analysis, label-free and ultrasensitive methods to obtain the natural and dynamic three-dimensional (3D) structures are still urgently needed. Surface-enhanced Raman spectroscopy (SERS) can be a good candidate, whereas the complexity originated from the interactions between the protein and the gradient surface electric field makes it extremely challenging to determine the protein structure. Here, we propose a deciphering strategy for accurate determination of 3D protein structure from experimental SERS spectra in seconds by simply summing SERS spectra of isolated amino acids in electric fields of different strength with their orientations in protein. The 3D protein structure can be reconstructed by comparing the experimental spectra obtained in a well-defined gap-mode SERS configuration with the simulated spectra. The gradient electric field endows SERS with a unique advantage to section biomolecules with atomic precision, which makes SERS a competent tool for monitoring biomolecular events under physiological conditions.

Molecular-Cling-Effect of Fluoroethylene Carbonate Characterized via Ethoxy(pentafluoro)cyclotriphosphazene on SiOx/C Anode Materials - A New Perspective for Formerly Sub-Sufficient SEI Forming Additive Compounds

Effective electrolyte compositions are of primary importance in raising the performance of lithium-ion batteries (LIBs). Recently, fluorinated cyclic phosphazenes in combination with fluoroethylene carbonate (FEC) have been introduced as promising electrolyte additives, which can decompose to form an effective dense, uniform, and thin protective layer on the surface of electrodes. Although the basic electrochemical aspects of cyclic fluorinated phosphazenes combined with FEC were introduced, it is still unclear how these two compounds interact constructively during operation. This study investigates the complementary effect of FEC and ethoxy(pentafluoro)cyclotriphosphazene (EtPFPN) in aprotic organic electrolyte in LiNi0.5 Co0.2 Mn0.3 O ∥ SiOx /C full cells. The formation mechanism of lithium ethyl methyl carbonate (LEMC)-EtPFPN interphasial intermediate products and the reaction mechanism of lithium alkoxide with EtPFPN are proposed and supported by Density Functional Theory calculations. A novel property of FEC is also discussed here, called molecular-cling-effect (MCE). To the best knowledge, the MCE has not been reported in the literature, although FEC belongs to one of the most investigated electrolyte additives. The beneficial MCE of FEC toward the sub-sufficient solid-electrolyte interphase forming additive compound EtPFPN is investigated via gas chromatography-mass spectrometry, gas chromatography high resolution-accurate mass spectrometry, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy, and scanning electron microscopy.

Molybdenum disulfide-loaded multilayer AuNPs with colorimetric-SERS dual-signal enhancement activities for flexible immunochromatographic diagnosis of monkeypox virus

The sudden outbreak of monkeypox in 2022 suggests the importance of developing a rapid but sensitive virus detection technology. Herein, we report a colorimetric/surface-enhanced Raman scattering (SERS) dual-signal co-enhanced immunochromatographic assay (ICA) for the flexible, ultrasensitive, and accurate detection of monkeypox virus (MPXV) in various complex samples. A thickness-controlled polyethyleneimine interlayer (1 nm) is coated onto two-dimensional molybdenum disulfide (MoS2) nanosheet to enable the electrostatic adsorption of two layers of dense 30 nm AuNPs, which not only improves colorimetric ability but also creates numerous efficient SERS hotspots. Moreover, the SERS activity of film-like dual-signal tag (MoS2@Au-Au) is drastically enhanced by combining the chemical enhancement effect of MoS2 sheets and the electromagnetic enhancement effect of Au-Au hotspots. The introduction of MoS2@Au-Au greatly broadens the application range of existing ICA methods, in which the colorimetric signal supports the quick identification of the target virus and the SERS signal allows the quantitative detection of MPXV with detection limits of as low as 0.2 and 0.002 ng/mL. Given its rapid detection ability (< 20 min), high accuracy in real samples (RSD < 9.89 %), and superior sensitivity than traditional AuNP-based colorimetric ICA (> 500 times), the proposed assay has great potential for field application.

Ti3C2Tx MXene -facilitated non-selective trapping effect: Efficient SERS detection of exosomal PD-L1

Biosensors developed through a sandwich approach have demonstrated favorable detection performance for exosomal programmed cell death 1 ligand 1 (ExoPD-L1) detection. However, the reported PD-L1 antibodies, peptides, and aptamers utilized in these biosensors typically bind to the extracellular region, with overlapping binding sites that severely constrain the fabrication of biosensors. In this study, we present a simple approach to specifically identify and analyze ExoPD-L1 through the non-selective trapping effect of Ti3C2TX (X=-O, -F, -OH) MXene on exosomes via the formation of Ti-O-P complexation, and the selective capture of peptide-functionalized Au@MPBA (4-Mercaptophenylboronic acid) @SiO2 surface enhanced Raman scattering (SERS) tags on ExoPD-L1. The biosensor delivered a both hypersensitive and reliable performance in exosome detection with a low limit of detection (20.74 particles/mL) in the linear range of 102 to 5×106 particles/mL. Furthermore, the biosensor demonstrated excellent stability and interference resistance in detecting ExoPD-L1 in clinical serum samples, enabling the easy differentiation of breast cancer patients from healthy controls. This work provides new insights into the design of biosensors for exosome detection and can serve as a replicable template for sandwich immunoassay detection for other types of sensors, including but not limited to SERS.

Fabrication of flexible SERS substrate based on Au nanostars and PDMS for sensitive detection of Thiram residue in apple juice

We developed a novel fabrication of flexible surface-enhanced Raman scattering (SERS) substrate to perform selective and sensitive determination of thiram residue in fruits and juices. Au nanostars (Au NSs) with multi-branching structure were self-assembled on aminated Polydimethylsiloxane (PDMS) slides by electrostatic interaction. By measuring the Thiram's characteristic peak intensity at 1371 cm^-1, the SERS method could distinguish Thiram from other pesticide residues. A good linear relationship between the peak intensity at 1371 cm^-1 and thiram's concentration was established at the range from 0.01 ppm to 100 ppm and the Limit of detection is 0.0048 ppm. We directly used this SERS substrate to detect Thiram in apple juice. By standard addition method, recoveries varied in the range of 97.05% to 106.00% and the RSD were from 3.26% to 9.35%. The SERS substrate exhibited a good sensitivity, stability and selectively for the detection of Thiram in food samples, which can be spread as a common method for the detection of pesticides in food samples.

Plasmon-enhanced fluorescence for ellagic acid detection based on surface structure of gold nanoparticles

Ellagic acid (EA), as a natural polyphenolic acid, is considered a naturally occurring inhibitor of carcinogenesis. Herein, we developed a plasmon-enhanced fluorescence (PEF) probe for EA detection based on silica-coated gold nanoparticles (Au NPs). A silica shell was designed to control the distance between silica quantum dots (Si QDs) and Au NPs. The experimental results indicated that an 8.8-fold fluorescence enhancement was obtained compared with the original Si QDs. Three-dimensional finite-difference time-domain (3D-FDTD) simulations further demonstrated that the local electric field enhancement around Au NPs led to the fluorescence enhancement. In addition, the fluorescent sensor was applied for the sensitive detection of EA with a detection limit of 0.14 μM. It can be used to detect EA in pomegranate rind with a recovery rate of 100.26-107.93%. It can also be applied to the analysis of other substances by changing the identification substances. These experimental results indicated that the probe provides a good option for clinical analysis and food safety.

Reusable SERS Substrates Based on Gold Nanoparticles for Peptide Detection

Raman spectroscopy is a powerful analytical technique widely used for quantitative and qualitative analysis. However, the development of inexpensive, reproducible, and reusable enhancing substrates remains a challenge for material scientists and analytical chemists. In this study, we address this challenge by demonstrating the deposition of core-shell nanoparticles consisting of a gold core and a thin inert SiO₂ shell within a confined space, resulting in the formation of a highly efficient Raman-enhancing structure. Nanoparticles were characterized by UV-vis spectroscopy, dynamic light scattering, and total reflectance X-ray fluorescence spectroscopy, whereas the prepared substrates were characterized by scanning electron microscopy and Raman spectroscopy with a model molecule, malachite green. The relationship between Raman intensity and the loading of malachite green dye exhibited linearity, indicating the uniform spatial distribution of hotspots across the substrate. The limit of detection was determined as 2.9 μM of malachite green when 10 uL was distributed over a ca. 25 mm² surface area. Moreover, the same substrate, after thorough washing in ethanol, was successfully employed for the detection of bovine serum albumin at a concentration level of 55 μg mL^-1, demonstrating its reusability and versatility. Our findings highlight the potential of these substrates for various applications in biomedical research, clinical diagnosis, and beyond.

A review on current progress of Raman-based techniques in food safety: From normal Raman spectroscopy to SESORS

Frequently occurrence of food safety incidents has induced global concern over food safety. To ensure food quality and safety, an increasing number of rapid and sensitive analytical methods have been developed for analysis of all kinds of food composition and contaminants. As one of the high-profile analytical techniques, Raman spectroscopy has been widely applied in food analysis with simple, rapid, sensitive, and nondestructive detection performance. Research on Raman techniques is a direction of great interest to many fields, especially in food safety. Hence, it is crucial to gain insight into recent advances on the use of Raman-based techniques in food safety applications. In this review, we introduce Raman techniques from normal Raman spectroscopy to developed ones (e.g., surface enhanced Raman scattering (SERS), spatially offset Raman spectroscopy (SORS), surface-enhanced spatially offset Raman spectroscopy (SESORS)), in view of their history and development, principles, design, and applications. In addition, future challenges and trends of these techniques are discussed regarding to food safety.

Evaluating nanoparticle localisation in glioblastoma multicellular tumour spheroids by surface enhanced Raman scattering

Glioblastoma multiforme (GBM) is a particularly aggressive and high-grade brain cancer, with poor prognosis and life expectancy, in urgent need of novel therapies. These severe outcomes are compounded by the difficulty in distinguishing between cancerous and non-cancerous tissues using conventional imaging techniques. Metallic nanoparticles (NPs) are advantageous due to their diverse optical and physical properties, such as their targeting and imaging potential. In this work, the uptake, distribution, and location of silica coated gold nanoparticles (AuNP-SHINs) within multicellular tumour spheroids (MTS) derived from U87-MG glioblastoma cells was investigated by surface enhanced Raman scattering (SERS) optical mapping. MTS are three-dimensional in vitro tumour mimics that represent a tumour in vivo much more closely than that of a two-dimensional cell culture. By using AuNP-SHIN nanotags, it is possible to readily functionalise the inner gold surface with a Raman reporter, and the outer silica surface with an antibody for tumour specific targeting. The nanotags were designed to target the biomarker tenascin-C overexpressed in U87-MG glioblastoma cells. Immunochemistry indicated that tenascin-C was upregulated within the core of the MTS, however limitations such as NP size, quiescence, and hypoxia, restricted the penetration of the nanotags to the core and they remained in the outer proliferating cells of the spheroids. Previous examples of MTS studies using SERS demonstrated the incubation of NPs on a 2D monolayer of cells, with the subsequent formation of the MTS from these pre-incubated cells. Here, we focus on the localisation of the NPs after incubation into pre-formed MTS to establish a better understanding of targeting and NP uptake. Therefore, this work highlights the importance for the investigation and translation of NP uptake into these 3D in vitro models.

Material design, development, and trend for surface-enhanced Raman scattering substrates

Surface-enhanced Raman scattering (SERS) is a powerful and non-invasive spectroscopic technique that can provide rich and specific chemical fingerprint information for various target molecules through effective SERS substrates. In view of the strong dependence of the SERS signals on the properties of the SERS substrates, design, exploration, and construction of novel SERS-active nanomaterials with low cost and excellent performance as the SERS substrates have always been the foundation and the top priority for the development and application of the SERS technology. This review specifically focuses on the extensive progress made in the SERS-active nanomaterials and their enhancement mechanism since the first discovery of SERS on the nanostructured plasmonic metal substrates. The design principles, unique functions, and influencing factors on the SERS signals of different types of SERS-active nanomaterials are highlighted, and insight into their future challenge and development trends is also suggested. It is highly expected that this review could benefit a complete understanding of the research status of the SERS-active nanomaterials and arouse the research enthusiasm for them, leading to further development and wider application of the SERS technology.

Local cation-tuned reversible single-molecule switch in electric double layer

The nature of molecule-electrode interface is critical for the integration of atomically precise molecules as functional components into circuits. Herein, we demonstrate that the electric field localized metal cations in outer Helmholtz plane can modulate interfacial Au-carboxyl contacts, realizing a reversible single-molecule switch. STM break junction and I-V measurements show the electrochemical gating of aliphatic and aromatic carboxylic acids have a conductance ON/OFF behavior in electrolyte solution containing metal cations (i.e., Na⁺, K⁺, Mg²⁺ and Ca²⁺), compared to almost no change in conductance without metal cations. In situ Raman spectra reveal strong molecular carboxyl-metal cation coordination at the negatively charged electrode surface, hindering the formation of molecular junctions for electron tunnelling. This work validates the critical role of localized cations in the electric double layer to regulate electron transport at the single-molecule level.

A Novel SPR Immunosensor Based on Dual Signal Amplification Strategy for Detection of SARS-CoV-2 Nucleocapsid Protein

Since the global outbreak of coronavirus disease 2019 (COVID-19), it has spread rapidly around the world. The nucleocapsid (N) protein is one of the most abundant SARS-CoV-2 proteins. Therefore, a sensitive and effective detection method for SARS-CoV-2 N protein is the focus of research. Here, we developed a surface plasmon resonance (SPR) biosensor based on the dual signal-amplification strategy of Au@Ag@Au nanoparticles (NPs) and graphene oxide (GO). Additionally, a sandwich immunoassay was utilized to sensitively and efficiently detect SARS-CoV-2 N protein. On the one hand, Au@Ag@Au NPs have a high refractive index and the capability to electromagnetically couple with the plasma waves propagating on the surface of gold film, which are harnessed for amplifying the SPR response signal. On the other hand, GO, which has the large specific surface area and the abundant oxygen-containing functional groups, could provide unique light absorption bands that can enhance plasmonic coupling to further amplify the SPR response signal. The proposed biosensor could efficiently detect SARS-CoV-2 N protein for 15 min and the detection limit for SARS-CoV-2 N protein was 0.083 ng/mL, with a linear range of 0.1 ng/mL~1000 ng/mL. This novel method can meet the analytical requirements of artificial saliva simulated samples, and the developed biosensor had a good anti-interference capability.

Hybrid gold-silica nanoparticles for plasmonic applications: A comparison study of synthesis methods for increasing gold coverage

The current work focuses on the synthesis of hybrid nanoparticles (NPs) made of a silica core (Si NPs) coated with discrete gold nanoparticles (Au NPs), which exhibit localized surface plasmon resonance (LSPR) properties. This plasmonic effect is directly related to the nanoparticles size and arrangement. In this paper, we explore a wide range of size for the silica cores (80, 150, 400, and 600 nm) and for the gold NPs (8, 10, and 30 nm). Some rational comparison between different functionalization techniques and different synthesis methods for the Au NPs are proposed, related to the optical properties and colloidal stability in time. An optimized, robust and reliable synthesis route is established, which improves the gold density and homogeneity. The performances of these hybrid nanoparticles are evaluated in order to be used in the shape of a dense layer for pollutant detection in gas or liquids, and find numerous applications as a cheap and new optical device.

In Situ/Operando Methods for Understanding Electrocatalytic Nitrate Reduction Reaction

With the development of industrial and agricultural, a large amount of nitrate is produced, which not only disrupts the natural nitrogen cycle, but also endangers public health. Among the commonly used nitrate treatment techniques, the electrochemical nitrate reduction reaction (eNRR) has attracted extensive attention due to its mild conditions, pollution-free nature, and other advantages. An in-depth understanding of the eNRR mechanism is the prerequisite for designing highly efficient electrocatalysts. However, some traditional characterization tools cannot comprehensively and deeply study the reaction process. It is necessary to develop in situ and operando techniques to reveal the reaction mechanism at the time-resolved and atomic level. This review discusses the eNRR mechanism and summarizes the possible in situ techniques used in eNRR. A detailed introduction of various in situ techniques and their help in understanding the reaction mechanism is provided. Finally, the current challenges and future opportunities in this research area are discussed and highlighted.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Plasmonic surface-enhanced Raman scattering nano-substrates for detection of anionic environmental contaminants: Current progress and future perspectives

Surface-enhanced Raman scattering spectroscopy (SERS) is a powerful technique of vibrational spectroscopy based on the inelastic scattering of incident photons by molecular species. It has unique properties such as ultra-sensitivity, selectivity, non-destructivity, speed, and fingerprinting properties for analytical and sensing applications. This enables SERS to be widely used in real-world sample analysis and basic plasmonic mechanistic studies. However, the desirable properties of SERS are compromised by the high cost and low reproducibility of the signals. The development of multifunctional, stable and reusable nano-engineered SERS substrates is a viable solution to circumvent these drawbacks. Recently, plasmonic SERS active nano-substrates with various morphologies have attracted the attention of researchers due to promising properties such as the formation of dense hot spots, additional stability, tunable and controlled morphology, and surface functionalization. This comprehensive review focused on the current advances in the field of SERS active nanosubstrates suitable for the detection and quantification of anionic environmental pollutants. The common fabrication methods, including the techniques for morphological adjustments and surface modification, substrate categories, and the design of nanotechnologically fabricated plasmonic SERS substrates for anion detection are systematically presented. Here, the need for the design, synthesis, and functionalization of SERS nano-substrates for anions of great environmental importance is explained in detail. In addition, the broad categories of SERS nano-substrates, namely colloid-based SERS substrates and solid-support SERS substrates are discussed. Moreover, a brief discussion of SERS detection of certain anionic pollutants in the environment is presented. Finally, the prospects in the fabrication and commercialization of pilot-scale handheld SERS sensors and the construction of smart nanosubstrates integrated with novel amplifying materials for the detection of anions of environmental and health concern are proposed.

Cu+-Mediated CO Coordination for Promoting C-C Coupling for CO2 and CO Electroreduction

Selective electrochemical upgrading of CO₂ to multicarbon (C₂₊) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu⁺ in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO₂ reduction. We find that, relative to other halogen anions, iodide (I^-) in HCO₃^- electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu⁺, which can be dynamically stabilized by I^- via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO)_n⁺ complexes, leading to an approximately 3.0-fold increase of C₂₊ Faradaic efficiency at -0.9 V_RHE relative to that of I^--free Cu surfaces. Accordingly, a deliberate introduction of CuI into I^--containing HCO₃^- electrolytes for direct CO electroreduction brings about a 4.3-fold higher C₂₊ selectivity. This work provides insights into the role of Cu⁺ in C-C coupling and the enhanced C₂₊ selectivity for CO₂ and CO electrochemical reduction.

In situ Raman monitoring of electroreductive dehalogenation of aryl halides at an Ag/aqueous solution interface

Electroreductive dehalogenation as an efficient and green approach has attracted much attention in pollution remediation. Herein, we have employed a shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique to in situ probe the electroreductive dehalogenation process of aryl halides with thiol groups at Ag/aqueous solution interfaces. It is found that 4-bromothiophenol (BTP) and 4-chlorothiophenol (CTP) can turn into mixed products of 4,4'-biphenyldithiol (BPDT) and thiophenol (TP) as the electrode potential decreases. The conversion ratios estimated from the Raman intensity variations of C-Cl and C-Br vibrations are 44% and 58% for CTP and BTP in neutral solution, respectively. Furthermore, the quantitative analysis of benzene ring vibrations reveals a C-C cross coupling between the benzene free radical intermediate and adjacent TP product, which results in increased selectivity for biphenyl products at negative potentials.

Study of a High-Voltage NMC Interphase in the Presence of a Thiophene Additive Realized by Operando SHINERS

Improving the electrochemical properties and cycle life of high-voltage cathodes in lithium-ion batteries requires a deep understanding of the structural properties and failure mechanisms at the cathode electrolyte interphase (CEI). We present a study implementing an advanced Raman spectroscopy technique to specifically address the compositional features of interphase during cell operation. Our operando technique, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), provides a reliable platform to investigate the dynamics of the interphase structure and elucidate the compositional changes near the cathode surface. To improve the CEI properties, thiophene was introduced and investigated as an effective, high-voltage film-forming additive by largely diminishing the capacity fading triggered at high potentials in LiNi_1/3Co_1/3Mn_1/3O₂ cathodes. While the cells without thiophene show severe capacity fading, cells with an optimized concentration of thiophene exhibit a significant performance improvement. Operando SHINERS detects the presence of a stable CEI. The results suggest that the composition of the CEI is dominated by polythiophene and copolymerization products of ethylene carbonate with thiophene, which protects the electrolyte components from further decomposition. The formation mechanism of the polymeric film was modeled using quantum chemistry calculations, which shows good agreement with the experimental data.

Aptasensor-based assay for dual-readout determination of aflatoxin B1 in corn and wheat via an electrostatic force-mediated FRET strategy

A rapid and sensitive aptasensor was established for the dual-readout determination of aflatoxin B1 (AFB1) utilizing an electrostatically mediated fluorescence resonance energy transfer (FRET) signal amplification strategy. In the presence of AFB1, the aptamer preferentially bound to AFB1, resulting in the aggregation of bare gold nanoparticles (AuNPs) induced by NaCl, accompanied by a change of AuNP solution from wine-red to purple. This color change was used for colorimetric channel analysis. Then, the positively charged quantum dots were introduced into reaction system and interacted with negatively charged AuNPs, which successfully converted the color signal into a more sensitive fluorescence signal through FRET. The fluorescence quenching efficiency decreased with increasing concentrations of AFB1, and the fluorescence of aptasensor gradually recovered. The variation of fluorescence intensity was employed for fluorometric channel analysis. Under the optimal conditions, the color and fluorescence signals exhibited excellent response to AFB1 concentration within the ranges 10-320 ng·mL^-1 and 3-320 ng·mL^-1, respectively, and the limit of detection was as low as 7.32 ng·mL^-1 and 1.48 ng·mL^-1, respectively. The proposed aptasensor exhibited favorable selectivity, good recovery (85.3-113.4% in spiked corn and wheat samples), stable reproducibility (RSD<13.3%), and satisfactory correlation with commercial kits (R²=0.998). The aptasensor developed integrates advantages of modification-free, dual-readout, self-calibration, easy operation, and cost-effectiveness, while providing a simple and universal strategy for rapid and sensitive detection of mycotoxins in foodstuffs.

Magnetic SERS Strip Based on 4-mercaptophenylboronic Acid-Modified Fe3O4@Au for Active Capture and Simultaneous Detection of Respiratory Bacteria

The rapid diagnosis and detection of respiratory bacteria at the early stage can effectively control the epidemic spread and bacterial infection. Here, we designed a rapid, ultrasensitive, and quantitative lateral flow immunoassay (LFA) strip for simultaneous detection of respiratory bacteria S. aureus and S. pneumoniae. In this assay, the surface enhanced Raman scattering (SERS) tags were designed through combining magnetite Raman enhancement nanoparticle Fe₃O₄@Au/DTNB and recognition element 4-mercaptophenylboronic acid (4-MPBA). Further, 4-MPBA could capture multiple bacteria in a complex environmental solution. Based on the strategies, Fe₃O₄@Au/DTNB-mediated magnetic enrichment and 4-MPBA-mediated universal capture capabilities improved the detection sensitivity, the limits of detection for S. aureus and S. pneumoniae were as low as 8 and 13 CFU mL^-1, respectively, which were more sensitive than those of colloidal gold method. The Fe₃O₄@Au/DTNB/Au/4-MPBA-LFA also exhibited good reproducibility, excellent specificity, and high recovery rates in sputum samples, indicating its potential application in the detection of respiratory bacteria samples.

Interaction of Bis-(sodium-sulfopropyl)-Disulfide and Polyethylene Glycol on the Copper Electrodeposited Layer by Time-of-Flight Secondary-Ion Mass Spectrometry

The interactions of the functional additives SPS (bis-(sodium-sulfopropyl)-disulfide) and polyethylene glycol (PEG) in the presence of chloride ions were studied by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) in combination with cyclic voltammetry measurements (CV). The PEG, thiolate, and chloride surface coverages were estimated and discussed in terms of their electrochemical suppressing/accelerating abilities. The conformational influence of both the gauche/trans thiolate molecules, as well as around C-C and C-O of PEG, on the electrochemical properties were discussed. The contribution of the hydrophobic interaction of -CH₂-CH₂- of PEG with chloride ions was only slightly reduced after the addition of SPS, while the contribution of Cu-PEG adducts diminished strongly. SPS and PEG demonstrated significant synergy by significant co-adsorption. It was shown that the suppressing abilities of PEG that rely on forming stable Cu-PEG adducts, identified in the form C₂H₄O₂Cu⁺ and C₃H₆OCu⁺, were significantly reduced after the addition of SPS. The major role of thiolate molecules adsorbed on a copper surface in reducing the suppressing abilities of PEG rely on the efficient capture of Cu²⁺ ions, diminishing the available copper ions for the ethereal oxygen of PEG.

Quantitatively Revealing the Anomalous Enhancement in Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy Using Single-Nanoparticle Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is an ultrasensitive spectroscopic technique that has been extensively applied in the studies of catalysis, electrochemistry, material science, etc.; however, it is substrate and material limited. The development of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) effectively offsets this limitation that attracts enormous attention due to its potential to be applied to any surface. As the core of the SHINERS technique, the inert shell prevents the exposure of the active metal surface, however, also significantly enlarges the metallic gap where the light is trapped. Consequently, the shell is widely considered a side issue to debilitate the coupling efficiency and hinder the sensitivity of SHINERS without systematic studies. Herein, we investigate the shell and structural effect of SHINERS by performing the quantitative optical and structural characterization of single nanostructures. By a statistic of over two hundred nanostructures, we observe that the field enhancement loss due to the shell could be overcome by optimizing the coupling geometry of the shell-isolated nanoparticles (SHINs). An example of SHIN dimers shows even higher field enhancement than their bare Au nanoparticle counterparts as confirmed and explained by FDTD simulations. We demonstrate the signal enhancement of SHINERS saturates with the increasing number of hot spots but could be further optimized by altering the aggregation geometries of the nanoparticles. The sensitivity improvement of the SHINERS technique will boost its broader applications in material science.

Studies of Bis-(Sodium-Sulfopropyl)-Disulfide and 3-Mercapto-1-Propanesulfonate on/into the Copper Electrodeposited Layer by Time-of-Flight Secondary-Ion Mass Spectrometry

Interactions of functional additives SPS (bis-(sodium-sulfopropyl)-disulfide), MPS (3-Mercapto-1-Propanesulfonate), and Cl accumulated and incorporated on/into a copper electrodeposited layer were studied using time-of-flight secondary-ion mass spectrometry (TOF-SIMS) in combination with cyclic voltammetry measurements (CV). It was shown that the Cl and MPS surface coverage is dependent on the applied overpotential and concentration of Cl, SPS, or MPS in the solution. Detailed discussion on the mechanism of yielding CH₂SO₃^-, C₃H₅SO₃^-, CuSC₃H₆SO₃^-, and CuS^- fragments and their assignment to the gauche or trans conformation was proposed. The mechanism of the process of incorporation and re-adsorption of MPS on/into a copper surface under electrochemical conditions without and with chloride ions and its impact on electrochemical properties was proposed. Moreover, it was shown that the presence of chloride ions, the ratio gauche/trans of MPS molecules, as well as the ratio chloride/thiols demonstrate a high impact on the accelerating abilities. Comparative studies conducted under open circuit potential conditions on the nitinol and copper substrate allowed for the identification of specific reactions/interactions of MPS, or SPS and Cl ions on the nitinol and copper surface.

Recent Progress on Solid Substrates for Surface-Enhanced Raman Spectroscopy Analysis

Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique with distinguished features of non-destructivity, ultra-sensitivity, rapidity, and fingerprint characteristics for analysis and sensors. The SERS signals are mainly dependent on the engineering of high-quality substrates. Recently, solid SERS substrates with diverse forms have been attracting increasing attention due to their promising features, including dense hot spot, high stability, controllable morphology, and convenient portability. Here, we comprehensively review the recent advances made in the field of solid SERS substrates, including their common fabrication methods, basic categories, main features, and representative applications, respectively. Firstly, the main categories of solid SERS substrates, mainly including membrane substrate, self-assembled substrate, chip substrate, magnetic solid substrate, and other solid substrate, are introduced in detail, as well as corresponding construction strategies and main features. Secondly, the typical applications of solid SERS substrates in bio-analysis, food safety analysis, environment analysis, and other analyses are briefly reviewed. Finally, the challenges and perspectives of solid SERS substrates, including analytical performance improvement and largescale production level enhancement, are proposed.