Shell-isolated Nanoparticle-enhanced Raman Spectroscopy Research Articles

Fe3O4-protected gold nanoparticles: New plasmonic-magnetic nanomaterial for Raman analysis of surfaces

The first example of the application of core–shell nanoparticles with a plasmonic core and a magnetic shell for the shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) analysis of surfaces has been reported. Synthesized Au@Fe3O4 nanoparticles are efficient electromagnetic nanoresonators that induce a significant increase in the efficiency of Raman scattering for molecules in their close proximity. The formed shell layer of Fe3O4 is thin enough not to significantly dampen the electromagnetic enhancement generated by the plasmonic gold core, yet the amount of Fe3O4 is sufficient to allow the nanomaterial to be manipulated by a magnetic field. It is possible to form homogeneous layers of Au@Fe3O4 nanoresonators with different and controllable surface densities using a simple procedure: the deposition of a drop of a sol of Au@Fe3O4 nanoparticles and evaporation of the solvent while the sample is placed in a strong magnetic field. This method of homogeneous deposition of a layer of SHINERS nanoresonators could not be applied for the previously used SHINERS materials due to the so-called coffee ring effect. The possibility of an easily controllable homogeneous deposition of Au@Fe3O4 nanoparticles on the surface of a sample placed on a strong permanent magnet makes these nanoparticles a very promising material for SHINERS.

Plasmonic Core–Shell Nanomaterials and their Applications in Spectroscopies

AbstractPlasmonic core–shell nanostructures have attracted considerable attention in the scientific community recently due to their highly tunable optical properties. Plasmon‐enhanced spectroscopies are one of the main applications of plasmonic nanomaterials. When excited by an incident laser of suitable wavelength, strong and highly localized electromagnetic (EM) fields are generated around plasmonic nanomaterials, which can significantly boost excitation and/or radiation processes that amplify Raman, fluorescence, or nonlinear signals and improve spectroscopic sensitivity. Herein, recent developments in plasmon‐enhanced spectroscopies utilizing core–shell nanostructures are reviewed, including shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS), plasmon‐enhanced fluorescence spectroscopy, and plasmon‐enhanced nonlinear spectroscopy.

Probing Single‐Atom Catalysts and Catalytic Reaction Processes by Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy

AbstractDeveloping 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.

Probing Single-Atom Catalysts and Catalytic Reaction Processes by Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy.

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.

Applications of Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

The surface-enhanced Raman scattering (SERS) is mainly used as an analysis or detection tool of biological and chemical molecules. Since the last decade, an alternative branch of the SERS effect has been explored, and named shell-isolated nanoparticle Raman spectroscopy (SHINERS) which was discovered in 2010. In SHINERS, plasmonic cores are used for enhancing the Raman signal of molecules, and a very thin shell of silica is generally employed for improving the thermal and chemical stability of plasmonic cores that is of great interest in the specific case of catalytic reactions under difficult conditions. Moreover, thanks to its great surface sensitivity, SHINERS can enable the investigation at liquid–solid interfaces. In last two years (2019–2020), recent insights in this alternative SERS field were reported. Thus, this mini-review is centered on the applications of shell-isolated nanoparticle Raman spectroscopy to the reactions with CO molecules, other surface catalytic reactions, and the detection of molecules and ions.

In Situ Surface-Enhanced Raman Spectroscopy Characterization of Electrocatalysis with Different Nanostructures.

As energy demands increase, electrocatalysis serves as a vital tool in energy conversion. Elucidating electrocatalytic mechanisms using in situ spectroscopic characterization techniques can provide experimental guidance for preparing high-efficiency electrocatalysts. Surface-enhanced Raman spectroscopy (SERS) can provide rich spectral information for ultratrace surface species and is extremely well suited to studying their activity. To improve the material and morphological universalities, researchers have employed different kinds of nanostructures that have played important roles in the development of SERS technologies. Different strategies, such as so-called borrowing enhancement from shell-isolated modes and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)-satellite structures, have been proposed to obtain highly effective Raman enhancement, and these methods make it possible to apply SERS to various electrocatalytic systems. Here, we discuss the development of SERS technology, focusing on its applications in different electrocatalytic reactions (such as oxygen reduction reactions) and at different nanostructure surfaces, and give a brief outlook on its development.

A universal polymer shell-isolated nanoparticle (SHIN) design for single particle spectro-electrochemical SERS sensing using different core shapes.

Shell-isolated nanoparticles (SHINs) have attracted increasing interest for non-interfering plasmonic enhanced sensing in fields such as materials science, biosensing, and in various electrochemical systems. The metallic core of these nanoparticles is isolated from the surrounding environment preventing direct contact or chemical interaction with the metal surface, while still being close enough to enable localized surface plasmon enhancement of the Raman scattering signal from the analyte. This concept forms the basis of the shell isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique. To date, the vast majority of SHIN designs have focused on SiO2 shells around spherical nanoparticle cores and there has been very limited published research considering alternatives. In this article, we introduce a new polymer-based approach which provides excellent control over the layer thickness and can be applied to plasmonic metal nanoparticles of various shapes and sizes without compromising the overall nanoparticle morphology. The SHIN layers are shown to exhibit excellent passivation properties and robustness in the case of gold nanosphere (AuNP) and anisotropic gold nanostar (AuNS) core shapes. In addition, in situ SHINERS spectro-electrochemistry measurements performed on both SHIN and bare Au nanoparticles demonstrate the utility of the SHIN coatings. Correlated confocal Raman and SEM mapping was achieved to clearly establish single nanoparticle SERS sensitivity. Finally, confocal in situ SERS mapping enabled visualisation of the redox related molecular structure changes occurring on an electrode surface in the vicinity of individual SHIN-coated nanoparticles.

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

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

Characterization of Electrodeposited Cu Interfaces Via Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy

The advent of SERS created a new avenue for investigating interfacial phenomena by coupling the localized surface plasmon resonance (LSPR) of metal nanostructures to the inelastic scattering properties of molecules. Seeing a 104-fold enhancement in Raman signals, SERS scattering events were used to identify adsorbed molecules and substrate-surface structural conformations. But, even with the advent of SERs, Raman spectroscopy was still confined to LSPR active materials with roughened surfaces. However, recent technical modifications to SERS, such as shell-isolation and localized probe modes, have shown potential for the operando investigation of flat non-plasmon active single-crystal surfaces. Shell-isolated Nanoparticle Enhanced Raman Spectroscopy(SHINERS) provides two parallel paths for electric field enhancement of non-plasmon active surfaces while minimizing chemical perturbations by encasing reporters in a chemically inert shell (Figure 1). This technique can be used to perform measurements before, during, and after electrodeposition to gain an understanding for changes at metal-solution interfaces under an applied bias. SHINERS serves as a great utility to not only understand surface adsorbates, but to also characterize how dynamic surfaces respond to surface adsorbates. The precarious nature of metastable surfaces (e.g. metallic Cu) make capturing surface information challenging, preventing accurate structure-activity assignments necessary to fully understand the system. The lack of techniques (operando, especially) capable of evaluating functional interfaces, vs model systems, has further inhibited understanding of surface phenomena. Breaking these limits, will enable novel findings that afford new understanding and strategies to develop refined interfaces and processes. Herein, we report the synthesis of Au@SiO2 core-shell nanoparticles and their application to track the state of interfacial phenomena on electrodeposited Cu surfaces (Figure 1).Figure 1. Electron microscopy images of Au-SiO2 nanoparticles (a) dispersed on Cu Trenches (b) for shell-isolated nanoparticle enhanced Raman spectroscopy (c) measurements to probe for surface adsorbates, which shows enhancement relative to the bare Cu surface (d). Figure 1

In Situ Raman Study of CO Electrooxidation on Pt(hkl) Single-Crystal Surfaces in Acidic Solution.

The adsorption and electrooxidation of CO molecules at well-defined Pt(hkl) single-crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top- and bridge-site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top-site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre-oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti-poisoning and highly effective catalysts.

In Situ Raman Study of CO Electrooxidation on Pt(hkl) Single‐Crystal Surfaces in Acidic Solution

AbstractThe adsorption and electrooxidation of CO molecules at well‐defined Pt(hkl) single‐crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top‐ and bridge‐site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top‐site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre‐oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti‐poisoning and highly effective catalysts.

Synthesis and comparison of gold nanoparticles coated with silicon, manganese and titanium dioxides

The synthesized gold nanoparticles (50–60 nm) were coated with thin (1.5–8 nm) layers of silicon, manganese and titanium dioxides. The obtained three species of nanospheres were applied for the analysis of self-assembled monolayer of thiophenol by shell-isolated nanoparticleenhanced Raman spectroscopy method. Detailed synthesis and comparison of the particle properties are provided in this report.

Observation of Substituent Effects in the Electrochemical Adsorption and Hydrogenation of Alkynes on Pt{hkl} Using SHINERS.

By combining cyclic voltammetry (CV) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), the adsorption behavior of two alkynes, propargyl alcohol (PA) and 2-methyl-3-butyn-2-ol (MeByOH), undergoing hydrogenation on Pt basal plane single-crystal electrodes is investigated. It is found that PA and MeByOH give rise to strong surface sensitivities in relation to both hydrogenation activity and molecular fragmentation into adsorbed species such as CO. For PA, irreversible adsorption is strongly favored for Pt{100} and Pt{110} but is weak in the case of Pt{111}. It is suggested that the presence of the primary alcohol substituent is key to this behavior, with the order of surface reactivity being Pt{100} > Pt{110} > Pt{111}. In contrast, for MeByOH, strong irreversible adsorption is observed on all three basal plane Pt surfaces and we propose that this reflects the enhanced activity of the alkyne moiety arising from the inductive effect of the two methyl groups, coupled with the decreased activity of the tertiary alcohol substituent toward fragmentation. Pt{111} also exhibits singular behavior in relation to MeByOH hydrogenation in that a sharp Raman band at 1590 cm–1 is observed corresponding to the formation of a di-σ/π-bonded surface complex as the alkyne adsorbs. This band frequency is some 20 cm–1 higher than the analogous broadband observed for PA and MeByOH adsorbed on all other basal plane Pt surfaces and may be viewed as a fingerprint of Pt{111} terraces being present at a catalyst surface undergoing hydrogenation. Insights into the hydrogenation activity of different Pt{hkl} surfaces are obtained using quantitative comparisons between Raman bands at hydrogenation potentials and at 0.4 V vs Pd/H, the beginning of the double-layer potential region, and it is asserted (with support from CV) that Pt{110} is the most active plane for hydrogenation due to the presence of surface defects generated via the lifting of the (1 × 2) to (1 × 1) clean surface reconstruction following flame annealing and hydrogen cooling. Our findings are also consistent with the hypothesis that Pt{111} planes are most likely to provide semihydrogenation selectivity of alkynes to alkenes, as reported previously.

Silica shell-isolated gold nanospheres: Synthesis, investigation of stability in organic solvents, and application in shell-isolated nanoparticle-enhanced Raman spectroscopy

Abstract Shell-isolated nanoparticles spread over the surface of sample material are widely used in various fields of analysis. Their stability has not yet been well established. In this report, the silica shell-isolated gold nanospheres were synthesized in aqueous medium. Their stability in water and 17 organic solvents was observed visually and employing spectroscopic UV and Raman techniques. The nanoparticles onto self-assembled monolayer of thiophenol were used to amplify Raman signal.

Graphene‐coated Au nanoparticle‐enhanced Raman spectroscopy

AbstractSurface‐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.

Electrochemical SHINERS investigation of the adsorption of butyl xanthate and 2-mercaptobenzothiazole on pyrite

In this paper, shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been applied to investigate the adsorption of typical collectors, butyl xanthate and 2-mercaptobenzothiazole (MBT), on pyrite surface. With the help of inert shell isolated gold nanoparticles as electric field enhancers, high quality electrochemical spectra were obtained in relation to real-world flotation conditions, enabling the quantitative identification of the chemical reactions occurring only on the mineral surface. It has been found that polysulphide anions are predominant oxidation product of pyrite after abrading and above 0 mV vs Ag/AgCl. Both the adsorption of xanthate and MBT are suppressed on pre-oxidized pyrite surface. The pre-formed polysulphide is diminished at negative potentials, which are favourable for collector’s adsorption. Compared to xanthate, MBT shows greater resistance to pyrite oxidation and a broader potential window for adsorption due to the presence of two “minerophilic” groups (endocyclic nitrogen atom bonding in addition to the interaction through the exocyclic S atom). Single exocyclic S atom bonding is predominant in more favarouble adsorption environments. Dithiolate, the oxidation products of xanthate and MBT, has been precluded due to the high stability of adsorbed collector. This is inconsistent with the ex-situ XPS measurement where air exposure may induce oxidation.

Molecular fingerprint of precancerous lesions in breast atypical hyperplasia.

ObjectiveTo identify atypical hyperplasia (AH) of the breast by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), and to explore the molecular fingerprinting characteristics of breast AH.MethodsBreast hyperplasia was studied in 11 hospitals across China from January 2015 to December 2016. All patients completed questionnaires on women’s health. The differences between patients with and without breast AH were compared. AH breast lesions were detected by Raman spectroscopy followed by the SHINERS technique.ResultsThere were no significant differences in clinical features and risk-related factors between patients with breast AH (n = 37) and the control group (n = 2576). Fifteen cases of breast AH lesions were detected by Raman spectroscopy. The main different Raman peaks in patients with AH appeared at 880, 1001, 1086, 1156, 1260, and 1610 cm−1, attributed to the different vibrational modes of nucleic acids, β-carotene, and proteins. Shell-isolated nanoparticles had different enhancement effects on the nucleic acid, protein, and lipid components in AH.ConclusionRaman spectroscopy can detect characteristic molecular changes in breast AH lesions, and may thus be useful for the non-invasive early diagnosis and for investigating the mechanism of tumorigenesis in patients with breast AH.

Shell-isolated nanoparticle-enhanced Raman spectroscopy for characterization of living yeast cells.

Studying the biochemistry of yeast cells has enabled scientists to understand many essential cellular processes in human cells. Further development of biotechnological and medical progress requires revealing surface chemistry in living cells by using a non-destructive and molecular structure sensitive technique. In this study shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was applied for probing the molecular structure of Metschnikowia pulcherrima yeast cells. Important function of studied cells is the ability to eliminate iron from growth media by precipitating the insoluble pigment pulcherrimin. Comparative SERS and SHINERS analysis of the yeast cells in combination with bare Au and shell-isolated Au@SiO2 nanoparticles were performed. It was observed that additional bands, such as adenine ring-related vibrational modes appear due to interaction with bare Au nanoparticles; the registered spectra do not coincide with the spectra where Au@SiO2 nanoparticles were used. SHINERS spectra of M. pulcherrima were significantly enhanced comparing to the Raman spectra. Based on first-principles calculations and 830-nm excited Raman analysis of pulcherrimin, the SHINERS signatures of iron pigment in yeast cells were revealed. Being protected from direct interaction of metal with adsorbate, Au@SiO2 nanoparticles yield reproducible and reliable vibrational signatures of yeast cell wall constituents.

In-Operando characterization of Electrochemical Interfaces Via Shiners: Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy

The advent of SERS created a new avenue for investigating interfacial phenomena by coupling the localized surface plasmon resonance (LSPR) of metal nanostructures to the inelastic scattering properties of molecules. Seeing a 104-fold enhancement in Raman signals, SERS scattering events were used to identify adsorbed molecules and substrate-surface structural conformations. But, even with the advent of SERs, Raman spectroscopy was still confined to LSPR active materials with roughened surfaces. However, recent technical modifications to SERS, such as shell-isolation and localized probe modes, have shown potential for the in-operando investigation of flat non-plasmon active single-crystal surfaces. Shell-isolated Nanoparticle Enhanced Raman Spectroscopy(SHINERS) provides two parallel paths for electric field enhancement of non-plasmon active surfaces while minimizing chemical perturbations by encasing reporters in a chemically inert shell (Figure 1). This technique can be used to perform in-operando measurements during electrochemical processes to bridge the gap between observing and understanding the state of metallic interfaces under an applied bias. This serve as a great utility to not only understand surface adsorbates, but to also characterize dynamic surfaces (e.g. Cu) that undergo reconstruction in response to the applied biases. Such metastable surfaces can impede capturing surface structure information, preventing accurate structure-activity assignments necessary to further understanding of the system. Furthermore, a lack of in-operando technology has inhibited the characterization of active sites and surface phenomena via in-situ measurements. These limitations have resulted in uncertainty of how novel findings are interconnected and ways to design refined interfaces. Herein, I report the synthesis of SiO2 encapsulated Au NPs and their application in-operando to track the state of Cu interfaces under varying electrochemical and chemical conditions. Figure 1

Fundamental understanding and applications of plasmon-enhanced Raman spectroscopy

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