Simultaneous Photoluminescence and SERS Observation of Nanodiamond at Laser Deposition on Noble Metals

The metal-modified luminescence and surface-enhanced Raman scattering (SERS) occurring near nanostructured surfaces of noble metals recently have been observed for different kinds of nanocrystals associated with the metal nanostructures. In the present work, the photoluminescence and Raman scattering of diamond nanocrystals of sizes 100 and 300 nm patterned on Ag and Au thin nanostructured films via laser accelerated deposition using a femtosecond laser are discussed. The laser accelerated deposition forms ordered periodical nanodiamond–metal nanostructures and allows adjusting the interaction between nanodiamond and metal by varying the laser acceleration parameters as well as by using different metals (Ag and Au), and varying the structure of the metal film. Correspondingly, the spectroscopic properties of the system determined by interaction between nanoparticles and metal are tuned. The enhancement of nanodiamond photoluminescence together with SERS of graphite fraction and disordered carbon of nanodiamonds are observed for nanodiamond–Ag structures at 488- and 532-nm excitations, while for the nanodiamond–Au structure some characteristic SERS effects are observed at 785-nm excitation. The mechanisms of enhancement are discussed considering the nanodiamond–metal interaction and laser acceleration effect on nanodiamond.     

Biological synthesis of gold nanowires using extract of Rhodopseudomonas capsulata

An environmentally friendly method using a cell-free extract (CFE) of Rhodopseudomonas capsulata is proposed to synthesize gold nanowires with a network structure. This procedure offers control over the shapes of gold nanoparticles with the change of HAuCl4 concentration. The CFE solutions were added with different concentrations of HAuCl4, resulting in the bioreduction of gold ions and biosynthesis of morphologies of gold nanostructures. It is probable that proteins acted as the major biomolecules involved in the bioreduction and synthesis of gold nanoparticles. At a lower concentration of gold ions, exclusively spherical gold nanoparticles with sizes ranging from 10 to 20 nm were produced, whereas gold nanowires with a network structure formed at the higher concentration of gold ions in the aqueous solution. This method is expected to be applicable to the synthesis of other metallic nanowires such as silver and platinum, and even other anisotropic metal nanostructures are expected using the biosynthetic methods.     

A Paper-Fiber-Supported 3D SERS Substrate

Plasmonics - Surface-enhanced Raman scattering (SERS) spectroscopy is an effective approach for trace-level detection of molecular substance. Plasmonic metallic nanostructures with high...     

Direct Fabrication Route to Plastic-Supported Gold Nanoparticles for Flexible NIR-SERS

Stable gold nanoparticles with surface plasmon resonance tunable from visible (Vis) to near-infrared (NIR) are deposited via a direct sputtering methodology on large area polyethylene terephthalate (PET) to be used as effective, flexible NIR surface-enhanced Raman scattering (SERS) substrates. An O₂ plasma treatment of PET is used to tailor growth dynamics, geometry, and plasmonic properties of nanoparticles. The O₂ plasma treatment of PET results also in effective improvement of nanoparticle anchoring on the plastic substrate, providing more stable, flexible SERS systems. The functionality of fabricated SERS substrates has been tested using benzylthiol, and SERS enhancement factors in the range 10⁴ have been achieved, which are comparable with those reported in literature for gold nanostructures fabricated on silicon substrate. These results attest the great potentiality of this methodology for the production of cost-effective flexible and reusable large-scale SERS substrates.     

Single cell analysis using surface enhanced Raman scattering (SERS) tags

Fluorescence is a mainstay of bioanalytical methods, offering sensitive and quantitative reporting, often in multiplexed or multiparameter assays. Perhaps the best example of the latter is flow cytometry, where instruments equipped with multiple lasers and detectors allow measurement of 15 or more different fluorophores simultaneously, but increases beyond this number are limited by the relatively broad emission spectra. Surface enhanced Raman scattering (SERS) from metal nanoparticles can produce signal intensities that rival fluorescence, but with narrower spectral features that allow a greater degree of multiplexing. We are developing nanoparticle SERS tags as well as Raman flow cytometers for multiparameter single cell analysis of suspension or adherent cells. SERS tags are based on plasmonically active nanoparticles (gold nanorods) whose plasmon resonance can be tuned to give optimal SERS signals at a desired excitation wavelength. Raman resonant compounds are adsorbed on the nanoparticles to confer a unique spectral fingerprint on each SERS tag, which are then encapsulated in a polymer coating for conjugation to antibodies or other targeting molecules. Raman flow cytometry employs a high resolution spectral flow cytometer capable of measuring the complete SERS spectra, as well as conventional flow cytometry measurements, from thousands of individual cells per minute. Automated spectral unmixing algorithms extract the contributions of each SERS tag from each cell to generate high content, multiparameter single cell population data. SERS-based cytometry is a powerful complement to conventional fluorescence-based cytometry. The narrow spectral features of the SERS signal enables more distinct probes to be measured in a smaller region of the optical spectrum with a single laser and detector, allowing for higher levels of multiplexing and multiparameter analysis.     

In vivo tumor targeting and spectroscopic detection with surface-enhanced Raman nanoparticle tags

We describe biocompatible and nontoxic nanoparticles for in vivo tumor targeting and detection based on pegylated gold nanoparticles and surface-enhanced Raman scattering (SERS). Colloidal gold has been safely used to treat rheumatoid arthritis for 50 years, and has recently been found to amplify the efficiency of Raman scattering by 14-15 orders of magnitude. Here we show that large optical enhancements can be achieved under in vivo conditions for tumor detection in live animals. An important finding is that small-molecule Raman reporters such as organic dyes were not displaced but were stabilized by thiol-modified polyethylene glycols. These pegylated SERS nanoparticles were considerably brighter than semiconductor quantum dots with light emission in the near-infrared window. When conjugated to tumor-targeting ligands such as single-chain variable fragment (ScFv) antibodies, the conjugated nanoparticles were able to target tumor biomarkers such as epidermal growth factor receptors on human cancer cells and in xenograft tumor models.     

Differently Environment Stable Bio-Silver Nanoparticles: Study on Their Optical Enhancing and Antibacterial Properties

Generally, limited research is extended in studying stability and applicational properties of silver nanoparticles (Ag NPs) synthesized by adopting ‘green chemistry’ protocol. In this work, we report on the synthesis of stable Ag NPs using plant-derived materials such as leaf extract of Neem (Azadirachta indica) and biopolymer pectin from apple peel. In addition, the applicational properties of Ag NPs such as surface-enhanced Raman scattering (SERS) and antibacterial efficiencies were also investigated. As-synthesized nanoparticles (NPs) were characterized using various instrumentation techniques. Both the plant materials (leaf extract and biopolymer) favored the synthesis of well-defined NPs capped with biomaterials. The NPs were spherical in shape with an average particle size between 14-27 nm. These bio-NPs exhibited colloidal stability in most of the suspended solutions such as water, electrolyte solutions (NaCl; NaNO₃), biological solution (bovine serum albumin), and in different pH solutions (pH 7; 9) for a reasonable time period of 120 hrs. Both the bio-NPs were observed to be SERS active through displaying intrinsic SERS signals of the Raman probe molecule (Nile blue A). The NPs were effective against the Escherichia coli bacterium when tested in nutrient broth and agar medium. Scanning and high-resolution transmission electron microscopy (SEM and HRTEM) images confirmed cellular membrane damage of nanoparticle treated E. coli cells. These environmental friendly template Ag NPs can be used as an antimicrobial agent and also for SERS based analytical applications.     

Oligonucleotide-Mediated Au–Ag Core–Shell Nanoparticles

The bimetallic core–shell nanoparticles show unique plasmonic properties and their preparations and characterizations are currently under investigation. A new type of Au core–Ag shell (Au@Ag) nanoparticles is prepared by sandwiching the chemically attached Raman reporter molecules (RRMs) and a 12-base-long oligonucleotide between the 13 nm average size core-gold nanoparticles (AuNPs) and 9 nm and 21 nm average size of Ag shell. The synthesized Au@Ag nanoparticles are tested for their surface-enhanced Raman scattering (SERS) performance. It is found that the chemical attachment of the oligonucleotides along with the RRM improved the enhancement in Raman scattering more than one order of the magnitude with the Au@Ag nanoparticles with an average 9-nm shell thickness while the Au@Ag nanoparticles with 21 nm average shell thickness have poor SERS activity. A minimum enhancement factor of 1.0 × 10⁷ is estimated for the SERS active oligonucleotide-mediated Au@Ag nanoparticles. The approach may provide new routes for preparation of highly sensitive new generation of bimetallic core–shell nanoparticles.     

Self-Organized Ag Nanorings Antenna Substrates for Surface-Enhanced Raman Spectroscopy

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.     

Label free sub-picomole level DNA detection with Ag nanoparticle decorated Au nanotip arrays as surface enhanced Raman spectroscopy platform

Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms.     

Facile synthesis of Raman active phospholipid gold nanoparticles

Gold nanoparticle-based surface-enhanced Raman scattering (SERS) probes have shown promise for disease detection and diagnosis. To improve their structural and functional stability for in vivo applications, we synthesized a colloidal SERS gold nanoparticle that encapsulates Raman molecules adsorbed on 60 nm gold with a nonthiol phospholipid coating. Transmission electron microscopy and Raman and UV spectroscopy validated its reproducibility and stability. This novel lipid-based SERS probe provides a viable alternative to the PEGylation and silica coating strategies.     

Surface enhanced Raman scattering for narcotic detection and applications to chemical biology

Raman spectroscopy is rapidly finding favour for applications in the life science because of the ease with which it can be used to extract significant data from tissue and cells. However, the Raman effect is an inherently weak effect, which hinders the analysis of low concentration analytes. Raman sensitivity can be improved via the surface enhanced Raman scattering (SERS) effect. In SERS, Raman spectra are dramatically amplified when a molecule is adsorbed onto nano-roughened noble metal surfaces such as silver and gold. The degree of enhancement enables single-molecule detection, which offers the potential for the unambiguous identification of analytes at concentrations that are useful in both a forensic and a chemical biology context. Here we discuss some of the practical applications of SERS to both low-level narcotic detection, and how this can be applied to chemical biology.     

A Shape-Engineered Surface-Enhanced Raman Scattering Optical Fiber Sensor Working from the Visible to the Near-Infrared

Surface-enhanced Raman scattering (SERS) takes advantage of the giant electromagnetic field enhancement provided by localized surface plasmons in metal nanoparticles to amplify the weak Raman scattering of the molecules. Optical fibers coated with noble metal nanoparticles can therefore be used as SERS-based sensors for remote detection of molecular species. In this article, we report on the development of an optical fiber SERS sensor capable to operate on a range of excitation wavelengths from the visible to the near-infrared. We introduce a quasistatic chemical etching protocol to engineer the tip shape and investigate the effects of the tip shape on the sensor performances.     

Nano-patterned SERS substrate: application for protein analysis vs. temperature

We have illustrated the fabrication of nano-structures as a surface enhanced Raman scattering (SERS) substrate using electro-plating and electron-beam lithography techniques to obtain an array of gold nanograin-aggregate structures of diameter ranging between 80 and 100 nm with interstitial gap of 10-30 nm. The nanostructure based SERS substrate permits us to have better control and reproducibility on generation of plasmon polaritons. The calculation shows the possible detection of myoglobin concentration down to attomole. This SERS substrate is used to investigate the structural changes of different proteins; lysozyme, ribonuclease-B, bovin serum albumin and myoglobin in the temperature range between -65 and 90 degrees C. The in-depth analysis even for small conformational changes is performed using 2D Raman correlation analysis and difference Raman analysis in order to gain straightforward understanding of proteins undergoing thermodynamical perturbation.     

Bare laser‐synthesized Au‐based nanoparticles as nondisturbing surface‐enhanced Raman scattering probes for bacteria identification

The ability of noble metal‐based nanoparticles (NPs) (Au, Ag) to drastically enhance Raman scattering from molecules placed near metal surface, termed as surface‐enhanced Raman scattering (SERS), is widely used for identification of trace amounts of biological materials in biomedical, food safety and security applications. However, conventional NPs synthesized by colloidal chemistry are typically contaminated by nonbiocompatible by‐products (surfactants, anions), which can have negative impacts on many live objects under examination (cells, bacteria) and thus decrease the precision of bioidentification. In this article, we explore novel ultrapure laser‐synthesized Au‐based nanomaterials, including Au NPs and AuSi hybrid nanostructures, as mobile SERS probes in tasks of bacteria detection. We show that these Au‐based nanomaterials can efficiently enhance Raman signals from model R6G molecules, while the enhancement factor depends on the content of Au in NP composition. Profiting from the observed enhancement and purity of laser‐synthesized nanomaterials, we demonstrate successful identification of 2 types of bacteria (Listeria innocua and Escherichia coli). The obtained results promise less disturbing studies of biological systems based on good biocompatibility of contamination‐free laser‐synthesized nanomaterials.

     

Electromagnetic Enhancement Effect Caused by Aggregation on SERS-Active Gold Nanoparticles

We report a morphology-correlated surface-enhanced Raman scattering (SERS) from molecules on the surface of individual clusters of gold nanoparticles of two types and compare the signal from clusters of two, three, four, and five nanoparticles with the signal from single particles. Cluster geometry and particle morphology are determined from transmission electron microscopy for both clusters of 78- to 133-nm nanospheres and clusters of ~250-nm-etched cylindrical particles with crevices and sharp edges, formed in templates. Scattering from molecules on etched cylinders, but not spheres, is sufficiently strong to allow spectra to be collected from single particles illuminated at 632.8 nm. SERS intensities from clusters of cylinders are found to scale linearly with particle number, whereas, for nanospheres, the scaling is non-linear. The linear scaling of SERS from cylinders is a reflection of the high enhancement provided by the sharp features of the individual particles; whereas, the non-linear scaling of SERS from clusters of spheres is found to be consistent with the near-field enhancement from inter-particle coupling simulated for clusters of spheres arranged in representative-observed geometries.     

Optical Absorption in Overcoats of Nanoparticle Arrays on a Metallic Substrate

Surface plasma oscillations in metallic particles as well as in thin metallic films have been studied extensively in the past decades. New features regarding surface plasma excitations are, however, constantly discovered, leading, for example, to surface-enhanced Raman scattering studies and enhanced optical transmission though metal films with nanohole arrays. In the present work, the role of a metallic substrate is examined in two cases, one involving an overcoat of dielectric nanoparticles and the other an overcoat of metallic nanoparticles. Theoretical results are obtained by modeling the nanoparticles as forming a two-dimensional, hexagonal lattice of spheres. The scattered electromagnetic field is then calculated using a variant of the Green function method. Comparison with experimental results is made for nanoparticles of tungsten oxide and tin oxide deposited on either gold or silver substrates, giving qualitative agreement on the extra absorption observed when the dielectric nanoparticles are added to the metallic surfaces. Such absorption would be attributed to the mirror image effects between the particles and the substrate. On the other hand, calculations of the optical properties of silver or gold nanoparticle arrays on a gold or a silver substrate demonstrate very interesting features in the spectral region from 400 to 1,000 nm. Interactions between the nanoparticle arrays surface plasmons and their images in the metallic substrate would be responsible for the red shift observed in the absorption resonance. Moreover, effects of particle size and ambient index of refraction are studied, showing a great potential for applications in biosensing with structures consisting of metallic nanoparticle arrays on metallic substrates.     

Biosynthesis of extracellular and intracellular gold nanoparticles by Aspergillus fumigatus and A. flavus

Green chemistry is a boon for the development of safe, stable and ecofriendly nanostructures using biological tools. The present study was carried out to explore the potential of selected fungal strains for biosynthesis of intra- and extracellular gold nanostructures. Out of the seven cultures, two fungal strains (SBS-3 and SBS-7) were selected on the basis of development of dark pink colour in cell free supernatant and fungal beads, respectively indicative of extra- and intracellular gold nanoparticles production. Both biomass associated and cell free gold nanoparticles were characterized using X-ray diffractogram (XRD) analysis and transmission electron microscopy (TEM). XRD analysis confirmed crystalline, face-centered cubic lattice of metallic gold nanoparticles along with average crystallite size. A marginal difference in average crystallite size of extracellular (17.76 nm) and intracellular (26 and 22 nm) Au-nanostructures was observed using Scherrer equation. In TEM, a variety of shapes (triangles, spherical, hexagonal) were observed in both extra- and intracellular nanoparticles. 18S rRNA gene sequence analysis by multiple sequence alignment (BLAST) indicated 99 % homology of SBS-3 to Aspergillus fumigatus with 99 % alignment coverage and 98 % homology of SBS-7 to Aspergillus flavus with 98 % alignment coverage respectively. Native-PAGE and activity staining further confirmed enzyme linked synthesis of gold nanoparticles.     

Spectroscopy on the wing: Naturally inspired SERS substrates for biochemical analysis

We show that naturally occurring chitinous nanostructures found on the wings of the Graphium butterfly can be used as substrates for surface‐enhanced Raman scattering when coated with a thin film of gold or silver. The substrates were found to exhibit excellent biocompatibility and sensitivity, making them ideal for protein assaying. An assay using avidin/biotin binding showed that the substrates could be used to quantify protein binding directly from changes in the surface‐enhanced Raman scattering (SERS) spectra and were sensitive over a concentration range comparable with a typical enzyme‐linked immunosorbent assays (ELISA) assay. A biomimetic version of the wing nanostructures produced using a highly reproducible, large‐scale fabrication process, yielded comparable enhancement factors and biocompatibility. The excellent biocompatibility of the wings and biomimetic substrates is unparalleled by other lithographically produced substrates, and this could pave the way for widespread application of ultrasensitive SERS‐based bioassays. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Feature‐based recognition of Surface‐enhanced Raman spectra for biological targets

We propose and compare multiple approaches to automatically process data measured through surface‐enhanced Raman scattering (SERS), in the context of intracellular molecule probing. It relies on locally detecting the most relevant spectra to retrieve all data independently through indexing, thus avoiding any pre‐filtering which occurs with standard processing methods. We first assess our approach on simulated data of the spectrum of Rhodamine 6G, and then validate high‐performing methods on experimental measurements of this compound. The optimized method is then utilized to extract and classify the complex SERS response behavior of gold nanoparticles taken in live cells. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)