Surface-enhanced Raman Signals Research Articles

Highly sensitive technique for detection of adulterants in centella herbal samples using surface enhanced Raman spectroscopy (SERS)

The trace level detection of adulterants in food, nutritional supplements and medicinal herbs is highly challenging in the field of food processing and herbal industries. In addition, laborious sample processing procedures and well trained personnel are required to analyse the samples using conventional analytical equipments. In this study, a highly sensitive technique with minimal sampling processes and human intervention is proposed for the trace amount detection of pesticidal residues in centella powder. Herein, graphene oxide gold (GO-Au) nanocomposite coated parafilm is developed as substrate by simple dropcasting technique to facilitate dual surface enhanced Raman signal. The dual SERS enhancement involving chemical enhancement from graphene and electromagnetic signal enhancement from gold nanoparticles is utilized for detection of chlorpyrifos in the ppm level concentration. The flexible polymeric surfaces could be the better choice for SERS substrates due to their inherent properties such as flexibility, transparency, roughness and hydrophobicity. Among the various types of flexible substrates explored, GO-Au nanocomposites coated parafilm substrates showed better Raman signal enhancement. Parafilm coated with GO-Au nanocomposites is successful in achieving detection limits down to 0.1 ppm of chlorpyrifos in centella herbal powder sample. Thus, the fabricated parafilm based GO-Au SERS substrates could be used as a screening tool at quality control of herbal product manufacturing sectors for trace level detection of adulterants in herbal samples from their unique chemical and structural information.

Facile All-Optical Method for In Situ Detection of Low Amounts of Ammonia.

SummaryAs a key precursor for nitrogenous compounds and fertilizer, ammonia affects our lives in numerous ways. Rapid and sensitive detection of ammonia is essential, both in environmental monitoring and in process control for industrial production. Here we report a novel and nonperturbative method that allows rapid detection of ammonia at low concentrations, based on the all-optical detection of surface-enhanced Raman signals. We show that this simple and affordable approach enables ammonia probing at selected regions of interest with high spatial resolution, making in situ and operando observations possible.

Magnetic and silver nanoparticle functionalized calcium carbonate particles—Dual functionality of versatile, movable delivery carriers which can surface-enhance Raman signals

Multifunctional probes play an increasing role even beyond applications in biomedicine. Multifunctionality introduced by the dual types of complementary probes is always attractive because, in this case, functionalized objects inherit the function of both materials. Porous calcium carbonate microparticles are becoming popular carriers of biomolecules and biosensors, as well as imaging enhancers. We demonstrate here a dual function of these carriers by incorporating both magnetic and silver nanoparticles. Magnetic nanoparticles enable movements and displacements by a magnetic field, while silver nanoparticles provide surface-enhanced Raman signal amplification necessary for the detection of biomolecules. Application of such dual-functional carriers is foreseen beyond the applications of biomedicine and theranostics.

Distorted Phthalocyanines by Click Chemistry: Photoacoustic, Photothermal, and Surface-Enhanced Resonance Raman Studies.

Distortion of nominally planar phthalocyanine macrocycles affects the excited state dynamics in that most of the excited-state energy decays through internal conversion. A click-type annulation reaction on a perfluorophthalocyanine platform appending a seven-membered ring to the β-positions on one or more of the isoindoles distorts the macrocycle and modulates solubility. The distorted derivative enables photoacoustic imaging, photothermal effects, and strong surface-enhanced resonance Raman signals.

Enzyme-Driven Switchable Fluorescence-SERS Diagnostic Nanococktail for the Multiplex Detection of Lung Cancer Biomarkers.

Comprehensive profiling of multiple protein targets plays a critical role in deeper understanding of specific disease conditions associated with high heterogeneity and complexity. Herein, we present the design and fabrication of smart programmable nanoarchitectures, which could integrate clinically relevant diagnostic modalities for the multiplexed detection of most prevalent panel of disease biomarkers present in lung cancer. The multiplex nanoprobes were prepared by attaching dual-functional Raman-active fluorogens onto spherical gold nanoparticles through a peptide linker, Phe-Lys-Cys (FKC), which is engineered with a cathepsin B (cathB) enzyme cleavage site. The presence of cathB induces the scission of FKC upon homing into the cancer cells, resulting in the release of the initially latent fluorophores with a concomitant quenching of the surface-enhanced Raman signal intensity, thereby realizing an on-off switching between the fluorescence and Raman modalities. The enzyme-triggered switchable nanoprobes were utilized for the simultaneous detection of pathologically relevant lung cancer targets by tethering with specific antibody units. The multiplex-targeted multicolor coded detection capability of the antitags was successfully developed as a valid protein screening methodology, which can address the unmet challenges in the conventional clinical scenario for the precise and early diagnosis of lung cancer.

SERS detection of 4-Aminobenzenethiol based on triangular Au-AuAg hierarchical-multishell nanostructure

The surface-enhanced Raman signals of 4-Aminobenzenethiol (4-ABT) adsorbed on the surface of triangular Au-AuAg hierarchical-multishell nanostructure have been investigated. Here, the approach to produce core-cavity-shell sandwich nanostructures presented as Au-AuAg is the same as preparing metal nanoparticles with hollow morphology, in which the galvanic replacement reaction takes place between silver and chloroauric acid. In this paper, we directly mix 4-ABT with gold nanoparticles and drop it on glass slides to study the effect of nanoparticles on signal enhancement of Raman spectrum, avoiding the cumbersome process of preparing metal-molecular-metal three-layer structure as reported. A significant increase in the SERS intensity of b2 mode around 1140 cm−1 was observed, which could quantify the concentration of 4-ABT indirectly. In a certain range, the Raman intensity gradually increases with the increasing intermediate gap, which has a strong relationship with dipole plasmon hybridization of core-dielectric-shell sandwich nanostructure. Moreover, Raman spectrum results show that the Au-AuAg substrate can produce signal intensity about 3.8 × 102 times stronger than that of 4-ABT alone and the detection limit was as low as 0.1 μM in solution.

High Electromagnetic Field Enhancement of TiO2 Nanotube Electrodes.

We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface-enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b5 were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non-directly surface-interacting probes, for which the involvement of charge-transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode.

Monitoring of betulin nanoemulsion treatment and molecular changes in mouse skin cancer using surface enhanced Raman spectroscopy

The aim of this study was to obtain in vivo and ex vivo reproducible surface enhanced Raman signal from mouse skin and to use it for the differentiation of skin pathologies. We induced skin carcinoma in mice models using a chemical treatment and tested the chemopreventive activity of a new formulation based on natural compound betulin extracted from the bark of birch trees. Using surface enhanced Raman spectroscopy (SERS) we identified in vivo and ex vivo the spectral signatures characteristic to the healthy skin, melanoma skin induced in mouse models, and to the pathology evolution when the betulin nanoemulsion formulation was topically applied on the cancerous skin of mice. SERS markers associated to each pathology were identified and the signal was distinguished from the classical Raman signal of skin based on several biomarkers, such as the disappearance of the amide I band of proteins, the amplification of the 1574 cm−1 band assigned to nucleic acid bases, and the appearance of the highly amplified band at 230 cm−1 characteristic to the metal-biomolecules complex. The various skin pathologies were differentiated using principal components analysis and K-means clustering. The effectiveness of the betulin nanoemulsion treatment was validated by the histological examination and the chemometrics methods, which successfully confirmed the direct SERS differentiation between the cancerous and the betulin nanoemulsion treated skin.

Raman probe based on hollow-core microstructured fiber

Surface-enhanced Raman scattering (SERS) technology can effectively enhance the Raman signal of sample molecules. It has a higher sensitivity to detect biomolecule and thus has many potential applications in biochemistry. The combination of hollow-core microstructured fiber and SERS technology not only enables remote real-time and distributed detection, but also can increase the effective action area between the light field and the object to be measured, and further reduce silica glass background signal that is unavoidable in traditional fiber probes. In this paper, the hollow-core microstructure fiber Raman probes with excellent performance are investigated from the aspects of fiber preparation and SERS experi-mental testing. First, we design and manufacture a kind of hollow-core microstructured fiber with multi-bands in the visible and near-infrared wavelength. The fibers show good light guide performance and thus can fully meet the requirements for surface-enhanced Raman excitation and signal transmission. At the same time, the large core size facilitates the coupling of excitation light, and provides enough room for the test object and the light field. Then, this hollow-core microstructured fiber is used in surface-enhanced Raman experiment. A layer of nano-Ag film is modified on the inner surface of the hollow-core microstructure fiber to prepare the SERS probe by the vacuum physical sputtering method, and Rhodamine 6G (R6G) alcohol solutions with different concentrations are prepared by the dilution method. The hollow-core microstructured fiber deposited with the Ag nano-film is immersed in R6G alcohol solution for 2 min. The alcohol solution of R6G is sucked into the air hole of the hollow-core microstructured fiber by the capillary effect. Then this fiber with R6G alcohol solution is placed in a drying oven at 40 ℃ for 3 h until the alcohol solvent in the air hole is completely volatilized. After that, this fiber is taken out and tested under a detection environment full with air. The fiber SERS probes are tested by microscopic confocal Raman spectroscopy, then the Raman spectra of R6G alcohol solvents with different concentrations are obtained. An R6G Raman signal with a concentration as low as 10-9 mol/L is successfully detected on the front side of the probe. In the far-end back-side detection mode, the detected concentration of SERS probe can be less than 10-6 mol/L. The designed hollow-core microstructured fiber probe has a simple structure and is easy to prepare and test. Compared with the traditional optical fiber, it has advantages of large effective area for the test object and the light field, small interference from the silica glass background signal. This hollow-core microstructured fiber probe has wide application prospects in biochemical detection and other fields.

A sensitive Galvanic replacement reaction-SERS method for Au(III) with Victoria blue B molecular probes in silver nanosol substrate

Stable silver nanosol (AgNP) was prepared by the light-wave procedure. Based on the Galvanic replacement reaction (GRR) of Au(III) on AgNP surface and using Victoria blue B (VBB) as molecular probes, a surface-enhanced Raman scattering (SERS) quantitative analysis of trace Au(III) was developed. VBB has no SERS signal in the dispersed AgNP sol substrate. Addition of NaCl, the VBB produced strong surface-enhanced Raman signals at 1381cm−1 in the aggregated AgNP sol substrate. When Au(III) is present in the system, the surface Ag atoms interact with Au(III) to form Ag+ and Au due to the potential difference, and the Au atom and AgCl deposited on the AgNP surface to reduce the SERS activity significantly and result in SERS signal quenching. The quenched SERS signal is linear to Au(III) concentration in the range of 25–625nmol/L, with a detection limit of 8nmol/L. The GRR system can be also monitored by resonance Rayleigh scattering (RRS) spectroscopy, Au can be detected by SERS and RRS methods, and the former is more sensitive.

Engineering microscale two-dimensional gold nanoparticle cluster arrays for advanced Raman sensing: An AFM study

We realized and tested a strategy for developing reproducible and stable two-dimensional gold nanoparticle cluster arrays arranged on silicon substrates, to be used for surface-enhanced Raman spectroscopy. We combined electron beam lithography and molecular functionalization to finely control the shape of the nanoparticle assemblies. Atomic force microscopy analysis allowed to optimize the procedure of nanoparticle cluster array fabrication in terms of electron beam dose and chemical protocol, enabling to achieve a good regularity in spacing and size (i.e. area and layer number) of the clusters. MicroRaman space resolved measurements were undertaken on large 2D arrays (100 × 100 μm2) made up of regularly microsized clusters. The high surface enhanced Raman signal measured on the structures highlights the full correspondence of the spatial and optical periodicity achieved. This standardized procedure represent the basis to realize versatile platforms for nano-optical investigation and towards an efficient high-sensitive multiplex sensing.

Surface-Enhanced Raman Spectroscopy Study of 4-ATP on Gold Nanoparticles for Basal Cell Carcinoma Fingerprint Detection

The surface-enhanced Raman signals of 4-aminothiophenol (4-ATP) attached to the surface of colloidal gold nanoparticles with size distribution of 2 to 5 nm were used as a labeling agent to detect basal cell carcinoma (BCC) of the skin. The enhanced Raman band at 1075 cm-1 corresponding to the C-S stretching vibration in 4-ATP was observed during attachment to the surface of the gold nanoparticles. The frequency and intensity of this band did not change when the colloids were conjugated with BerEP4 antibody, which specifically binds to BCC. We show the feasibility of imaging BCC by surface-enhanced Raman spectroscopy, scanning the 1075 cm-1 band to detect the distribution of 4ATP-coated gold nanoparticles attached to skin tissue ex vivo.

HD DVD substrates for surface enhanced Raman spectroscopy analysis: fabrication, theoretical predictions and practical performance

Commercially available HD-DVD templates have been used to theoretically predict the occurrence of surface plasmons supermodes which improve the detection of surface enhanced Raman signals.

Hierarchical Nanoflowers on Nanograss Structure for a Non-wettable Surface and a SERS Substrate.

Hierarchical nanostructures of CuO nanoflowers on nanograss were investigated for self-cleaning and surface plasmonic applications. We achieved the hierarchical nanostructures using one-step oxidation process by controlling the formation of flower-like nanoscale residues (nanoflowers) on CuO nanograss. While the nanograss structure of CuO has a sufficient roughness for superhydrophobic characteristics, the additional hierarchy of nanoflowers on nanograss leads to a semi-reentrant structure with a high repellency even for a very small droplet (10 nL) of low surface tension liquid such as 25 % ethanol (~35 mN/m), thus providing non-wettable and self-cleaning properties. Furthermore, the CuO hierarchical nanostructure serves as a substrate for surface-enhanced Raman spectroscopy (SERS). Both of the CuO nanograss and nanoflower provide many nanoscale gaps that act as hot-spots for surface-enhanced Raman signal of 4-mercaptopyridine (4-Mpy), thus enabling a non-destructive detection in a short analysis time with relatively simple preparation of sample. Especially, the CuO nanoflower has larger number of hot-spots at the nanogaps from floral leaf-like structures, thus leading to three times higher Raman intensity than the CuO nanograss. These multifunctional results potentially provide a path toward cost-effective fabrication of a non-wettable surface for self-maintenance applications and a SERS substrate for sensing applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1214-7) contains supplementary material, which is available to authorized users.

Aggregation induced Raman scattering of squaraine dye: Implementation in diagnosis of cervical cancer dysplasia by SERS imaging.

The extent of squaraine dye aggregation that reflects on surface enhanced Raman signal scattering (SERS) intensity upon adsorption on nano-roughened gold surface has been investigated. Here we have synthesized a serious of six squaraine dyes consisting of two different electron donor moiety i.e. 1,1,2-trimethyl-1H-benzo[e]indole and 2-methylbenzo[d]thiazole which modulates the chemisorptions and hydrophobicity being designated as SQ1, SQ2, SQ3, SQ4, SQ5 and SQ6. Interestingly, SQ2 (mono lipoic acid appended), SQ5 and SQ6 (conjugated with hexyl and dodecyl side chain) squaraine derivatives having more tendency of aggregation in DMSO-water mixed solvent showed significant increase of Raman scattering in the fingerprint region when chemisorbed on spherical gold nanoparticles. Two sets of SERS nanotags were prepared with colloidal gold nanoparticle (Au-NPs size: 40 nm) by incorporating Raman reporters SQ2 and SQ5 followed by thiolated PEG encapsulation (SH-PEG, SH-PEG-COOH) denoted as AuNPs-SQ2-PEG and AuNPs-SQ5-PEG. Further conjugation of these nanotag with monoclonal antibodies specific to over expressed receptors, EGFR and p16/Ki-67 in cervical cancer cell, HeLa showed prominent SERS mapping intensity and selectivity towards cell surface and nucleus. The fast and accurate recognition obtained by antibody triggered SERS-nanotag has been compared with conventional time consuming immunocytochemistry technique which prompted us to extend further investigation using real patient cervical smear sample for a non-invasive, ultrafast and accurate diagnosis.

Mild temperature synthesis of gold nanoplates using polyethyleneimine and their improved surface enhanced Raman signal

This study explores the facile controlled-synthesis and localized surface plasmonic properties of Au nanoplates. Au nanoplates were synthesized via a reaction of HAuCl4 with branched polyethyleneimine (BPEI) in the presence of urea at a reaction temperature as low as 30 °C. Structural characterizations revealed that the synthesized Au nanoplates had an average lateral size of around 2–8 μm and a thickness of around 40 nm, plus they were highly crystalline in spite of the low reaction temperature. Studies of the growth factors for Au nanoplates showed that the PEI morphology, molar ratio of BPEI/HAuCl4, pH of the reaction solution, and concentration of urea all played important roles in the formation of thin Au nanoplates. With a low BPEI/HAuCl4 ratio or under acidic conditions, thick Au plates were synthesized, whereas Au nanoparticles around 10–20 nm were observed with a high BPEI/HAuCl4 ratio or under basic conditions. When the synthesis was conducted in the absence of urea, thick Au nanoplates were synthesized, indicating that urea can serve as a capping agent for thin Au nanoplates. The resulting Au nanoplates also exhibited an enhanced surface-enhanced Raman scattering (SERS) signal when compared with Au nanoparticles due to their sharp corners and edges.

Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy with Picosecond Excitation.

Tip-enhanced Raman spectroscopy (TERS) provides chemical information about adsorbates with nanoscale spatial resolution, but developments are still required in order to incorporate ultrafast temporal resolution. In this Letter, we demonstrate that a reliable TER signal of rhodamine 6G (R6G) using picosecond (ps)-pulsed excitation can be obtained in ultrahigh vacuum (UHV). In contrast to our previous observation of irreversible signal loss in ambient TERS ( Klingsporn , J. M. ; Sonntag , M. D. ; Seideman , T. ; Van Duyne , R. P. J. Phys. Chem. Lett. 2014 , 5 , 106 - 110 ), we demonstrate that the UHV environment decreases irreversible signal degradation. As a complement to the TERS experiments, we examined the rate of surface-enhanced Raman (SER) signal decay under picosecond irradiation and found that it is also slowed in UHV compared to that in ambient. Signal decay kinetics suggest that the predominant mechanism responsible for signal loss in ps SERS of R6G is surface diffusion. Both diffusive and reactive phenomena can lead to pulsed excitation TER signal loss, and a UHV environment is advantageous in either scenario.

ChemInform Abstract: Plasmonic Nanomaterials for Biodiagnostics

AbstractReview: 50 refs.

Plasmonic nanomaterials for biodiagnostics

The application of nanomaterials to detect disease biomarkers is giving rise to ultrasensitive assays, with scientists exploiting the many advantageous physical and chemical properties of nanomaterials. The fundamental basis of such work is to link unique phenomena that arise at the nanoscale to the presence of a specific analyte biomolecule, and to modulate the intensity of such phenomena in a ratiometric fashion, in direct proportion with analyte concentration. Precise engineering of nanomaterial surfaces is of utmost importance here, as the interface between the material and the biological environment is where the key interactions occur. In this tutorial review, we discuss the use of plasmonic nanomaterials in the development of biodiagnostic tools for the detection of a large variety of biomolecular analytes, and how their plasmonic properties give rise to tunable optical characteristics and surface enhanced Raman signals. We put particular focus on studies that have explored the efficacy of the systems using physiological samples in an effort to highlight the clinical potential of such assays.

Counting Molecules with a Mobile Phone Camera Using Plasmonic Enhancement

Plasmonic field enhancement enables the acquisition of Raman spectra at a single molecule level. Here we investigate the detection of surface enhanced Raman signal using the unmodified image sensor of a smart phone, integrated onto a confocal Raman system. The sensitivity of a contemporary smart phone camera is compared to a photomultiplier and a cooled charge-coupled device. The camera displays a remarkably high sensitivity, enabling the observation of the weak unenhanced Raman scattering signal from a silicon surface, as well as from liquids, such as ethanol. Using high performance wide area plasmonic substrates that enhance the Raman signal 106 to 107 times, blink events typically associated with single molecule motion, are observed on the smart phone camera. Raman spectra can also be collected on the smart phone by converting the camera into a low resolution spectrometer with the inclusion of a collimator and a dispersive optical element in front of the camera. In this way, spectral content of the bli...