Hollow Palladium‐Gold Nanochains with Periodic Concave Structures as Superior ORR Electrocatalysts and Highly Efficient SERS Substrates

Unique palladium‐gold hollow nanochains (PdAu HCs) with 1D architecture and an ultrathin Pd‐rich skin exhibit fantastic oxygen reduction reaction (ORR) enhancements due to their high conductivity, structural stability, and maximized atomic utilization. More importantly, such PdAu HCs possess periodic concave structures that boost ORR performance. These structures readily form high‐density high‐index facets, and fewer arc edges. Concave structures can deliver strong strain effects and surface charge accumulation is revealed by off‐axis electron holography. In addition, periodic concave structures can provide strong localized surface–plasmon coupling, which means that PdAu HCs have great potential as efficient surface‐enhanced Raman scattering (SERS) substrates. This study offers a novel and general approach for the design of complex noble metal‐based nanostructures as efficient ORR catalysts and SERS substrates.     

Fabrication of Silver Chevron Arrays as an Efficient and Stable SERS Substrate: Implications in Biological Sensing

Plasmonics - Although glancing angle deposited silver substrates offer an excellent figures for surface enhanced Raman scattering (SERS) sensing, the chemical instability issues of silver...     

Surface Enhanced Raman Spectroscopy Detection of Biomolecules Using EBL Fabricated Nanostructured Substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.     

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.     

Functionalization of nanostructured gold substrates with chiral chromophores for SERS applications: The case of 5‐Aza[5]helicene

Nanostructured gold thin films can be fabricated by controlled pulsed laser deposition to get efficient sensors, with uniform morphology and optimized plasmon resonance, to be employed as plasmonic substrates in surface enhanced Raman scattering spectroscopy. By attaching 5‐aza[5]helicen‐6‐yl‐6‐hexanethiol to such gold nanostructures, used in a previous work for label‐free drug sensing with biomedical purposes, we successfully prepared functionalized substrates with remarkable surface enhanced Raman scattering activity. The long‐term motivation is to develop probes for drug detection at low concentrations, where sensitivity to specific chiral targets is required.     

Cover Picture: J. Biophoton. 3/2009

Graphium weiskei butterfly wings and scanning electron microscope (SEM) micrograph of their detailed nanostructure. The conical cuticular nanostructures found on the metalicized surface of the G. weiskei butterfly display ideal properties as substrates for avidin/biotin assaying using SERS (12 × 10 μm) (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct Electrodeposition of Hollowed Ag Nanostructures on ITO Glass for Reproducible SERS Application

Hollowed Ag nanostructures are, for the first time, electrodeposited on ITO glass without use of surfactant. The hollowed Ag nanostructure was investigated via a collaboration of scanning electron microscopy (SEM), XRD, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), XRD, and UV-vis. Results exhibited that the formation of the hollowed Ag nanostructure can be interpreted as the synergy effect of twin defect and low nucleation driving force. Surface-enhanced Raman scattering (SERS) spectra of rhodamine 6G and adenine molecules adsorbed on the surface of these Ag nanostructures were recorded. The smallest RSD of 1651 cm^?1 Raman bands of rhodamine 6G was 14.7 %, indicating that the hollowed Ag nanostructures can be utilized for reproducible SERS application. Through comparison, it was found the good crystallinity was beneficial for SERS.     

Rational design of thiolated polyenes as trifunctional Raman reporter molecules in surface‐enhanced Raman scattering nanotags for cytokine detection in a lateral flow assay

The characteristic vibrational spectroscopic fingerprint of Raman reporter molecules adsorbed on noble metal nanoparticles is employed for the identification of target proteins by the corresponding surface‐enhanced Raman scattering (SERS) nanotag‐labeled antibodies. Here, we present the modular synthesis of thiolated polyenes with two to five C═C double bonds introduced via stepwise Wittig reactions. The experimental characterization of their electronic and vibrational properties is complemented by density functional theory calculations. Highly SERS‐active nanotags are generated by using the thiolated polyenes as Raman reporter molecules in Au/Au core/satellite supraparticles with multiple hot spots. The cytokines IL‐1β and IFN‐γ are detected in a duplex SERS‐based lateral flow assay on a nitrocellulose test strip by Raman microscopy. The thiolated polyenes are suitable for use in immuno‐SERS applications such as point‐of‐care testing as well as cellular and tissue imaging.     

Raman and surface enhanced Raman spectroscopy of 2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide labeled proteins: bovine serum albumin and cytochrome c

2,2,5,5-Tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide (tempyo) labeled bovine serum albumin and cytochrome c at different pH values were prepared and investigated using Raman-resonance Raman (RR) spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy. The Raman spectra of tempyo labeled proteins in the pH 6.7-11 range were compared to those of the corresponding free species. The SERS spectra were interpreted in terms of the structural changes of the tempyo labeled proteins adsorbed on the silver colloidal surface. The tempyo spin label was found to be inactive in the Raman-RR and SERS spectra of the proteins. The alpha-helix conformation was concluded to be more favorable as the SERS binding site of bovine serum albumin. In the cytochrome c the enhancement of the bands assigned to the porphyrin macrocycle stretching mode allowed the supposition of the N-adsorption onto the colloidal surface.     

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.

     

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.     

SERS观察在Pd OECC薄膜中β-胡萝卜素的基频和高阶拉曼模

利用有极高检测灵敏度的表面增强拉曼散射(SERS)技术,对吸附在银镜表面上的浓度较低的纯化的放氧核心复合物(Pd OECC)薄层进行了频移在250～3 100 cm-1范围内的拉曼光谱测量,除得到β-胡萝卜素分子的基频拉曼振动模外,在高频端还得到了许多弱峰.根据泛音和组合谱带选择定则分析,这些振动模式来自β-胡萝卜素分子的高阶拉曼光谱.还进行了Pd OECC在强光破坏前后的SERS光谱研究.在强光照射下,β-胡萝卜素分子的SERS光谱的散射强度明显降低,且线宽增加,说明强光照射不但改变了β-胡萝卜素的构象,而且也改变了β-胡萝卜素分子所处的微环境.其结果与强光照射前后吸收光谱的变化一致.另外,没有观察到Pd OECC薄层与银镜相互作用的其他新振动峰或Pd OECC中其他振动峰峰型的变化,可见Pd OECC在银镜表面保持原来的状态.这证明SERS技术在光合作用光破坏机理研究中的可行性.     

Surface‐enhanced Raman spectroscopy for on‐site analysis: A review of recent developments

On‐site identification and quantification of chemicals is critical for promoting food safety, human health, homeland security risk assessment, and disease diagnosis. Surface‐enhanced Raman spectroscopy (SERS) has been widely considered as a promising method for on‐site analysis due to the advantages of nondestructive, abundant molecular information, and outstanding sensitivity. However, SERS for on‐site application has been restricted not only by the cost, performance, and portability of portable Raman instruments, but also by the sampling ability and signal enhancing performance of the SERS substrates. In recent years, the performance of SERS for on‐site analysis has been improved through portable Raman instruments, SERS substrates, and other combined technologies. In this review, popular commercial portable Raman spectrometers and the related technologies for on‐site analysis are compared. In addition, different types of SERS substrates for on‐site application are summarized. SERS combined with other technologies, such as electrochemical and microfluidics are also presented. The future perspective of SERS for on‐site analysis is also discussed.     

Feasibility study using surface-enhanced Raman spectroscopy for the quantitative detection of tyrosine and serine phosphorylation

We investigate the feasibility of colloid-based surface enhanced Raman scattering (SERS) as a highly sensitive technique for detecting peptide phosphorylation at serine and tyrosine residues. Using the recently reported drop-coating deposition Raman method we validate our SERS spectra against normal Raman spectra that would otherwise be unobtainable at such low concentrations. Compared with existing techniques for quantifying peptide phosphorylation, such as high-performance liquid chromatography (HPLC), the short scanning and processing time associated with SERS makes it an attractive alternative for near-real-time measurement at sub micro-molar concentrations. Following pre-processing by Savistky-Golay second derivative (SGSD), the degree of phosphorylation of synthetic peptides is determined using multivariate spectral classification, interval partial least squares (iPLS). Furthermore, our results show that the technique is robust to interference from complex proteins and other phosphorylated compounds present at concentrations typically found in a screening assay.     

SERS quantitative detection of trace human chorionic gonadotropin using a label‐free Victoria blue B as probe in the aggregated immunonanogold sol substrate

Nanogold particles (NG) were modified by anti‐rabbit antibody (RAb) against human chorionic gonadotropin to obtain an immunonanogold probe (ING). In pH 7.0 Na₂HPO₄‐citrate buffer solution containing KCl, ING probes formed large aggregates in which Victoria blue B (VBB) molecules were adsorbed on the surface and which exhibited strong surface‐enhanced Raman scattering (SERS) at a peak of 1612 cm^–1. After addition of human chorionic gonadotropin (hCG) an immune reaction with the ING probe occurred to form dispersive ING–hCG complexes with non‐SERS activity that led to a decreased SERS peak at 1612 cm^–1. The decreased SERS intensity was linear to the concentration of hCG over 2.4–73.2 ng/mL. The ING reaction was studied in detail by SERS, scanning electron microscope (SEM), resonance Rayleigh scattering (RRS), surface plasmon resonance (SPR) absorption and laser scattering techniques. SERS quenching was observed and discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure-potential dependence of adsorbed enzymes and amino acids revealed by the surface enhanced Raman effect

Surface enhanced Raman scattering (SERS) of some enzymes (alkaline phosphatase, horseradish peroxidase and lactoperoxidase) and some amino acids (tryptophan, tyrosine and phenylalanine) on silver electrodes has been studied. The spectral band intensities of certain amino acids and amino acid residues were determined by their orientation on the surface and depended on the electrode potential (E).Abbreviations SERS surface enhanced Raman scattering - Trp tryptophan - Tyr tyrosine - Phe phenylalanine - E electrode potential - ORC oxidation-reduction cycle     

Remote-Excitation Time-Dependent Surface Catalysis Reaction Using Plasmonic Waveguide on Sites of Single-Crystalline Crossed Nanowires

The remote-excitation polarization-dependent surface enhanced Raman scattering (SERS) induced by plasmonic waveguide is used to investigate the surface catalysis reaction of 4-nitrobenzenethiol converting to p,p′-dimercaptoazobenzene. The propagating surface plasmon polaritons along single-crystalline nanowires can be coupled by the crossed nanowire as nanoantenna for generating massive electromagnetic field enhancement in the nanogap. The remote-excitation SERS spectra in the nanogap reveal the occurrence of a surface catalysis reaction. The time-dependent remote-excitation SERS spectra further confirmed such surface catalysis reaction. This novel sensitive technology could lead to miniaturized photonics and realize high-resolution microscopy/spectroscopy used in the field of remote catalysis reaction.     

Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 10¹⁴ were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10^?15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.     

Rapid and Sensitive Detection of Rotavirus Molecular Signatures Using Surface Enhanced Raman Spectroscopy

Human enteric virus infections range from gastroenteritis to life threatening diseases such as myocarditis and aseptic meningitis. Rotavirus is one of the most common enteric agents and mortality associated with infection can be very significant in developing countries. Most enteric viruses produce diseases that are not distinct from other pathogens, and current diagnostics is limited in breadth and sensitivity required to advance virus detection schemes for disease intervention strategies. A spectroscopic assay based on surface enhanced Raman scattering (SERS) has been developed for rapid and sensitive detection of rotavirus. The SERS method relies on the fabrication of silver nanorod array substrates that are extremely SERS-active allowing for direct structural characterization of viruses. SERS spectra for eight rotavirus strains were analyzed to qualitatively identify rotaviruses and to classify each according to G and P genotype and strain with >96% accuracy, and a quantitative model based on partial least squares regression analysis was evaluated. This novel SERS-based virus detection method shows that SERS can be used to identify spectral fingerprints of human rotaviruses, and suggests that this detection method can be used for pathogen detection central to human health care.     

Surface‐enhanced Raman scattering‐active photonic crystal fiber probe: Towards next generation liquid biopsy sensor with ultra high sensitivity

The tremendous enhancement factors that surface‐enhanced Raman scattering (SERS) possesses coupled with the flexibility of photonic crystal fibers (PCFs) pave the way to a new generation of ultrasensitive biosensors. Thanks to the unique structure of PCFs, which allows direct incorporation of an analyte into the axially aligned air channels, interaction between the analyte and excitation light could be increased many folds leading to flexible, reliable and sensitive probes that can be used in preclinical or clinical biosensing. SERS‐active PCF probes provide unique opportunity to develop an opto‐fluidic liquid biopsy needle sensor that enables one‐step integrated sample collection and testing for disease diagnosis. Specificity being a key parameter to biosensors, the PCF inside the biopsy needle could be functionalized with targeting moieties to detect specific biomarkers. In this review article, we present some of the most promising recent biosensors based on PCFs including hollow‐core PCFs, suspended‐core PCFs and side‐channel PCFs. We provide a wide range of applications of such platform using Raman spectroscopy, label free SERS or labeled SERS detection and analyze some of the main challenges to be addressed for translating it to a clinically viable next generation sensitive biopsy needle sensing probe.