High Surface Enhanced Raman Spectroscopy Research Articles

Novel core–shell structured Paclitaxel-loaded PLGA@Ag–Au nanoparticles

Novel core–shell structured anti-cancer drug-loaded poly(lactide-co-glycolide) @Ag–Au nanoparticles (NPs) for medical applications were synthesized and characterized. Monodispersed, Paclitaxel (PTX)-loaded PLGA NPs, which were fabricated using a stabilizer-free method, served as the device core and facilitated Ag NP nucleation on their surface. A shell of Ag NPs was formed in situ on PLGA NPs through the controlled reduction of AgNO3 by polyvinylpyrrolidone (PVP). The intermediate PLGA@Ag NPs were used to grow Ag–Au nanoshells on PLGA core in a replacement reaction. The bimetallic Ag–Au nanoshell could serve as an optimal metal enhancer for surface enhanced Raman spectroscopy (SERS). SERS experiments using 4-MBA as the Raman reporter showed that the PTX-loaded PLGA@Ag–Au hybrid NPs provided enormously amplified SERS signals, which would make them as highly desirable SERS optical tags in biomedical imaging. With a combination of functions of high SERS activity, controlled anti-cancer drug release and hyperthermal effect, the PTX-loaded PLGA@Ag–Au NPs have the potential as new theranostics for effective cancer detection and treatment.

Three Steps of Hierarchical Self Assembly Toward a Stable and Efficient Surface Enhanced Raman Spectroscopy Platform

We report an innovative application of a true “bottom-up” approach for preparation of functional material. Three consecutive self-assembly steps were utilized for formation of a complex surface enhanced Raman spectroscopy (SERS) platform. First the Langmuir–Blodgett technique was used to deposit gold nanoparticles on a solid substrate. Thus prepared surfaces were afterward used as substrates in the chemical vapor deposition process of gallium nitride (GaN) nanowire growth. On such scaffolding, a third step of material fabrication was performed. Gold microflowers (Au MFs) deposited from solution preferably appeared at the top of the GaN nanowires and not in the cavities in between. The obtained morphology of the final material was controlled at each step of the preparation process to tailor its properties for desired purposes. Prepared surfaces were tested as SERS platforms. The enhancement factor was around 107 in case of p-mercaptobenzoic acid (p-MBA). The platforms were also suitable for biological and biomedical applications. We demonstrated the label free detection of DNA. The substrates gave reproducible SERS spectra both across a single platform and between different platforms. The average spectral correlation coefficients (Γ) was 0.87. Moreover, the obtained material proved to be very stable. The presented complex structure demonstrated therefore had the advantages of the two surface functionalization concepts it comprised: (1) GaN nanowire growth and (2) Au MF deposition, eliminating their major drawbacks. Presented material combined high SERS enhancement factor of Au MFs deposited on a flat surface and good durability of microflowers deposited on a surface completely covered with nanowires, which were almost SERS inactive. The final product provided truly exceptional stability and repeatability of SERS results, maintaining an enhancement factor comparable to the best commercially available platforms.

Au-coated ZnO nanostructures for surface enhanced Raman spectroscopy applications**Reported at the XIX International Conference on Advanced Laser Technologies (ALT'11), Bulgaria, Golden Sands, September 2011.

Thin ZnO nanostructured films were produced by pulsed laser deposition (PLD) for surface enhanced Raman spectroscopy (SERS) studies. The experimental conditions used for preparation of the samples were chosen to obtain different types of ZnO nanostructures. The Raman spectra of rhodamine 6G (R6G) were measured at an excitation wavelength of 785 nm after coating the ZnO nanostructures with a thin Au layer. The influence of the surface morphology on the Raman signal obtained from the samples wasinvestigated. High SERS signal enhancement was observed from all Au-coated ZnO nanostructures.

Large-Area Organization of pNIPAM-Coated Nanostars as SERS Platforms for Polycyclic Aromatic Hydrocarbons Sensing in Gas Phase

Here, a new surface enhanced Raman spectroscopy (SERS) platform suitable for gas phase sensing based on the extended organization of poly-N-isopropylacrylamide (pNIPAM)-coated nanostars over large areas is presented. This system yields high and homogeneous SERS intensities, and simultaneously traps organic chemical agents as pollutants from the gas phase. pNIPAM-coated gold nanostars were organized into parallel linear arrays. The optical properties of the fabricated substrates are investigated, and applicability for advanced sensing is demonstrated through the detection in the gas phase of pyrene traces, a well-known polyaromatic hydrocarbon.

Morphology control of 1D noble metal nano/heterostructures towards multi-functionality

We synthesize Pt, Pd, Au and layered multimaterial nanotubes via electrodeposition in anodic aluminium oxide (AAO) templates. We show that time controlled growth at constant electrolyte concentration allows the morphology and chemistry of the nanostructure to be controlled to a high degree. In particular the wall thickness of the nanotubes can be tuned from thin wall nanotubes to nanorods. The applications targeted are electrocatalysis, plasmon resonance and molecular detection via surface enhanced Raman spectroscopy (SERS). The electro-oxidation of methanol on Pt and that of formic acid on Pd are investigated and compared with state of the art Pt/C and Pd/C catalysts and some of the recent similar work from the literature. Nanotubes of both metals (Pt, Pd) show very high electrochemical surface area (ECSA) and enhanced electrocatalytic activity. Our electrocatalysis results show great promise towards direct liquid fuel cells. In terms of molecular detection using SERS we show that the SERS activity of Au-nanostructures is strongly dependent on morphology with very high SERS enhancements being related to partly filled Au-nanotubes.

Single base extension reaction-based surface enhanced Raman spectroscopy for DNA methylation assay

DNA methylation is a key diagnostic maker for genetic disease, cancer progression and pharmcogenomics. So far various techniques have been developed for DNA methylation assay, but most of them are laborious and time-consuming. Here we develop a simple and highly sensitive DNA methylation assay based on single base extension reaction and surface enhanced Raman spectroscopy (SERS). In the presence of methylated DNA, gold nanoparticle-modified capture probe can couple with a cyanine 5-deoxyribonucleoside triphosphate (cy5-dGTP) through single base extension reaction, and generates a high SERS signal after further addition of gold nanoparticles to increase the local electromagnetic field. While in the presence of unmethylated DNA, gold nanoparticle-modified capture probe cannot couple with cy5-dGTP due to the presence of a mismatch base, and no SERS signal is observed. This single base extension reaction-based SERS can determine methylated DNA with a detection limit of 3pM, and can even distinguish as low as 1% methylation level in tumor suppressor gene CDKN2/p16/MTS1 (p16) from the mixtures. Notably, the sensitivity of this assay has improved by 5 orders of magnitude as compared to reported gold nanoparticle-based colorimetric assay, and by 2 orders of magnitude as compared to microarray-based methylation-sensitive single nucleotide primer extension assay (Ms-SNuPE). This method might be further applied to detect the methylation status in tumor-linked genes for cancer diagnosis.

A route to apply Ag nanoparticle array integrated with microfluidic for surface enhanced Raman scattering

Surface enhanced Raman spectroscopy (SERS) with enormous enhancements has shown great potential in single-molecule detection, however, the fabrication of large-scale and controllable substrates with high SERS activity is a major limitation. To achieve this goal, this paper provides method to fabricate wafer level SERS substrate with tunable nanoparticle sizes and interparticle gaps. The nanoparticle size, density, and shape are found to be dependent on the thickness of Ag film and the condition of annealing. Ag nanoparticles on the silicon substrate were packaged with polydimethylsiloxane (PDMS) microchannel before testing. The results of detections of Rhodamine 6G SERS spectra show that the fabrication protocol of such a SERS substrate is low-cost, easy-fabrication and inexpensive. Therefore, this substrate with Ag nanoparticle array may anticipate a wide range of applications in SERS-based sensors.

Sensitive carbohydrate detection using surface enhanced Raman tagging.

Glycomic analysis is an increasingly important field in biological and biomedical research as glycosylation is one of the most important protein post-translational modifications. We have developed a new technique to detect carbohydrates using surface enhanced Raman spectroscopy (SERS) by designing and applying a Rhodamine B derivative as the SERS tag. Using a reductive amination reaction, the Rhodamine-based tag (RT) was successfully conjugated to three model carbohydrates (glucose, lactose, and glucuronic acid). SERS detection limits obtained with a 633 nm HeNe laser were ∼1 nM in concentration for all the RT-carbohydrate conjugates and ∼10 fmol in total sample consumption. The dynamic range of the SERS method is about 4 orders of magnitude, spanning from 1 nM to 5 μM. Ratiometric SERS quantification using isotope-substituted SERS internal references allows comparative quantifications of carbohydrates labeled with RT and deuterium/hydrogen substituted RT tags, respectively. In addition to enhancing the SERS detection of the tagged carbohydrates, the Rhodamine tagging facilitates fluorescence and mass spectrometric detection of carbohydrates. Current fluorescence sensitivity of RT-carbohydrates is ∼3 nM in concentration while the mass spectrometry (MS) sensitivity is about 1 fmol, achieved with a linear ion trap electrospray ionization (ESI)-MS instrument. Potential applications that take advantage of the high SERS, fluorescence, and MS sensitivity of this SERS tagging strategy are discussed for practical glycomic analysis where carbohydrates may be quantified with a fluorescence and SERS technique and then identified with ESI-MS techniques.

Photonic crystals with SiO2–Ag “post-cap” nanostructure coatings for surface enhanced Raman spectroscopy

We demonstrate that the resonant near fields of a large-area replica molded photonic crystal (PC) slab can efficiently couple light from a laser to SiO2–Ag “post-cap” nanostructures deposited on the PC surface by a glancing angle evaporation technique for achieving high surface enhanced Raman spectroscopy (SERS) enhancement factor. To examine the feasibility of the PC-SERS substrate, the simulated electric field around individual Ag particles and the measured Raman spectrum of trans-1,2-bis(4pyridyl)ethane on the PC-SERS substrate were compared with those from an ordinary glass substrate coated with the same SiO2–Ag nanostructures.

Electrochemical modification of Cu–Zr amorphous alloys for catalysts

This paper presents the authors’ attempts to use some strictly controlled electrochemical processes of dissolution/redeposition of Cu (including disproportionation of Cu + to Cu metal and Cu 2+) to modify its surface, as well as surfaces of Cu base amorphous alloys (AA), to produce active substrates for various phenomena of adsorption and catalytic reactions. New methods of activation of the Cu substrate have been developed for in situ investigations of adsorbates with surface enhanced Raman spectroscopy (SERS). The method consisting in fast dissolution/redeposition produces a clean and large specific surface area substrate, which results in high quality SERS spectra. This method appeared also useful for a modification of the surface activity of partially devitrified Cu–Zr amorphous alloys. Energy dispersive spectrometry (EDS)/X-ray electron microprobe investigations of both AA ribbon surface and its cross-section revealed a peculiar structure of the devitrified material: some multilayer sandwiches of Cu/ZrO 2 were formed locally. Their fractal edges formed certain ‘flowers’ of Cu clusters supported by ZrO 2. The electrochemical pre-treatment was eventually applied after this partial devitrification. The catalytic efficiency of dehydrogenation of 2-propanol at such a pre-treated Cu–Zr substrate increased up to a factor of 2. It has been found that the increase in the SERS activity of an electrochemically pretreated Cu–Zr substrate and the enhancement of its catalytic efficiency are of the same morphological and compositional origin. A tentative mechanism of the surface activation is discussed.

Modification of surface activity of Cu–Zr amorphous alloys and Cu metal by electrochemical methods

This paper summarizes our attempts to use some strictly controlled electrochemical processes of dissolution/redeposition of Cu (including disproportionation of Cu + to Cu metal and Cu 2+ ) to modify Cu surfaces, as well as surfaces of Cu base amorphous alloys (AA), to produce active substrates for various phenomena of adsorption and catalytic reactions. We developed some new methods of activation of the Cu substrate for in situ investigations of adsorbates with SERS (Surface Enhanced Raman Spectroscopy). The first method developed produced an oxidized Cu surface. A distinct spectral shift of the bands characteristic of the adsorbate was observed, due to its interaction with Cu 2 O instead of interacting with metallic Cu. The second method produced a substrate with a clean surface and large specific surface area which resulted in a high quality SERS spectrum exhibiting a 10-fold increase in the signal-to-noise ratio, compared to the results for the surface pretreated by commonly used methods of surface roughening (oxidation–reduction cycling). The third method included an irreversible, diffusion-controlled Cu deposition onto a substrate and resulted in a rather complex, partially oxidized substrate with Cu clusters exhibiting a variety of SERS activities. The second method appeared also useful for the modification of the surface activity of Cu–Zr amorphous alloys. This method was combined with an ageing process of the AA to produce a partial devitrification of the substrate. The electrochemical pretreatment was then applied after this partial devitrification. The catalytic efficiency for dehydrogenation of 2-propanol on such a pretreated Cu–Zr substrate increased by a factor of two. A correlation has been found between the SERS activity of an electrochemically pretreated substrate and its catalytic efficiency. A tentative mechanism of surface activation is discussed.