Surface Enhanced Raman Spectroscopy Spectroscopy Research Articles

Reliable and easy-to-use SERS spectroscopy probe using a tapered opto-fluidic photonic crystal fiber.

Surface enhanced Raman spectroscopy (SERS) is one of the most sensitive biosensing techniques that offers label free detection for a variety of applications. Generally, SERS spectroscopy is performed on nano-functionalized planar substrates with plasmonic structures or colloidal nanoparticles. Recently, photonic crystal fibers (PCFs) have gained great interest for SERS based bio sensing applications due to the immense advantages such as improved sensitivity, flexibility and remote sensing capability that it offers compared to the planar substrates. However, the use of PCF based biosensors demand the alignment of it under a microscope, which can affect the reliability of SERS measurements and could be restrictive for practical end use applications. Herein, we aim to develop a tapered suspended core PCF fiber (Tapered-SuC-PCF) that represents an improvement in coupling efficiency and measurement reliability as well as it opens the way to the development of an easy-to-use bio-sensing probes with a plug and play option with conventional Raman spectrometers. We have fabricated several samples of the optimized tapered-SuC-PCF and demonstrated its superior SERS performance compared to standard SuC-PCF fibers with 2 µm core diameter. An excellent SERS measurement reliability is demonstrated using such a fiber in a plug and play type system demonstrating its versatility for practical end use applications.

The influence of amine structure on the mechanism of CO2 facilitated transport across amine-functionalized polymer membranes: An operando spectroscopy study

The influence of the amine structure (secondary, tertiary, pyridinic) in amine-functionalized polymeric membranes on the mechanism of CO2 transport across the membrane is investigated in this work using operando surface enhanced Raman spectroscopy (SERS) and in-situ transmission FTIR spectroscopy. Specifically, the mechanism of CO2 transport across poly-N-methyl-N-vinylamine (PMVAm), poly-N, N-dimethyl-N-vinylamine (PDVAm), and poly(4-vinylpyridine) (P4VP) membranes was investigated by measuring CO2 permeances/selectivities of the membranes and simultaneously detecting CO2 transport intermediates (e.g., carbamate, bicarbonate) formed in the membrane under operating conditions using SERS and FTIR spectroscopy. While permeation measurements suggest that CO2 moves across all membranes via a facilitated transport mechanism, operando SERS and in-situ FTIR results suggest that the molecular-level details of the facilitated transport process are highly sensitive to the structure of the amine functional group. For membranes with secondary (PMVAm) and tertiary (PDVAm) amines, CO2 moves across the membrane as a mixture of both carbamate and bicarbonate species. For P4VP, which has pyridinic amine groups, no CO2-derived intermediates were detected suggesting a new facilitated transport mechanism involving weak interactions between CO2 and the pyridinic nitrogen group without transformation of CO2 into carbamate, bicarbonate, or other intermediate species. Such a facilitated transport mechanism has not been reported in the literature to our knowledge.

Comparison of surface enhanced Raman spectroscopy and Raman spectroscopy for the detection of breast cancer based on serum samples

In this study, surface enhanced Raman spectroscopy (SERS) and Raman spectroscopy (RS), are employed for the classification of different stages of breast cancer using clinically diagnosed serum samples from breast cancer patients and healthy individuals. These serum samples are compared for their spectral features acquired by SERS and RS to establish spectral features that can be considered as spectral markers of breast cancer diagnosis and classification. SERS features related to DNA, proteins and lipids were observed which are solely observed in the serum samples of patients at different stages of breast cancer as compared to healthy samples. In order to explore the capability of SERS and RS and their comparison as an analytical tool for the efficient understanding of the progression of breast cancer, Principal Component Analysis (PCA) is done for the SERS and RS spectra of control, stage 2, stage 3 and stage 4. Furthermore, the Partial Least Squares-Discriminant Analysis (PLS-DA) was performed to compare the diagnostic performance of SERS and Raman spectroscopy for the classification of disease positive samples and healthy ones. The sensitivity and specificity and area under receiver operating characteristic (AUROC) curve values for SERS data were 90%, 98.4%, and 94% respectively which were higher as compared to Raman spectral data for which these values were found to be 88.2%, 97.7%, and 83.4% respectively.

The shining brightness of daylight fluorescent pigments: Raman and SERS study of a modern class of painting materials

Raman and surface enhanced Raman spectroscopy (SERS) are established techniques allowing for fast and sensitive identification of dyes and pigments. To date, Raman has only limitedly been applied to the identification of daylight fluorescent pigments, despite this modern class of materials has been adopted by several significant artists (e.g. Frank Stella, Peter Halley, Andy Warhol, and Keith Haring).In this study, seven commercial daylight fluorescent pigments from Radiant were investigated by Raman and SERS spectroscopy. A new type of silver colloid, consisting mainly of rod-like silver nanostructures guaranteeing a high SERS enhancement, has been employed here for the first time in cultural heritage studies.As the number of fluorescent dyes suitable for the manufacturing of daylight fluorescent pigments is limited, these materials are often constituted by a mixture of dyes. Since SERS is not able to physically separate multiple dyes in mixtures, to reveal the complex composition of these materials the coupling of SERS with a separation technique proved to be mandatory. Thin-layer chromatography, being a cost-effective and fast procedure, was chosen for this purpose. The identification of each component was made possible by the comparison of SERS spectra from standard fluorescent dyes, thus increasing the available SERS database for modern materials.Lastly, the analytical protocol was applied to a modern artwork called “Rosso verde nero”, made in 1968 by the Italian artist Carla Accardi, who used to paint on plastic surfaces with fluorescent colours.

Paper-based SERS analysis with smartphones as Raman spectral analyzers.

SERS (Surface Enhanced Raman Spectroscopy) can realize fingerprint recognition of molecular samples with high detection accuracy and sensitivity. However, rapid and convenient measurement of the Raman spectra of analytes for a point-of-care test (POCT) has put forward a high demand for portable Raman spectrometers, as well as reliable SERS substrates. Hereby, we first utilize a smartphone as a miniaturized Raman spectral analyzer, which has the revolutionary advantages of a friendly human-machine interface, fast measurement time, and good sensitivity. Meanwhile, a paper-based SERS chip was prepared based on commonly used filter paper and silver nanoparticles (AgNP), which was successfully used to detect low concentrations of typical SERS analyte model molecules including rhodamine 6G and crystal violet. The current method of smartphone-based SERS spectroscopy as a POCT device will greatly promote the application of Raman technology in a variety of scenarios, such as safety inspections, pesticide residue detection, water pollution monitoring, and so on. Coupled with paper-based SERS chips with advantages of facile preparation, low cost and good reliability, the current work proves to have a great potential for industrial production and for meeting the vast marketing demand of Raman based POCT technology.

Detection and characterization at nM concentration of oligomers formed by hIAPP, Aβ(1-40) and their equimolar mixture using SERS and MD simulations.

We report a structural investigation on IAPP, Aβ(1-40) and their equi-molar mixture aggregation pathway at nano-molar concentration using the Surface Enhanced Raman Spectroscopy (SERS) effect induced by silver metal colloids prepared by laser processes in solution and molecular dynamics simulations. Our data show the ability of silver NPs coupled with SERS to detect secondary structures of IAPP, Aβ(1-40) and their 1 : 1 molar ratio mixture in the oligomeric state. The preparation of silver colloids shows superior performance with respect to chemically prepared nano-particles. SERS spectroscopy shows both selectivity and sensitivity in detecting the secondary structures of hIAPP and Aβ(1-40) and to recognize both proteins in their mixture. On the other hand, molecular dynamics simulations confirm SERS structural data and the given atomistic details about the structural organization of IAPP and Aβ(1-40) oligomers. Our study shows an inhomogeneity in the chemical composition of IAPP/Aβ(1-40) oligomer aggregates.

Application of FTIR and SERS spectroscopy in analysis and discrimination of bacteria and their interferents

In recent years, growing threat of terrorist attacks with use of chemical or biological warfare agents is observed. Biological agents, due to often delayed effects, higher lethality and more difficult detection and identification compared to chemical agents, are especially dangerous. Therefore, rapid detection and discrimination of dangerous biological materials has become a security aim of considerable importance. Various analytical methods, including FTIR spectroscopy combined with statistical analysis have been used to discriminate various bioagents and their background interferents. The applicability for this purpose of another spectroscopic technique, Surface Enhanced Raman Spectroscopy (SERS), has also been intensively investigated in recent years. In this work, the results of the application of FTIR technique performed in reflectance mode using Horizontal Attenuated Total Reflectance accessory (HATR) for discrimination of vegetative bacteria, bacterial spores and background interferents are discussed. Applied technique is shown to be capable of distinguishing between vegetative bacteria, bacterial spores and fungi against other biological specimens. In addition, the results of initial studies on application of plasmonic nanostructures for enhancement of Raman scattering signals of bacterial cells are discussed. Our studies have shown that it is possible to obtain Raman scattering signal from single bacterial cell in presence of single plasmonic nanostructure.

The effect of artificial seawater on SERS spectra of amino acids-Ag colloids: An experiment of prebiotic chemistry

The large enhancement of signal observed in surface enhanced Raman spectroscopy (SERS) could be helpful for identifying amino acids on the surface of other planets, in particular for Mars, as well as in prebiotic chemistry experiments of interaction minerals/amino acids. This paper reports the effect of several substances (NaCl, MgCl2, KBr, CaSO4, K2SO4, MgSO4, KI, NH4Cl, SrCl2, CaCl2, Na2SO4, KOH, NaOH, H3BO3) on the SERS spectra of colloid of sodium citrate-CSC and colloid of sodium borohydride-CSB. The effect of four different artificial seawaters and these artificial seawaters plus amino acids (α-Ala-alanine, Gly-glycine, Cys-cysteine, AIB-2-aminoisobutiric acid) on SERS spectra using both CSC and CSB was also studied. For CSC, the effect of water, after dilution of the colloid, was the appearance of several absorption bands belonging to sodium citrate in the SERS spectrum. In general, artificial seawaters enhanced several bands in SERS spectra using CSC and CSB and CSC was more sensitive to those artificial seawaters than CSB. The identification of Gly, α-Ala and AIB using CSC or CSB was not possible because several bands belonging to artificial seawaters, sodium citrate or sodium borohydride were enhanced. On the other hand, artificial seawaters did not interfere in the SERS spectra of Cys using CSC or CSB, although the interaction of Cys with each colloid was different. For CSC the band at 2568cm−1 (S–H stretching) of Cys vanished and for CSB the intensity of this band decreased, indicating the –SH of Cys was bonded to Ag to form –S–Ag. Thus SERS spectroscopy could be used for Cys detection on Mars soils using Mars land rovers as well as to study the interaction between Cys and minerals in prebiotic chemistry experiments.

Electrochemical surface-enhanced Raman spectroscopic study of redox processes of solution species at electrode modified with the redox dye Meldola blue

Gold electrodes modified with adsorbed or electropolymerized layers of the redox dye Meldola blue have been prepared and studied by Surface enhanced Raman spectroscopy (SERS) at 785nm laser excitation. The intensity of SERS spectra obtained differ essentially for electrochemically oxidized and reduced layers of MB, both in pH 1.0 and pH 7.0 solutions studied. Electrooxidation of ascorbate at MB modified electrodes in pH 7.0 solution was studied, and it has been shown with in situ SERS spectroscopy that the relative content of oxidized and reduced forms of MB within adsorbed or electropolymerized layer depends on electrode potential and ascorbate concentration. Also, electrooxidation of hydroquinone at MB modified electrodes in pH 1.0 solution has been studied, and the formation of reaction product benzoquinone has been demonstrated with SERS spectroscopy. This process occurs faster at electrode modified with electropolymerized MB, and at higher concentration of hydroquinone.

Generation of Ultralarge Surface Enhanced Raman Spectroscopy (SERS)-Active Hot-Spot Volumes by an Array of 2D Nano-Superlenses

Surface Enhanced Raman Spectroscopy (or SERS) has received tremendous attention in the past three decades. However, the extremely-confined probe volume (1 nm) of the plasmonic hot-spots occurring on a conventional roughened SERS-active metallic surface has limited value in macro-molecular studies. In this article, we show the plausibility of generating large SERS hot-spot volumes on an atomically-flat metal surface based upon a special 3D adiabatic plasmonic nano-focusing effect brought about by an array of nano-scale superlenses. We experimentally demonstrate the feasibility of this particular approach and report, for the first time, the acquisition of whole-protein SERS spectra of a layer of test protein, Cytochrome-c, using a custom-made Otto-Raman spectroscopy system equipped with nano-fluidics. Our study shows the potential of whole-protein SERS spectroscopy as a useful analytical tool that complements surface probe microscopies.

Surface enhanced Raman scattering to study surface contaminants on semiconductors

Abstract This work shows that by using surface enhanced Raman spectroscopy (SERS) it is possible to observe and characterize surface species due to contamination onto semiconductor materials. We detected the presence of surface contaminants on semiconductors by coating the surface with an Ag island film. By means of this technique we were able to observe the Raman bands of these contaminants, enhanced through the surface enhanced scattering mechanism. These results demonstrate the high sensitivity of SERS and suggest surface contaminants can be detected by SERS, even if they are present at very low concentration. This extension of SERS spectroscopy to semiconductor materials is important for developing SERS as a new surface sensitive probe in material science.

Structural differences in self-assembled monolayers of anthraquinone derivatives on silver and gold electrodes studied by cyclic voltammetry and in situ SERS spectroscopy

Self-assembled monolayers (SAMs) of 1-anthraquinonylbutylsulfide (1-AQS) and 2-anthraquinonylbutylsulfide (2-AQS) on silver and gold electrodes were investigated by cyclic voltammetry and in situ surface enhanced Raman spectroscopy (SERS). A reversible redox wave was observed for 1-AQS and the redox potential shifted ca. −30 and −60 mV pH −1 at silver and gold electrodes, respectively, in the pH region 5–9. On silver electrodes, the electrochemical properties of 1-AQS were similar to those of 2-AQS. In addition, the Raman spectrum of 1-AQS powder is very similar in intensity and peak positions to that of 2-AQS powder. However, in situ SERS measurements showed that the 1-AQS molecule was tilted relative to the silver surface normal and no change in its orientation took place between oxidized and reduced forms. The oxidized 2-AQS molecule was shown to be adsorbed perpendicular to the silver surface, but on reduction at −0.6 V the orientation of the anthraquinone plane changed. On gold electrodes, no clear SERS spectrum was obtained for the SAM of 1-AQS, suggesting a flat orientation of the anthraquinone plane relative to the electrode surface. SERS spectra of 2-AQS on the gold surfaces gave clear spectra, suggesting a perpendicular orientation of the anthraquinone plane relative to the gold surface independent of the applied potential. These differences in orientation are ascribed to the position of the butylsulfide moiety on the anthraquinone ring at gold and silver electrodes.

Morphological Study of Metal Colloids Employed as Substrate in the SERS Spectroscopy

Transmission electronic microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize several silver and copper sols employed as substrates in surface enhanced Raman spectroscopy (SERS). In this study we have focused our attention on the changes observed when the large scale roughness is modified by the aggregation agent 1,5-dimethylcytosine (DMC). A previous analysis of several unaggregated silver and copper colloids and a comparison with the corresponding aggregated colloids were made, so that a relationship between the morphology of the aggregates and the SERS results was obtained. Information about the aggregation process of the colloids studied is also presented, on the basis of the results obtained from TEM, UV-visible spectroscopy, and the study of the variation of the SERS signal with the concentration of DMC. From these results, the morphology of the resulting aggregates which yields the most intense SERS signal is inferred. A different aggregation mechanism is suggested for each colloidal metal, according to the remarkably different geometry of the final aggregates observed. This is further attributed to the different sizes of the simple particles present in the original colloids.

Gold surface enhanced Raman spectroscopy of amphiphilic sulfur viologens during electron transfer

Surface enhanced Raman spectroscopy (SERS) was used to characterize electron transfer through mediators present as self-assembled monolayers on gold electrode surfaces. The surface active species were three alkyl sulfides with the general structure: [octadecyl]-S-[CH 2] n -[viologen]-[CH 2] m dibromide, in which n was 5, 7 and 10, and the sum of n and m held constant . These structures thus present the electroactive moiety at varying distances from the surface upon which they are adsorbed. Cyclic voltammetry was used to confirm results of previous measurements on silver, after which SERS spectroelectrochemistry was used to identify the electroactive species formed following the electron transfer steps. Electrochemistry imdicated that electron transfer was inversely proportional to the distance of the viologen from the gold surface; spectroelectrochemistry using SERS corroborated this, as the intensity of Raman scattering in SERS is a function of the distance of a scattering chromophore from the metal surface with which it is associated. Spectra of viologens were obtained for the neutral and radical species. Analysis of these data indicates agreement with the previous purely electrochemical studies of these compounds. These studies extend the utility of SERS spectroscopy for monolayer characterization by using gold surfaces to provide enhancement; silver surfaces have usually been used in previous SERS spectroelectrochemical studies, SERS employing gold surfaces may be especially significant in the case of biological molecules, because excitation in the red spectral regions greatly reduces background fluorescence, and a significantly decreased risk of photodecomposition is assured. For example, observation of gold SERS of chlorophyll or heme proteins by excitation into their Q-bands will permit acquisition of new information regarding these important compounds [cf. 6].