Room-temperature sensor based on surface-enhanced Raman spectroscopy.

As reported in the literature, several factors, such as scattering cross sections, polarisability and wavelength suitability, contribute to increased SERS enhancement. In general, the advantage of surface-enhanced Raman scattering (SERS)-active Ag nanoparticles (NPs) is their higher SERS enhancement over Au NPs because the molar extinction coefficient of the Ag NPs is the highest of its kind among metals. Nevertheless, the corresponding SERS-active hot spots on Au are of inherently greater stability than on Ag. In this work, innovative temperature sensors based on SERS-active Au and Ag substrates prepared by sonoelectrochemical deposition-dissolution cycles (SEDDCs) are first reported. The SERS intensity of the model probe molecules of Rhodamine 6G (R6G) adsorbed on a SERS-active Ag substrate is monotonically increased from 25 to 50 °C. Moreover, this temperature-dependent intensity is linear with a slope of ca. 430 cps per °C between 25 to 45 °C. In addition, the reversibility and reusability of the developed temperature sensors are evaluated after the R6G-adsorbed sensors are alternately exposed to the temperatures of 25 and 45 °C in a sealed chamber. After every five cycles, the SERS spectra of treated substrates were recorded and compared with those of the as-prepared substrates. Experimental results indicate that SERS enhancement capability is mostly reversible based on 90% intensity of the Raman signal being maintained for the SERS-active Au substrate after 25 cycles (only 15 cycles for the Ag substrate).

Active and stable liquid water innovatively prepared using resonantly illuminated gold nanoparticles.

The properties of confined liquid water, or liquid water in contact with hydrophobic surfaces, are significantly different from those of bulk liquid water. However, all of water's commonly described properties are related to inert "bulk liquid water" which comprises a tetrahedral hydrogen-bonded network. In this work, we report an innovative and facile method for preparing small water clusters (SWCs) with reduced affinity hydrogen bonds by letting bulk water flow through supported Au nanoparticles (NPs) under resonant illumination to give NP-treated (AuNT) water at constant temperature. Utilizing localized surface plasmon resonance on illuminated Au NPs, the strong hydrogen bonds of bulk water can be disordered when water is located at the illuminated Au/water interface. The prepared SWCs are free of Au NPs. The energy efficiency for creating SWCs is ∼17%. The resulting stable AuNT water exhibits distinct properties at room temperature, which are significantly different from the properties of untreated bulk water, examples being their ability to scavenge free hydroxyl and 2,2-diphenyl-1-picrylhydrazyl radicals and to effectively reduce NO release from lipopolysaccharide-induced inflammatory cells.

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).

Surface-enhanced Raman scattering-active silver nanostructures with two domains.

Generally, a controllable and reproduced surface roughness for surface-enhanced Raman scattering (SERS) studies can be generated through control of the electrochemical oxidation-reduction cycles (ORC) procedure. In this work, we propose a new sonoelectrochemical approach to prepare SERS-active substrates with two domain-Ag nanostructures. The method is based on a strategy of deposition-dissolution cycles (DDCs) by using a cathodic overpotential and an anodic overpotential from open circuit potential (OCP) in turn under sonication. The prepared SERS-active substrate demonstrates large Raman scattering enhancement for adsorbed Rhodamine 6G (R6G) with an enhancement factor of 2.3×10(8) and a limit of detection of 2×10(-13)M. The improved SERS performances can be successfully explained from the viewpoints of electromagnetic (EM) and chemical (CHEM) enhancements.

Electrochemically prepared surface-enhanced Raman scattering-active silver substrates with improved stabilities.

In this work, SiO2 nanoparticles-modified surface-enhanced Raman scattering (SERS)-active silver substrates were prepared by electrochemical oxidation-reduction cycles (ORC) methods in 0.1 N HCl aqueous solutions containing 1 mM SiO2 nanoparticles to improve their thermal stabilities and anti-aging abilities in SERS performances. Then these SERS-active substrates were further modified with different contents of SiO2 nanoparticles to improve their corresponding SERS performances. Experimental results indicate that the operation temperature can be significantly raised from 125 to 175°C based on this modified SERS-active Ag substrate. Also, the aging in SERS intensity is also depressed on this modified Ag substrate due to the contribution of SiO2 nanoparticles. Moreover, the SERS enhancement capability on this modified Ag substrate is gradually raised from 25°C to a maximum at 55°C and monotonically decreased from 55 to 60°C. This is a 10°C delay as compared with the similar phenomenon observed on the unmodified Ag substrate.

Simple strategy to improve surface-enhanced Raman scattering based on electrochemically prepared roughened silver substrates.

We develop an easy and effective pathway to improve surface-enhanced Raman scattering (SERS) effects of probe molecules of Rhodamine 6G (R6G) adsorbed on electrochemically prepared roughened Ag substrates. In general SERS studies, SERS-active metal substrates are first prepared. Then probe molecules are adsorbed on them to evaluate the relative SERS effects. In this study, we employ electrochemical oxidation-reduction cycle (ORC) treatments in 0.1 M KCl solutions containing probe molecules of 2 x 10(-5) M R6G to prepare R6G-adsorbed SERS-active Ag substrates for one step. Encouragingly, based on this strategy, the SERS intensity of adsorbed R6G can be increased by 1 order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate beforehand, which was generally shown in the literature. Moreover, this improved SERS effect based on this strategy is also effective for 2 x 10(-9) M probe molecules, which is at a level of single molecule detection based on Ag colloids. It is also effective for probe molecules of ClO(4)(-) with low Raman cross section and for other electrochemically prepared SERS-active substrates of Au. Further analyses indicate that the increase in SERS activity in this new method is most likely due to the incorporation of more chloride ions into the substrate.

Temperature effect of electrochemically roughened gold substrates on polymerization electrocatalysis of polypyrrole.

In this work, electrochemical methods were used to prepare complexes with Au and Cl species on bulk Au substrates. Then the electrochemically roughened Au substrates were further heat-treated at different temperatures. The effect of temperatures used in heat treatments between 25 and 100 degrees C on electrocatalytical polymerization of polypyrrole (PPy) formed on the prepared gold substrates was first investigated. The result indicates that the optimally electrocatalytical capability of the heat-treated Au substrate for PPy polymerization is at 75 degrees C. Moreover, the autopolymerized PPy on the roughened Au substrate treated at 75 degrees C demonstrates the highest oxidation level and oxidation degree of 0.32 and 0.50, respectively. Primary results indicate that complexes with positively charged Au act as oxidants, and perchlorate and chloride ions act as dopants for the oxidation-polymerization of PPy.

Scaling characteristics in ozone concentration time series (OCTS).

One-year series of hourly average ozone observations, which were obtained from urban and national park air monitoring stations at Taipei (Taiwan), were analyzed by means of descriptive statistics and fractal methods to examine the scaling structures of ozone concentrations. It was found that all ozone measurements exhibited the characteristic right-skewed frequency distribution, cyclic pattern, and long-term memory. A mono-fractal analysis was performed by transferring the ozone concentration time series (OCTS) into a useful compact form, namely, the box-dimension (D(B))-threshold (T(h)) and critical scale (C(S))-threshold (T(h)) plots. Scale invariance was found in these time series and the box dimension was shown to be a decreasing function of the threshold ozone level, implying the existence of multifractal characteristics. To test this hypothesis, the OCTS were transferred into the multifractal spectra, namely, the tau(q)-q plots. The analysis confirmed the existence of multifractal characteristics in the investigated OCTS. A simple two-scale Cantor set with unequal scales and weights was then used to fit the calculated tau(q)-q plots. This model fitted remarkably well the entire spectrum of scaling exponents for the examined OCTS. Because the existence of chaos behavior in OCTS has been reported in the literature, the possibility of a chaotic multifractal approach for OCTS characterization was discussed.

Improved surface-enhanced Raman scattering on optimum electrochemically roughened silver substrates.

In this work, the effects of preparation conditions used in roughening silver substrates by electrochemical triangular-wave oxidation-reduction cycles (ORC) on surface-enhanced Raman scattering (SERS) were first investigated. The optimum roughening conditions for obtaining strongest SERS of Rhodamine 6G (R6G) are as follows. Ag electrodes were cycled in deoxygenated aqueous solutions containing 0.1 M NaCl from -0.3 to +0.2 V versus Ag/AgCl at 25 mV s(-1) for five scans. The SERS of R6G adsorbed on this optimum procedure-prepared roughened Ag substrate exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a normally roughened Ag substrate.