Surface-enhanced Raman Scattering Of Rhodamine 6G Research Articles

Single sea urchin-MoO3 nanostructure for surface enhanced Raman spectroscopy of dyes.

Enhancing the surface-enhanced Raman scattering (SERS) activity of semiconductor metal oxide nanostructures by controlling the morphology and oxygen vacancies towards trace detection of organics is of significant interest. In this study, MoO3 with a novel sea urchin morphology is synthesized employing chemical bath deposition and consists of hundreds of ∼15 μm long spikes originating from the core forming 20–40 micron globular structures. The spikes taper to form 20 nm sharp tips. SERS of rhodamine 6G (R6G) over MoO3 sea urchins has been investigated and compared to that of 1D h-MoO3 nanorod arrays. The SERS activity is morphology dependent and the sea urchin-like morphology exhibits higher SERS activity with an enhancement factor (EF) of the order 105 and a detection limit of 100 nM, while for h-MoO3 nanorods, the corresponding values are 103 and 1 μM, respectively. X-ray photoelectron spectroscopy reveals a high concentration of Mo+5 states in sea urchins indicating lattice oxygen vacancies. The observed EF is quite high for a metal oxide substrate and is attributed to the enhanced charge transfer between analyte molecules and the substrate promoted by the oxygen vacancies along with surface defects and hydroxyl groups on MoO3 sea urchins providing more active sites for the adsorption of probe molecules. The role of oxygen vacancies is confirmed by the lower EF value exhibited by the stoichiometric 1D h-MoO3. Raman mapping of a single sea urchin is achieved with good R6G intensity and indicates that the tips of spiky features are involved in SERS enhancement. The reusability of substrates is shown for repeated cycles of R6G adsorption by UV irradiation exploiting the photocatalytic activity of MoO3 nanostructures.

Silver overlayer-modified surface-enhanced Raman scattering-active gold substrates for potential applications in trace detection of biochemical species

Because Ag and Au nanoparticles (NPs) possess well-defined localized surface plasmon resonance (LSPR) they are popularly employed in the studies of surface-enhanced Raman scattering (SERS). As shown in the literature and in our previous studies, the advantage of SERS-active Ag NPs is their higher SERS enhancement over Au NPs. On the other hand, the disadvantage of SERS-active Ag NPs compared to Au NPs is their serious decay of SERS enhancement in ambient laboratory air. In this work, we develop a new strategy for preparing highly SERS-active Ag NPs deposited on a roughened Au substrate. This strategy is derived from the modification of electrochemical underpotential deposition (UPD) of metals. The coverage of Ag NPs on the roughened Au substrate can be as high as 0.95. Experimental results indicate that the SERS of Rhodamine 6G (R6G) observed on this developed substrate exhibits a higher intensity by ca. 50-fold of magnitude, as compared with that of R6G observed on the substrate without the deposition of Ag NPs. The limit of detection (LOD) for R6G measured on this substrate is markedly reduced to 2×10−15M. Moreover, aging of SERS effect observed on this developed substrate is significantly depressed, as compared with that observed on a generally prepared SERS-active Ag substrate. These aging tests were performed in an atmosphere of 50% relative humidity (RH) and 20% (v/v) O2 at 30°C for 60 day. Also, the developed SERS-active substrate enables it practically applicable in the trace detection of monosodium urate (MSU)-containing solution in gouty arthritis without a further purification process.

Highly effective surface-enhanced Raman scattering-active gold substrates prepared by using electrochemical methods in the presence of hexadecyltrimethylammonium bromide

As shown in the literature, Au nanoparticles (NPs) were popularly used in the fields of catalyst and surface-enhanced Raman scattering (SERS). Meanwhile, cationic surfactants of hexadecyltrimethylammonium bromide (CTAB) were generally employed in syntheses of Au nanorods (NRs). In this work, CTAB is used to prepare highly effectively SERS-active Au substrates via electrochemical oxidation-reduction cycles (ORCs) for the first time. Based on the effectively SERS-active Au substrate prepared under assistance of CTAB, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by more than one order of magnitude, as compared with that of R6G adsorbed on a SERS-active Au substrate without the assistance of CTAB in preparation. Experimental results indicate that the quantities of adsorption sites for the developed SERS-active Au substrates are large enough to accommodate considerable ranges of analyte concentrations. The aging of SERS enhancement capability can be markedly depressed on this substrate. Moreover, its potential application in the trace detection of monosodium urate (MSU)-containing solution in gouty arthritis can be promised using this SERS-active Au substrate with CTAB.

Surface-Enhanced Raman Scattering-Active Au/SiO2 Nanocomposites Prepared Using Sonoelectrochemical Pulse Deposition Methods

For improving signals, reproducibility, and stabilities of surface-enhanced Raman scattering (SERS), numerous technologies have recently been reported in the literature. However, the fabrication processes are usually complicated. It is well-known that nanoparticles (NPs) of Au and SiO(2) are SERS active and inactive materials, respectively. In this work, a simple synthesis route based on sonoelectrochemical pulse deposition (SEPD) methods has been developed to synthesize effectively SERS-active Au/SiO(2) nanocomposites (NCs) with an enhancement factor of 5.4 × 10(8). Experimental results indicate that pH value of solution and addition of SiO(2) NPs before and after oxidation-reduction cycles (ORCs) can significantly influence the corresponding SERS activities. Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on the developed Au/SiO(2) NCs exhibits a higher intensity by more than 1 order of magnitude, as compared with that of R6G adsorbed on Au NPs synthesized using the same method. Moreover, this improved SERS activity is successfully verified from the mechanisms of electromagnetic (EM) and chemical (CHEM) enhancements.

Surface-enhanced Raman scattering-active gold nanoparticles modified with a monolayer of silver film

As shown in the literature, electrochemical underpotential deposition (UPD) offers the ability to deposit up to a monolayer of one metal onto a more noble metal with a flat surface. In this work, we develop an electrochemical pathway to prepare more surface-enhanced Raman scattering (SERS)-active substrates with Ag UPD-modified Au nanoparticles (NPs) by using sonoelectrochemical deposition-dissolution cycles (SEDDCs). Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on these Ag UPD-modified Au NPs exhibits a higher intensity by ca. 12-fold magnitude, as compared with that of R6G adsorbed on unmodified Au NPs. The prepared SERS-active substrate demonstrates a large Raman scattering enhancement for R6G with a detection limit of 2 × 10(-14) M and an enhancement factor of 5.0 × 10(8). Also, the strategy proposed in this work to improve the SERS effects by using UPD Ag based on SEDDCs has an effect on the smaller probe molecules of 2,2'-bipyridine (BPy).

Improved performance of surface‐enhanced Raman scattering on silver substrates prepared in nitric acid solutions

In this work, we propose a new electrochemical method to prepare surface‐enhanced Raman scattering (SERS)‐active silver substrates in nitric acid solutions. Experimental results indicate that the SERS intensity of adsorbed Rhodamine 6G (R6G) can be significantly increased, as compared with that of R6G adsorbed on a SERS‐active Ag substrate prepared by an electrochemical method in a chloride‐containing solution, which was generally employed in the literature. Moreover, the SERS of R6G on the newly developed substrate (prepared in a nitric acid solution) still performs well at a high temperature of 250 °C. However, the enhancement capability of the SERS‐active substrate prepared in a chloride‐containing solution is seriously destroyed at temperatures higher than 150 °C. Further investigations indicate that the oxidation states of roughened Ag substrates prepared in nitric acid solutions under different experiment conditions have less influence on the corresponding SERS performances. Instead, different surface morphologies of roughened Ag substrates and different contents of nitrogen‐containing dopping ions on the roughened Ag substrates demonstrate significant effects on the corresponding SERS performances. Copyright © 2011 John Wiley & Sons, Ltd.

SERS activity of Au nanoparticles coated on an array of carbon nanotube nested into silicon nanoporous pillar

A novel composite structure, Au nanoparticles coated on a nest-shaped array of carbon nanotube nested into a silicon nanoporous pillar array (Au/NACNT/Si-NPA), was fabricated for surface-enhanced Raman scattering (SERS). The morphology of the Au/NACNT/Si-NPA composite structure was characterized with the aid of scanning electron microscopy, X-ray diffraction instrumentation and Transmission electron microscopy. Compared with SERS of rhodamine 6G (R6G) adsorbed on SERS-active Au substrate reported, the SERS signals of R6G adsorbed on these gold nanoparticles were obviously improved. This was attributed to the enlarged specific surface area for adsorption of target molecules brought by the nest-shaped CNTs structure.

Surface-enhanced Raman scattering-active silver substrates electrochemically prepared in solutions containing bielectrolytes

In the electrochemical oxidation–reduction cycles (ORC) treatment for preparing surface-enhanced Raman scattering (SERS)-active substrates, chloride electrolyte was generally selected because this facilitates the metal dissolution-deposition process that is known to produce SERS-active roughened surfaces. In this work, SERS-active Ag substrates were electrochemically prepared in HCl solutions containing supplemental electrolytes of HNO3. Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on this developed Ag substrate exhibits a higher intensity by 15-fold of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate prepared in HCl solution. Moreover, limit of detection for probe molecules of R6G can be significantly reduced to 2 × 10−15 M. Also, the significant improvements in thermal stability and anti-aging of SERS-active Ag substrates proposed in this work are observed.

Improved performances on surface‐enhanced Raman scattering based on electrochemically roughened gold substrates modified with SiO2 nanoparticles

AbstractIn this work, we use electrochemical oxidation–reduction cycles (ORC) methods to prepare surface‐enhanced Raman scattering (SERS)‐active gold substrates modified with SiO2 nanoparticles to improve the corresponding SERS performances. Based on the modified substrates, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by 3‐fold of magnitude, as compared with that of R6G adsorbed on a SERS‐active Au substrate without the modification of SiO2 nanoparticles. Moreover, the SERS enhancement capabilities of the modified and the unmodified Au substrates are seriously destroyed at temperatures higher than 250 and 200 °C, respectively. These results indicate that the modification of SiO2 nanoparticles can improve the thermal stability of SERS‐active substrates. The aging in SERS intensity is also depressed on this modified Au substrate due to the contribution of SiO2 nanoparticles to SERS effects. Copyright © 2009 John Wiley & Sons, Ltd.

Interesting substrate-temperature dependence on surface-enhanced Raman scattering

We report here an interesting phenomenon that surface-enhanced Raman scattering (SERS) intensity can be significantly improved on electrochemically roughened silver substrates at slightly elevated temperatures. Experimental results indicate that the SERS enhancement capabilities are gradually raised from 25 °C to a maximum at 50 °C and monotonically decreased from 50 to 60 °C. The SERS of Rhodamine 6G (R6G) adsorbed on the SERS-active substrate at 50 °C exhibits a higher intensity by 7-fold of magnitude, as compared with that of R6G adsorbed on the SERS-active substrate at 25 °C. More interestingly, this phenomenon is reversible. The SERS intensity of R6G was also decreased to its original level when the temperature of the elevated substrate was reduced from 50 to 25 °C. These interesting phenomena are valid for all different target molecules generally used in SERS studies. Further experiments reveal that the increase in SERS enhancement capability of SERS-active Ag substrates at slightly elevated temperatures may mainly comes from the corresponding increase of the chemical (CHEM) enhancements.

Effects of substrate temperatures on improved surface-enhanced Raman scattering

In this work, electrochemical methods were used to prepare surface-enhanced Raman scattering (SERS)-active gold substrates to investigate the effect of substrate temperatures on improved SERS performances. The results indicate that the SERS enhancement capabilities are gradually raised from 25 °C to a maximum at 40 °C and monotonically decreased from 40 to 100 °C. The SERS of rhodamine 6G (R6G) adsorbed on the SERS-active substrate at 40 °C exhibits a higher intensity by 4-fold of magnitude, as compared with that of R6G adsorbed on the SERS-active substrate at 25 °C. Also, SERS of polypyrrole (PPy) deposited on the roughened Au substrate treated at 35 °C exhibits the highest intensity by 3-fold of magnitude, as compared with that of PPy deposited on the same roughened Au substrate at room temperature.

Enhancements in intensity and thermal stability of Raman spectra based on roughened gold substrates modified by underpotential deposition of silver

AbstractIn this study, electrochemically roughened gold is modified with underpotential deposition (UPD) silver to investigate the effects on enhancements in the intensity and the thermal stability of surface‐enhanced Raman scattering (SERS). The SERS of Rhodamine 6G (R6G) adsorbed on the UPD Ag‐modified Au substrate exhibits a higher intensity by six‐fold of magnitude, as compared with that of R6G adsorbedon the unmodified Au substrate. Moreover, the SERS enhancement capabilities of UPD Ag‐modified Au and unmodified Au substrates are seriously depressed at temperatures higher than 200 and 150 °C, respectively. It indicates that the modification of UPD Ag can significantly depress the thermal destruction of SERS‐active substrates. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of TiO2 Nanoparticles on the Improved Performances on Electrochemically Prepared Surface-Enhanced Raman Scattering-Active Silver Substrates

In this work, we use electrochemical oxidation−reduction cycles (ORC) methods to prepare surface-enhanced Raman scattering (SERS)-active silver substrates modified with TiO2 nanoparticles to improve the corresponding SERS performances. On the basis of the modified substrates, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by 4-fold of magnitude, as compared with that of R6G adsorbed on a SERS-active Ag substrate without the modification of TiO2 nanoparticles. Moreover, the SERS enhancement capabilities of the modified and the unmodified Ag substrates are seriously destroyed at temperatures higher than 200 and 125 °C, respectively. These results indicate that the modification of TiO2 nanoparticles can improve the thermal stability of SERS-active substrates. More interestingly, the SERS intensity of R6G was significantly increased by 9-fold of magnitude, as the temperature of the modified Ag substrate was raised from 25 to 125 °C. The aging in SERS intensity is also depressed on this modified Ag...

Novel surface-enhanced Raman scattering-active silver substrates containing visible light-responsible Tio2 nanoparticles

We report here the first electrochemically prepared surface-enhanced Raman scattering (SERS)-active silver substrates containing visible light-responsible TiO2 nanoparticles. The SERS-active Ag substrates with TiO2 nanoparticles were prepared by roughening the substrates using electrochemical oxidation–reduction cycles (ORC) in 0.1 M HCl aqueous solutions containing 1 mM visible light-responsible TiO2 nanoparticles. Based on these prepared substrates, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate without TiO2 nanoparticles. Moreover, the practical limit of detection (LOD) of R6G can be reduced by five orders of magnitude from 2 × 10−10 to 2 × 10−15 M owning to the additional contribution of TiO2 nanoparticles to the whole SERS effects.

Improved surface-enhanced Raman scattering on electrochemically roughened silver substrates prepared in bielectrolyte solutions

In this work, the effect of supplemental LiClO 4 electrolytes in KCl solutions used in roughening silver substrates by electrochemical triangular-wave oxidation–reduction cycles (ORC) on surface-enhanced Raman scattering (SERS) was first investigated. To prepare SERS-active substrates by ORC procedures, electrolytes of KCl were generally employed. In contrast, LiClO 4 ones were unsuitable for producing SERS-active substrates. Encouragingly, SERS of Rhodamine 6G (R6G) adsorbed on the roughened Ag substrate prepared in an aqueous solution containing KCl and LiClO 4 electrolytes exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate prepared in a solution only containing KCl. Further investigations indicate that the oxidation state of Cl on the roughened Ag substrate demonstrates decided effects on this improved SERS.

Strategy for obtaining improved surface-enhanced Raman scattering by combining electrochemical and plasmas technologies

In this work, surface-enhanced Raman scattering (SERS)-active gold substrates were first developed by combining the technologies of oxidation–reduction cycles (ORCs) and plasmas treatments in roughening metal substrates. First, a gold substrate was treated by argon plasmas. Then the treated gold substrate was further roughened by triangular-wave ORCs in an aqueous solution containing 0.1 M HCl. Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on this roughened gold substrate modified by argon plasmas pretreatment exhibits a higher intensity by 10-fold of magnitude and a better resolution, as compared with the SERS of R6G adsorbed on an unmodified roughened gold substrate. Meanwhile, the probing concentration of R6G adsorbed on the modified substrate can be reduced by one order. It was also found that the pretreatment of argon plasmas demonstrates a positive effect on the (2 2 0) face of Au partly changing into the (1 1 1) face with the lowest surface energy after the ORCs roughening, which is contributive to the improved SERS observed.