Why Is Surface-Enhanced Raman Scattering Insensitive to Liquid Water?

Surface-enhanced Raman scattering (SERS) is widely recognized as a remarkably powerful analytical technique that enables trace-level detection of organic molecules on a metal surface in aqueous systems with negligible spectral interference of water. This insensitivity of SERS to liquid water is violated in a restrictive manner under specific electrochemical conditions. However, the origin of such different SERS sensitivities to liquid water remains unclear. Here, we show that hydrogen-bond networks of water play a pivotal role in losing SERS enhancement for liquid water, and SERS detection of water requires local defects in the hydrogen-bond networks, which are formed around hydration shells of solute ions or on a polarized electrode surface. This work gives a new perspective on in situ SERS investigations in aqueous systems, including electrochemical and biological reactions.

Revisit of the plasmon-mediated chemical transformation of para-aminothiophenol.

Fingerprint Raman features of para-aminothiophenol (pATP) in surface-enhanced Raman scattering (SERS) spectra have been widely used to measure plasmon-driven catalytic activities because the appearance of characteristic spectral features is purported to be due to plasmon-induced chemical transformation of pATP to trans-p,p'-dimercaptoazobenzene (trans-DMAB). Here, we present a thorough comparison of SERS spectra for pATP and trans-DMAB in the extended range of frequencies covering group vibrations, skeletal vibrations, and external vibrations under various conditions. Although the fingerprint vibration modes of pATP could be almost mistaken with those of trans-DMAB, the low-frequency vibrations revealed distinct differences between pATP and DMAB. Photo-induced spectral changes of pATP in the fingerprint region were explained well by photo-thermal variation of the Au-S bond configuration, which affects the degree of the metal-to-molecule charge transfer resonance. This finding indicates that a large number of reports in the field of plasmon-mediated photochemistry must be reconsidered.

Engineered Au@CuO Nanoparticles for Wide-Range Quantitation of Sulfur Ions by Surface-Enhanced Raman Spectroscopy.

Efficient detection of sulfide ions (S2-), especially in a wide quantitative range, is of significance but faces challenges. This work strategizes and fabricates Au@CuO nanoparticles for quantitative surface-enhanced Raman spectroscopy (SERS) detection of the S2- ions based on the S2- concentration-dependent ion-solid interactions. We have achieved fast and quantitative S2- detection in a wide range from 5 ppb to 64,000 ppm (saturation concentration of the S2- source). We also demonstrated that the optimal CuO shell thickness for the detection is about 7 nm and that the detection can be further improved by prolonging the soaking duration. Moreover, this detection method has also shown the merits of reusable substrates (especially for low S2- concentrations) and good anti-interference ability to many common anions (Cl-, NO3-, OH-, HCOO-, CO32-, and SO42-). Finally, the high feasibility of this detection in actual water (tap water and pond water) has also been demonstrated. This work provides efficient S2- detection with great potential in practical use and also inspires the design of quantifiable SERS substrates for detecting more small inorganic molecules and ions.

A single spectroscopic probe for in situ analysis of electronic and vibrational information at both sides of electrode/electrolyte interfaces using surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) at electrode/electrolyte interfaces includes inelastic light scattering not only by molecular vibrations in the electrolyte phase but also by conduction electrons in the metal electrode phase. While the former, i.e., vibrational SERS (VSERS), is widely used to obtain chemical information on electrode surfaces, the latter, i.e., electronic SERS (ESERS), is still under discussion as a possible origin of the SERS background. Given that electronic Raman scattering is essentially sensitive to the surface charge density of a metal, we conducted a thorough comparison of electrochemical potential dependence of SERS signals in both acidic and alkaline media. Significant intensity changes in the SERS background were observed close to the respective potentials of zero charge in acidic and alkaline media, supporting the contention that the generation of the SERS background can be explained by the ESERS mechanism. Moreover, the ESERS intensities, as the SERS background, were reversibly varied by anion adsorption/desorption at the electrochemical interfaces in conjunction with VSERS features originated from surface-adsorbate vibrations. The sensitivity to the surface charge was much higher in this method than in the conventional combined method of reflectance and SERS. In situ monitoring of both chemical and electronic structures at electrode/electrolyte interfaces using a single spectroscopic probe can avoid various experimental uncertainties caused by combined application of different spectroscopic methods leading to facilitation of our deeper understanding of electrode processes.

In situ observation of Pt oxides on the low index planes of Pt using surface enhanced Raman spectroscopy.

In situ vibrational spectra of Pt oxides that cannot be measured with IR spectroscopy have been studied on the low index planes of Pt using surface enhanced Raman spectroscopy with bare Au nanoparticles (NPSERS). Two bands appear around 570 and 340 cm-1 at higher potentials in 0.1 M HClO4 saturated with Ar, which are assigned to the stretching vibration of Pt-O(H) and the libration vibration of Pt-O, respectively. NPSERS spectra are measured in O2 saturated solution for the first time. The band intensities of Pt-O(H) and Pt-O in O2 saturated solution are enhanced significantly compared with those in Ar saturated solution. The onset potentials of Pt-O and Pt-O(H) formation are 1.15 V(RHE) on Pt(100) and 1.2 V(RHE) on Pt(111) and Pt(110). The onset potential of Pt-O and Pt-O(H) and band shape differ from the results obtained using shell isolated surface enhanced Raman spectroscopy (SHINERS). The Pt-O and Pt-O(H) band intensities are normalized using COad as an internal standard. The Pt-O(H) band intensity depends on surface structures as Pt(110) < Pt(111) ≪ Pt(100), whereas the Pt-O band gives a different intensity order for Pt(111) and Pt(110) as Pt(111) ≤ Pt(110) ≪ Pt(100) in O2 saturated solution.

Site-Selection in Single-Molecule Junction for Highly Reproducible Molecular Electronics.

Adsorption sites of molecules critically determine the electric/photonic properties and the stability of heterogeneous molecule-metal interfaces. Then, selectivity of adsorption site is essential for development of the fields including organic electronics, catalysis, and biology. However, due to current technical limitations, site-selectivity, i.e., precise determination of the molecular adsorption site, remains a major challenge because of difficulty in precise selection of meaningful one among the sites. We have succeeded the single site-selection at a single-molecule junction by performing newly developed hybrid technique: simultaneous characterization of surface enhanced Raman scattering (SERS) and current-voltage (I-V) measurements. The I-V response of 1,4-benzenedithiol junctions reveals the existence of three metastable states arising from different adsorption sites. Notably, correlated SERS measurements show selectivity toward one of the adsorption sites: "bridge sites". This site-selectivity represents an essential step toward the reliable integration of individual molecules on metallic surfaces. Furthermore, the hybrid spectro-electric technique reveals the dependence of the SERS intensity on the strength of the molecule-metal interaction, showing the interdependence between the optical and electronic properties in single-molecule junctions.

Vibrational Spectroscopic Observation of Atomic-Scale Local Surface Sites Using Site-Selective Signal Enhancement.

Molecule-substrate interactions are sensitively affected by atomic-scale surface structures. Unique activity in heterogeneous catalysts or electrocatalysts is often related with local surface sites with specific structures. We demonstrate that adsorption geometry of a model molecule with an isocyanide anchor is drastically varied among one-fold atop, two-fold bridge, and three-fold hollow configurations with increasing the size of atomic-scale local surface sites of Pd islands on an Au(111) model surface. The vibrational spectroscopic observation of such local information is realized by site-selective and self-assembled formation of hotspots, where Raman scattering intensity is significantly enhanced via excitation of localized surface plasmons.

[Harmonization of TSH Measurements.]

The measured concentration of thyroid stimulating hormone (TSH) differs depending on the reagents used. Harmonization of TSH is crucial because the decision limits are described in current clinical practice guide- lines as absolute values, e.g. 2.5 mIU/L in early pregnancy. In this study, we tried to harmonize the report- ed concentrations of TSH using the all-procedure trimmed mean. TSH was measured in 146 serum samples, with values ranging from 0.01 to 18.8 mIU/L, using 4 immunoassays. The concentration of TSH was highest with E test TOSOH and lowest with LUMIPULSE. The concentrations with each reagent were recalculated with the following formulas: E test TOSOH 0.855x-0.014; ECLusys 0.993x+0.079; ARCHITECT 1.041x- 0.010; and LUMIPULSE 1.096x-0.015. Recalculation eliminated the between-assay discrepancy. These formulas may be used until harmonization of TSH is achieved by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC).

Effects of atomic geometry and electronic structure of platinum surfaces on molecular adsorbates studied by gap-mode SERS.

Surface enhanced Raman scattering (SERS) spectra of organic monolayers were measured on various types of polycrystalline and single crystalline Pt substrates with nanometric or atomic surface features, including heteroepitaxial Pt monolayers, using sphere-plane type nanogap structures. Although atomic geometry and electronic structures of a metal surface significantly influence metal-molecule interactions, such effects are often hindered in conventional SERS measured on a roughened surface because of the spectral information averaging at various adsorption sites. In this study, the use of atomically defined Pt surfaces revealed detailed surface effects; the observed preferential adsorption geometry on each surface was well explained by atomic surface arrangements. The peak shift of the intramolecular vibration in the anchor group was in good agreement with the variation of the d-band center of Pt substrates. Moreover, in electrochemical SERS study the Stark shift of an extramolecular vibrational mode at around 400 cm(-1), which is not accessible in infrared absorption spectroscopy, was monitored on an atomically defined heteroepitaxial Pt monolayer electrode.

[Nutrition Support as Team Medical Care].

Nutrition support is important to prevent complicating disorders such as infections and decubitus and to improve patient outcomes. The nutrition support team (NST), which is usually composed of a physician, nurse, nutritionist, clinical laboratory technician, pharmacist, and office worker, is effective for preventing complications and reducing costs for hospitalized patients. To screen for malnutrition in an early phase, biochemical markers are useful. Transthyretin (TTR) is a serum protein synthesized mainly by the liver. TTR has a short half-life in the bloodstream of 2 days, and is often used as a rapid and sensitive marker of malnutrition. However, TTR also decreases under inflammatory and infectious conditions. We recently established the Kumamoto Index to assess both the inflammatory and nutritional state of patients.

Enhancement of SERS background through charge transfer resonances on single crystal gold surfaces of various orientations.

Surface-enhanced Raman scattering (SERS) spectra are accompanied by broad background emission, which limits improvements in the signal-to-noise ratio. Despite the close correlation between the background generation and the SERS enhancement, the chemical origin of the background emission has remained somewhat mysterious. In this work, SERS spectra of organic monolayers are systematically measured on an atomically defined single crystalline gold surface of various orientations, which specifically define metal-molecule chemical interactions. The use of sphere-plane type plasmonic nanogap structures on a well-defined surface enables us to evaluate the contribution of charge transfer resonances to SERS enhancement. The present results not only reveal that charge transfer resonance at metal-molecule interfaces increases the intensity of plasmon-mediated broadband emission but also provide us a consistent view about electronic structures of metal-molecule interfaces.

Plasmonically nanoconfined light probing invisible phonon modes in defect-free graphene.

We present a simple plasmonic method that enables tuning of accessibility to the dipole-forbidden transition states of matter. This technique is realized by well-controlled plasmonic dimers, which can confine optical fields on the order of molecular dimensions. As an example, the approach is applied to activate invisible noncenter phonon modes of defect-free graphene in resonance Raman spectra. The relative intensity of the normally forbidden modes with respect to the dipole allowed modes progressively increases as the degree of field confinement increases. This opens up a novel avenue for both photochemical excitation of molecular systems and nanoscale characterization of materials.

Single molecule dynamics at a mechanically controllable break junction in solution at room temperature.

The in situ observation of geometrical and electronic structural dynamics of a single molecule junction is critically important in order to further progress in molecular electronics. Observations of single molecular junctions are difficult, however, because of sensitivity limits. Here, we report surface-enhanced Raman scattering (SERS) of a single 4,4'-bipyridine molecule under conditions of in situ current flow in a nanogap, by using nano-fabricated, mechanically controllable break junction (MCBJ) electrodes. When adsorbed at room temperature on metal nanoelectrodes in solution to form a single molecule junction, statistical analysis showed that nontotally symmetric b(1) and b(2) modes of 4,4'-bipyridine were strongly enhanced relative to observations of the same modes in solid or aqueous solutions. Significant changes in SERS intensity, energy (wavenumber), and selectivity of Raman vibrational bands that are coincident with current fluctuations provide information on distinct states of electronic and geometrical structure of the single molecule junction, even under large thermal fluctuations occurring at room temperature. We observed the dynamics of 4,4'-bipyridine motion between vertical and tilting configurations in the Au nanogap via b(1) and b(2) mode switching. A slight increase in the tilting angle of the molecule was also observed by noting the increase in the energies of Raman modes and the decrease in conductance of the molecular junction.

Selective dehybridization of DNA-Au nanoconjugates using laser irradiation.

Plasmonic heating to trigger release of oligonucleotides from nanoconjugates is potentially useful for therapeutic purposes and designed assembly of DNA nanostructures. In the past, great controllability has been achieved by introducing distinctive absorption nanoparticle centers, where the anchoring bond (e.g., sulfur-gold bond) has been selectively broken. Instead of releasing the surface-bound duplex DNA via breakage of the gold-sulphur anchor bond, selective and non-destructive dehybridization of DNA under a "mild" condition on different gold nanoconjugates is demonstrated in this work. This finding will permit sequential dehybridization/release of DNA at specific regions of a complex system; thus it can be extended to control gene expression and to manipulate an assembly of highly organized DNA constructs. Particularly we show herein the feasibility of selectively dehybridizing DNA-Au nanoconjugates via localized plasmonic heating, which is accomplished by controlling the laser wavelength, power, and irradiation time.

[Comparison of heparin-induced prolongation of APTT in 12 different laboratories in Kyushu area].

APTT is widely used for serial monitoring of treatment with unfractionated heparin. However, since its sensitivity to heparin varies significantly from one reagent to another, it is suggested that the therapeutic range had to be defined for each brand of APTT reagents. In this study, to investigate the affect of these variables, we compared various reagents of APTT and instruments for APTT measurements in different laboratories of university hospitals and related hospitals in Kyushu area. Same sample of normal pooled plasma added unfractionated heparin were measured in each laboratory. Prolongation of APTT by unfractionated heparin differed between laboratories. In addition, we examined prolongation of APTT by unfractionated heparin in normal plasma obtained from single donor. The prolongation of APTT differed between single donor samples even in the using of single APTT reagent and instrument. No correlation was observed between prolongation ratio of APTT and antithrombin concentration. These results indicate that sensitivity to heparin varies between individual in addition to brand of APTT reagent.

Probing collective terahertz vibrations of a hydrogen-bonded water network at buried electrochemical interfaces.

The exceptional properties of liquid water such as thermodynamic, physical, and dielectric anomalies originate mostly from the hydrogen-bond networks of water molecules. The structural and dynamic properties of the hydrogen-bond networks have a significant impact on many biological and chemical processes in aqueous systems. In particular, the properties of interfacial water molecules with termination of the network at a solid surface are crucial to understanding the role of water in heterogeneous reactions. However, direct monitoring of the dynamics of hydrogen-bonded interfacial water molecules has been limited because of the lack of a suitable surface-selective spectroscopic means in the terahertz (THz) frequency range where collective vibrations of water exist. Here we show that hydrogen-bond vibrations below 9 THz can be measured in situ at an electrochemical interface, which is buried between two THz-opaque media, by using a density of states format of surface-enhanced inelastic light scattering spectra. The interpretation of the obtained spectra over the range 0.3-6 THz indicates that the negatively charged surface accelerates collective translational motions of water molecules in the lateral direction with the increase of hydrogen-bond defects. Alternatively, the positively charged surface results in suppression of lateral mobility. This work gives a new perspective on in situ spectroscopic investigations in heterogeneous reactions.

In-situ Surface-Enhanced Raman Spectroscopy Reveals a Mars-van Krevelen-Type Gas Sensing Mechanism in Au@SnO2 Nanoparticle-Based Chemiresistors.

Molecular-level understandings of gas sensing mechanisms of oxide-based chemiresistors are significant for designing high-performance gas sensors; however, the mechanisms are still controversial due to the lack of direct experimental evidence. This work demonstrates efficient in situ surface-enhanced Raman spectroscopy (SERS) tracing of the highly representative SnO2-ethanol gas sensing using Au@SnO2 nanoparticles (NPs), where the Au core and SnO2 shell provide SERS activity and a gas sensing response, respectively. The in situ SERS evidence suggests that the sensing follows a Mars-van Krevelen mechanism rather than the prevailing adsorbed oxygen (AO) model. This mechanism is also observed in sensing other gases based on the Au@SnO2 NPs, showing its universality. This work offers efficient in situ tracing for gas sensing and experimental elucidation of the specific gas sensing mechanism, potentially ending the long-term controversy over the gas sensing mechanisms. Therefore, it is highly significant to this field.

Optical antenna for photofunctional molecular systems.

Optical antennas can enhance the efficiency of photon-molecule interactions. To design efficient antenna structures, it is essential to consider physicochemical aspects in addition to electromagnetic considerations. Specifically, chemical interactions between optical antennas and molecules have to be controlled to enhance the overall efficiency. For this purpose, sphere-plane nanostructures are suitable optical antennas for molecular-modified functional electrode systems when a well-defined electrode is utilized as a platform.

Crystal face dependent chemical effects in surface-enhanced Raman scattering at atomically defined gold facets.

Among electromagnetic and chemical (CM) contributions to surface-enhanced Raman scattering (SERS), the former is becoming controllable according to the recent progress in nanofabrication of plasmonic metal structures. However, it is still difficult to control the latter effect. Here, the degree of each contribution to SERS signals is examined on well-defined single crystalline facets of gold by using optical field localization within sphere-plane type plasmonic cavities. Crystal face dependent SERS studies of aminobenzenthiol adsorbates clearly show the distinction between CM enhancements on different surfaces, suggesting that the CM-activity of "SERS-hotspots" is closely related to interfacial dipoles formed at metal-molecular junctions.

[Evaluation of TB-beads assay utilizing the technique of magnetic beads--an innovative assay method for detection of acid fast bacilli].

The centrifuge method with the use of Semi-Alkalin Proteinase (SAP) and NALC-NaOH, recommended by the "2007 edition of the assay guideline for detection of Mycobacterium tuberculosis," has significantly contributed to improving the sensitivities and specificities of both smear and culture tests for detection of acid fast bacilli (AFB). However, this method poses some challenges in terms of its cumbersome and time-consuming assay protocol. "TB-beads (Kyokuto Pharmaceutical Industrial Co., Ltd.)" is a newly-developed method for detection of AFB utilizing magnetic beads. We evaluated the quality of this method in comparison with the centrifuge method, focusing on the results of smear and culture tests. This evaluation study was conducted using both 5 positive and 5 negative sputum samples. The sensitivity of TB-beads for fluorescent smear tests, conducted using "Acri-stain," was almost the same as that of the centrifuge method. One advantage of TB-beads, however, was that it was very convenient to practice microscopic observation due to the clear background of the smeared glass slides. The comparison of the contamination rates between the two methods showed that TB-beads suggested significantly lower contamination rates. The centrifuge method resulted in 50% and 60% of contamination rates for HK Semisolid Isolation Medium and BacT/ALERT MP, respectively. On the other hand, the contamination rates of TB-beads for both of the culture methods were only 10%. With regard to the 5 positive sputum samples, the comparison of the detection rates between the centrifuge and TB-Beads method was made utilizing Myco Acid, Ogawa K, and BacT/ALERT MP. The TB-Beads method suggested higher detection rates for Myco Acid and Ogawa K, while there were no significant differences between the two methods for BacT/ALERT MP (16-23 days). TB-beads is an easy method that allows to simplify the process of smear tests, and contributes to significantly reducing the contamination rate of culture tests. It also contributes to improving the sensitivity and detection rate of AFB testing. Furthermore, it does not require centrifugation. Ultimately, TB-beads is an innovative, safe, and convenient testing method for detection of AFB, which enables laboratory technicians to save time for routine work.