In-situ electrochemical surface-enhanced Raman spectroscopy in metal/polyelectrolyte interfaces

Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis.Herein,we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces.The Ag/AgCl and Ag/Ag_(2)O electrodes are used as the reference electrode in the acidic and the alkaline systems,respectively.The working electrode is made of a transparent carbon thin film which loads the electrocatalysts.The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes.The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.

Optical penetration of surface-enhanced micro-scale spatial offset Raman spectroscopy in turbid gel and biological tissue

The limited penetration of photons in biological tissue restricts the deep-tissue detection and imaging application.The micro-scale spatially offset Raman spectroscopy(micro-SORS)with an optical fiber probe,colleting photons from deeper regions by offsetting the position of laser excitation from the collection optics in a range of hundreds of microns,shows great potential to be integrated with endoscopy for inside-body noninvasive detection by circumventing this restric-tion,particularly with the combination of surface-enhanced Raman spectroscopy(SERS).However,a detailed tissue penetration study of micro-SORS in combination with SERS is still lacking.Herein,we compared the signal decay of enhanced Raman nanotags through the tissue phantom of agarose gel and the biological tissue of porcine muscle in the near-infrared(NIR)region using a portable Raman spectrometer with a micro-SORS probe(2.1 mm in diameter)and a conventional hand-held probe(9.7mm in diameter).Two kinds of Raman nanotags were prepared from gold nanorods decorated with the nonresonant(4-nitrobenzenethiol)or resonant Raman reporter molecules(IR-780 iodide).The SERS measurements show that the penetration depths of two Raman nanotags are both over 2 cm in agarose gel and 3 mm in porcine muscle.The depth could be improved to over 4 cm in agarose gel and 5 mm in porcine tissue when using the micro-SORS system.This demonstrates the superiority of optical-fiber micro-SORS system over the conventional Raman detection for the detection of nanotags in deeper layers in the turbid medium and biological tissue,offering the possibility of combining the micro-SORS technique with SERS for noninvasive in vivo endoscopy-integrated clinical application.

Surface-enhanced Raman spectroscopy of serum predicts sensitivity to docetaxel-based chemotherapy in patients with metastatic castration-resistant prostate cancer

Docetaxel-based chemotherapy,as the first-line treatment for metastatic castration-resistant prostate cancer(mCRPC),has succeeded in helping quite a number of patients to improve quality of life and prolong survival time.However,almost half of mCRPC patients are not sensitive to docetaxel chemotherapy initially.This study aimed to establish models to predict sensitivity to docetaxel chemotherapy in patients with mCRPC by using serum surface-enhanced Raman spectroscopy(SERS).A total of 32 mCPRC patients who underwent docetaxel chemo-therapy at our center from July 2016 to March 2018 were included in this study.Patients were dichotomized in prostate-specific antigen(PSA)response group(n=17)versus PSA failure group(n=15)according to the response to docetaxel.In total 64 matched spectra from 32 mCRPC patients were obtained by using SERS of serum at baseline(q0)and after 1 cycle of docetaxel chemotherapy(ql).Comparing Raman peaks of serum samples at baseline(q0)be-tween two groups,significant differences revealed at the peaks of 638,810,890(p<0.05)and 1136cm^(-1)(p<0.01).The prediction models of peak 1363 cm^(-1)and principal component anal-ysis and linear discriminant analysis(PCA-LDA)based on Raman data were established,re-spectively.The sensitivity and specificity of the prediction models were 71%,80%and 69%,78%through the way of leave-one-out cross-validation.According to the results of five-cross-valida-tion,the PCA-LDA model revealed an accuracy of 0.73 and AUC of 0.83.

Sensitive and Label-Free Detection of Protein Secondary Structure by Amide Ⅲ Spectral Signals using Surface-Enhanced Raman Spectroscopy

Proteins and peptides perform a vital role in living systems, however it remains a challenge for accurate description of proteins at the molecular level. Despite that surface-enhanced Raman spectroscopy (SERS) can provide the intrinsic fingerprint information of samples with ultrahigh sensitivity, it suffers from the poor reproducibility and reliability. Herein, we demonstrate that the silver nanorod array fabricated by an oblique angle deposition method is a powerful substrate for SERS to probe the protein secondary structures without exogenous labels. With this method, the SERS signals of two typical proteins (lysozyme and cytochrome c) are successfully obtained. Additionally, by analyzing the spectral signals of the amide Ⅲ of protein backbone, the influence of concentration on the folding status of proteins has been elucidated. With the concentration increasing, the components of α-helix and β-sheet structures of lysozyme increase while the secondary structures of cytochrome c almost keep constant. The SERS method in this work offers an effective optical marker to characterize the structures of proteins.

Surface-enhanced resonance Raman scattering spectroscopy of single R6G molecules

Surface-enhanced resonance Raman scattering （SERRS） of Rhodamine 6G （R6G） adsorbed on colloidal silver clusters has been studied. Based on the great enhancement of the Raman signal and the quench of the fluorescence, the SERRS spectra of R6G were recorded for the samples of dye colloidal solution with different concentrations. Spectral inhomogeneity behaviours from single molecules in the dried sample films were observed with complementary evidences, such as spectral polarization, spectral diffusion, intensity fluctuation of vibrational lines and even ＂breathing＂ of the molecules. Sequential spectra observed from a liquid sample with an average of 0.3 dye molecules in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1 or 2 molecules. Difference between the SERRS spectra of R6G excited by linearly and circularly polarized light were experimentally measured.

Identification and analysis of serum samples by surface-enhanced Raman spectroscopy combined with characteristic ratio method and PCA for gastric cancer detection

This study aimed to explore the application of surface-enhanced Raman scattering(SERS)in the rapid diagnosis of gastric cancer.The SERS spectra of 68 serum samples from gastric cancer patients and healthy volunteers were acquired.The characteristic ratio method(CRM)and principal component analysis(PCA)were used to differentiate gastric cancer serum from normal serum.Compared with healthy volunteers,the serum SERS intensity of gastric cancer patients was relatively high at 722 cm^(-1),while it was relatively low at 588,644,861,1008,1235,1397,1445 and 1586 cm^(-1).These results indicated that the relative content of nucleic acids in the serum of gastric cancer patients rises while the relative content of amino acids and carbohydrates decreases.In PCA,the sensitivity and specificity of discriminating gastric cancer were 94.1%and 94.1%,respectively,with the accuracy of 94.1%.Based on the intensity ratios of four characteristic peaks at 722,861,1008 and 1397 cm^(-1),CRM presented the diagnostic sensitivity and specificity of 100%and 97.4%,respectively,and the accuracy of 98.5%.Therefore,the three peak intensity ratios of I_(722)/I_(861),I_(722)/I_(1008)and I_(722)/I_(1397)can be considered as biologicalfingerprint information for gastric cancer diagnosis and can rapidly and directly reflect the physiological and pathological changes associated with gastric cancer development.This study provides an important basis and standards for the early diagnosis of gastric cancer.

A new semi-quantitative Surface-Enhanced Raman Spectroscopy (SERS) method for detection of maleimide (2,5-pyrroledione) with potential application to astrobiology

Nitrogen-containing heterocyclic compounds are fundamental biochemical components of all life on Earth and,presumably,life elsewhere in our solar system.Detection and characterization of these compounds by traditional solvent extraction,chromatographic separation,and GC-MS analysis require more sample mass than will be available from samples returned to Earth from Mars.With its small sample mass requirement,Surface Enhanced Raman Spectroscopy could be an appropriate technique for analysis of returned samples.We have developed a SERS method for the detection of maleimide(2,5-pyrroledione),an N-containing heterocycle with a structure that is widespread in biochemicals.This semi-quantitative methodology accurately determines maleimide concentration in the range from 60 mg/mL to 120 mg/mL.We present a maleimide SERS standard spectrum which will be useful as a reference for future works.The present work demonstrates an easy,accurate,and effective method for the non-destructive qualitative and semi-quantitative study of maleimide as a first step toward developing a method for analysis of related compounds.

Rapid Identification of Legionella Pathogenicity by Surface-Enhanced Raman Spectroscopy

Objective To establish Surface-enhanced Raman Spectroscopy（SERS） can be used as a rapid and reliable method to distinguish virulent strain and mild strain of L. pneumophila. Methods We isolated and characterized of bacterial strains from ATCC and water samples strains, while we analyzed data from SERS technology using gold nanoparticles as a base and cell infections were employed to rapidly detect L. pneumophila strains. Origin 8.0 was used to collect Raman spectra, smooth and homogenize data, and to contrast spectra. Principal component analysis（PCA） was conducted to discriminate differences between groups using the multivariate analysis package Py Chem 3.0.5. Results Our results indicated that the peaks of high virulence strains reached ≥4000. This criterion was verified by subsequent cell experiments. In addition, we also conducted SERS rapid identification on the virulence of several collected clinical strains and obtained accurate results. Conclusion The present study indicates that the established SERS protocol can be used as a rapid and reliable method to distinguish virulent and mildly virulent strains of L. pneumophila, which can be further used in clinical samples.

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy

As an ultrasensitive sensing technology,the application of surface enhanced Raman spectroscopy(SERS)is one interesting topic of nano-optics,which has huge application prospectives in plenty of research fields.In recent years,the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement.In this work,a two-dimensional(2D)Ag nanorice film is fabricated by self-assembly method as a SERS substrate.The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate.The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence.The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices.And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths,which could be a good near IR SERS substrate for bioanalysis.Our work not only enlarges the surface plasmon properties of metal nanostructure,but also exhibits the good application prospect in SERS related fields.

Highly Effective Detection of Amitraz in Honey by Using Surface-Enhanced Raman Scattering Spectroscopy Coupled with Chemometric Methods

As an effective and universal acaricide, amitraz is widely used on beehives against varroasis caused by the mite Varroa jacobsoni. Its residues in honey pose a great danger to human health. In this study, a sensitive, rapid, and environmentally friendly surface-enhanced Raman spectroscopy method (SERS) was developed for the determination of trace amount of amitraz in honey with the use of silver nanorod (AgNR) array substrate. The AgNR array substrate fabricated by an oblique angle deposition technique exhibited an excellent SERS activity with an enhancement factor of -10^7. Density function theory was employed to assign the characteristic peak of amitraz. The detection of amitraz was further explored and amitraz in honey at concentrations as low as 0.08 mg/kg can be identified. Specifically, partial least square regression analysis was employed to correlate the SERS spectra in full-wavelength with Camitraz to afford a multiple-quantitative amitraz predicting model. Preliminary results show that the predicted concentrations of amitraz in honey samples are in good agreement with their real concentrations. Compared with the conventional univariate quantitative model based on single peak’s intensity, the proposed multiple-quantitative predicting model integrates all the characteristic peaks of amitraz, thus offering an improved detecting accuracy and anti-interference ability.

Direct identification of the carbonate intermediate during water-gas shift reaction at Pt-NiO interfaces using surface-enhanced Raman spectroscopy

Noble metal-reducible oxide interfaces have been regarded as one of the most active sites for water-gas shift reaction.However,the molecular reaction mechanism of water-gas shift reaction at these interfaces still remains unclear.Herein,water-gas shift reaction at Pt-NiO interfaces has been in-situ explored using surface-enhanced Raman spectroscopy by construction of Au@Pt@NiO nanostructures.Direct Raman spectroscopic evidence demonstrates that water-gas shift reaction at Pt-NiO interfaces proceeds via an associative mechanism with the carbonate species as a key intermediate.The carbonate species is generated through the reaction of adsorbed CO with gaseous water,and its decomposition is a slow step in water-gas shift reaction.Moreover,the Pt-NiO interfaces would promote the formation of this carbonate intermediate,thus leading to a higher activity compared with pure Pt.This spectral information deepens the fundamental understanding of the reaction mechanism of water-gas shift reaction,which would promote the design of more efficient catalysts.

Surface-enhanced Raman spectroscopy chips based on two-dimensional materials beyond graphene

Surface-enhanced Raman spectroscopy(SERS) based on two-dimensional(2 D) materials has attracted great attention over the past decade. Compared with metallic materials, which enhance Raman signals via the surface plasmon effect, 2 D materials integrated on silicon substrates are ideal for use in the fabrication of plasmon-free SERS chips, with the advantages of outstanding fluorescence quenching capability, excellent biomolecular compatibility, tunable Fermi levels, and potentially lowcost material preparation. Moreover, recent studies have shown that the limits of detection of 2 D-material-based SERS may be comparable with those of metallic substrates, which has aroused significant research interest. In this review, we comprehensively summarize the advances in SERS chips based on 2 D materials. As several excellent reviews of graphene-enhanced Raman spectroscopy have been published in the past decade, here, we focus only on 2 D materials beyond graphene, i.e., transition metal dichalcogenides, black phosphorus, hexagonal boron nitride, 2 D titanium carbide or nitride, and their heterostructures. We hope that this paper can serve as a useful reference for researchers specializing in 2 D materials, spectroscopy, and diverse applications related to chemical and biological sensing.

Multivariate analysis of serum surface-enhanced Raman spectroscopy of liver cancer patients

Early diagnosis of liver cancer plays a significant role in reducing its high mortality.In this preliminary study,the feasibility of using serum surface-enhanced Raman spectroscopy(SERS)to identify liver cancer was studied.Serum samples were obtained from liver cancer patients and healthy controls.The differences between the SERS spectra of pre-operation and postoperation of liver cancer patients were also analyzed.The general shape and trend of SERS spectra of health control and liver cancer patients were similar.Multivariate analysis,e.g.,PLSSVM,might be useful for the discrimination of serum SERS spectra of pre-operation and post-operation.

Diagnosis of knee osteoarthritis by OCT and surface-enhanced Raman spectroscopy

In this paper,optical coherence tomography(OCT)and surface-enhanced Raman spectroscopy(SERS)were used to characterize normal knee joint(NKJ)tissue and knee osteoarthritis(KOA)tissue ex vivo.OCT images show that there is a clear hierarchical structure in NKJ tissue,including surface layer,transitional layer,radiation layer and cartilage matrix calcification layer tissue structure,while the hierarchical structure of KOA tissue is not clear and unevenly distributed,and the pathological tissues at different stages also show significant di®erences.SERS shows that NKJ tissue and mild osteoarthritic knee cartilage(MiKOA)tissue have strong characteristic Raman peaks at 964,1073(1086),1271,1305,1442,1660 and 1763 cm^(-1).Compared with the Raman spectrum of NKJ tissue,the Raman characteristic peaks of MiKOA tissue have some shifts,moving from 1073 cm^(-1)to 1086 cm^(-1)and from 1542 cm^(-1)to 1442 cm^(-1).There is a characteristic Raman peak of 1271 cm^(-1)in MiKOA tissue,but not in NKJ tissue.Compared with NKJ tissue,severely degenerated cartilage(SdKOA)tissues show some new SERS peaks at 1008,1245,1285,1311 and 1321 cm^(-1),which are not seen in SERS spectra of NKJ tissue.Principal component analysis(PCA)was used to analyze the Raman spectra of 1245–1345 cm^(-1)region.The results show that PCA can distinguish NKJ,MiKOA and SdKOA tissues and the accuracy is about 90%.These results indicate that OCT can clearly distinguish NKJ,MiKOA,moderate osteoarthritic knee cartilage(MoKOA)and SdKOA tissue,while SERS can provide further judgment basis.The results also prove that the contents of protein and polysaccharide in knee tissue are changed during the pathological process of knee tissue,which is the cause of pain caused by poor friction in knee joint during movement.

Advancing Energy Systems with In-Situ and Operando Surface-Enhanced Raman Scattering Spectroscopy

Surface-enhanced Raman scattering spectroscopy(SERS)has emerged as a powerful analytical technique to enable nanoscale investigations of energy systems.This mini-review focuses on the applications of in-situ and operando SERS in energy-related research,highlighting its unique capabilities and significant contributions to understanding energy storage and conversion processes.We first introduce the fundamental principles of SERS,key SERS-derived techniques,and commonly employed platforms.Subsequently,we delve into the diverse applications of in-situ and operando SERS across various energy systems,encompassing photocatalytic and electrocatalytic systems,fuel cells,solar cells,and batteries.Finally,we conclude with our perspective on the current challenges and prospects in this area.We hope thismini-review serves as an essential overview to guide the design and implementation of in-situ and operando SERS studies of energy systems.

A core-satellite self-assembled SERS aptasensor containing a“biological-silent region”Raman tag for the accurate and ultrasensitive detection of histamine

Herein,a novel interference-free surface-enhanced Raman spectroscopy(SERS)strategy based on magnetic nanoparticles(MNPs)and aptamer-driven assemblies was proposed for the ultrasensitive detection of histamine.A core-satellite SERS aptasensor was constructed by combining aptamer-decorated Fe_(3)O_(4)@Au MNPs(as the recognize probe for histamine)and complementary DNA-modified silver nanoparticles carrying 4-mercaptobenzonitrile(4-MBN)(Ag@4-MBN@Ag-c-DNA)as the SERS signal probe for the indirect detection of histamine.Under an applied magnetic field in the absence of histamine,the assembly gave an intense Raman signal at“Raman biological-silent”region due to 4-MBN.In the presence of histamine,the Ag@4-MBN@Ag-c-DNA SERS-tag was released from the Fe_(3)O_(4)@Au MNPs,thus decreasing the SERS signal.Under optimal conditions,an ultra-low limit of detection of 0.65×10^(-3)ng/mL and a linear range 10^(-2)-10^5 ng/mL on the SERS aptasensor were obtained.The histamine content in four food samples were analyzed using the SERS aptasensor,with the results consistent with those determined by high performance liquid chromatography.The present work highlights the merits of indirect strategies for the ultrasensitive and highly selective SERS detection of small biological molecules in complex matrices.

Integration of a fused silica capillary and in-situ Raman spectroscopy for investigating CO_(2) solubility in n-dodecane at near-critical and supercritical conditions of CO_(2)

To determine the solubility of CO_(2)in n-dodecane at T=303.15-353.15 K,P≤11.00 MPa,an integrated fused silica capillary and in-situ Raman spectroscopy system was built.The Raman peak intensity ratio(I_(CO_(2))/IC-H)between the upper band of CO_(2)Fermi diad(I_(CO_(2)))and the C-H stretching band of n-dodecane(IC-H)was employed to determine the solubility of CO_(2)in n-dodecane based on the calibrated correlation equation between the known CO_(2)molality in n-dodecane and the I_(CO_(2))/IC-Hratio with R^(2)=0.9998.The results indicated that the solubility of CO_(2)decreased with increasing temperature and increased with increasing pressure.The maximum CO_(2)molality(30.7314 mol/kg)was obtained at 303.15 K and7.00 MPa.Finally,a solubility prediction model(lnS=(P-A)/B)based on the relationship with temperature(T in K)and pressure(P in MPa)was developed,where S is CO_(2)molality,A=-8×10^(-6)T^(2)+0.0354T-8.1605,and B=0.0405T-10.756.The results indicated that the solubilities of CO_(2)derived from this model were in good agreement with the experimental data.

Surface-enhanced vibrational spectroscopies in electrocatalysis:Fundamentals,challenges,and perspectives

Electrocatalysis offers a promising approach towards chemical synthesis driven by renewable energy.Molecular level understanding of the electrochemical interface remains challenging due to its compositional and structural complexity.In situ interfacial specific characterization techniques could help uncover structure-function relationships and reaction mechanism.To this end,electrochemical surface-enhanced Raman spectroscopy(SERS)and surface-enhanced infrared absorption spectroscopy(SEIRAS)thrive as powerful techniques to provide fingerprint information of interfacial species at reaction conditions.In this review,we first introduce the fundamentals of SERS and SEIRAS,followed by discussion regarding the technical challenges and potential solutions.Finally,we highlight future directions for further development of surface-enhanced spectroscopic techniques for electrocatalytic studies.

In-situ Raman observation on crack tips of Vickers indent in PLZT ceramics

Vickers indentation was introduced into the originally in-plane and out-of-plane poled PLZT ceramics.The Raman spectra were in-situ recorded at selected crack tips before and after the indentations,as well as after the applications of external electric field.The results show that the changes in Raman intensities of optical modes could be sensitively related to 90° domain switching around the crack tips which are strongly dependent on the directions of original polarization and geometric locations.When the direction of electric field was perpendicular to the direction of original polarization,the 90° domain switching at crack tips of the Vickers indentation on the originally in-plane poled PLZT ceramics caused most significant change in the Raman intensity,which inhibited the crack growth.However,when the direction of electric field was parallel to the direction of original polarization,the growth of crack tips became predominantly without the 90° domain switching,which led to the crack growth.

Azimuthal vector beam illuminating plasmonic tips circular cluster for surface-enhanced Raman spectroscopy

Noble metallic nanostructures with strong electric near-field enhancement can significantly improve nanoscale light-matter interactions and are critical for high-sensitivity surface-enhanced Raman spectroscopy[SERS].Here,we use an azimuthal vector beam[AVB]to illuminate the plasmonic tips circular cluster[PTCC]array to enhance the electric near-field intensity of the PTCC array,and then use it to improve SERS sensitivity.The PTCC array was prepared based on the self-assembled and inductive coupled plasmon[ICP]etching methods.The calculation results show that,compared with the linearly polarized beam[LPB]and radial vector beam excitations,the AVB excitation can obtain stronger electric near-field enhancement due to the strong resonant responses formed in the nanogap between adjacent plasmonic tips.Subsequently,our experimental results proved that AVB excitation increased SERS sensitivity to 10-13mol/L,which is two orders of magnitude higher than that of LPB excitation.Meanwhile,the PTCC array had excellent uniformity with the Raman enhancement factor calculated to be~2.4×10^[8].This kind of vector light field enhancing Raman spectroscopy may be applied in the field of sensing technologies,such as the trace amount detection.