Surface-enhanced raman scattering spectroscopy of resveratrol

We report here, for the first time, the surface-enhanced Raman scattering (SERS) spectra of resveratrol using KNO₃-aggregated citrate-reduced silver (Ag) colloids. The technique provided a substantial spectral enhancement and therefore good quality spectra of resveratrol at parts per million (ppm) concentrations. The detection limit was found to be <1 μM, equivalent to <0.2 ppm. The SERS profile additionally closely resembled its normal solid-state Raman spectrum with some changes in relative intensity. These intensity changes, together with a precise band assignment aided by density functional theory calculations at the B3LYP/6–31G(d) level, allowed the determination of the structural orientation of the adsorbed resveratrol on the surface of the metal nanoparticles. In particular, the SERS spectra obtained at different resveratrol concentrations exhibited concentration-dependent features, suggesting an influence of surface coverage on the orientation of the adsorbed molecules. At a high concentration, an adoption of close-to-upright orientation of resveratrol adsorbed on the metal surface through the p-OH phenyl ring is favoured. The binding structure is, however, altered at lower surface coverage when the concentration decreases to a tilted orientation with the trans-olefin C=C bond aligning closer to parallel to the surface of the Ag nanoparticles.

Compression and probing C−H···I hydrogen bonds of iodoform under high pressure by x-ray diffraction and raman scattering

High-pressure methods were applied to investigate the structural stability and hydrogen bonding of polar molecules of iodoform by synchrotron radiation X-ray diffraction and Raman spectra measurements, respectively. Up to a pressure of 40 GPa, no phase transitions were observed. The discontinuous frequency shift of the C−H stretching band is believed to be related to the enhancement of the C−H···I weak hydrogen bonds under high pressures. Ab initio calculations were performed, and the results predict the frequency shift of the C−H stretching vibration as C−H···I interacts via hydrogen bonding. The bulk modulus is 17.3 ± 0.8 GPa, with a pressure derivative of 5.2.

Surface enhanced Raman scattering (SERS) fabrics for trace analysis

Flexible SERS active substrates were prepared by modification of silk fabrics with gold nanoparticles. Gold nanoparticles were in-situ synthesized after heating the silk fabrics immersed in gold ion solution. Localized surface plasmon resonance (LSPR) properties of the treated silk fabrics varied as the concentration of gold ions changed, in relation to the morphologies of gold nanoparticles on silk. In addition, X-ray diffraction (XRD) was used to observe the structure of the gold nanoparticle treated silk fabrics. The SERS enhancement effect of the silk fabrics treated with gold nanoparticles was evaluated by collecting Raman signals of different concentrations of p-aminothiophenol (PATP), 4-mercaptopyridine (4-MPy) and crystal violet (CV) solutions. The results demonstrate that the silk fabrics corresponding to 0.3 and 0.4 mM of gold ions possess high SERS activity compared to the other treated fabrics. It is suggested that both the gold content and morphologies of gold nanoparticles dominate the SERS effect of the treated silk fabrics.

Boron nitride nanosheet-veiled gold nanoparticles for surface-enhanced raman scattering

Atomically thin boron nitride (BN) nanosheets have many properties desirable for surface-enhanced Raman spectroscopy (SERS). BN nanosheets have a strong surface adsorption capability toward airborne hydrocarbon and aromatic molecules. For maximized adsorption area and hence SERS sensitivity, atomically thin BN nanosheet-covered gold nanoparticles have been prepared for the first time. When placed on top of metal nanoparticles, atomically thin BN nanosheets closely follow their contours so that the plasmonic hot spots are retained. Electrically insulating BN nanosheets also act as a barrier layer to eliminate metal-induced disturbances in SERS. Moreover, the SERS substrates veiled by BN nanosheets show an outstanding reusability in the long term. As a result, the sensitivity, reproducibility, and reusability of SERS substrates can be greatly improved. We also demonstrate that large BN nanosheets produced by chemical vapor deposition can be used to scale up the proposed SERS substrate for practical applications.

Simulation of a device concept for noninvasive sensing of blood glucose levels

This paper introduces a method of modeling noninvasive glucose sensing for patients who suffer from diabetes mellitus. The proposed technique involves simulation of light propagation through biological tissue with an embedded photonic crystal. The proposed detection technique is Raman spectroscopy and the use of the photonic crystal enables the enhancement of Raman scattering by engineering the photon density of states. Further enhancement can be achieved using noble metal clusters which result in surface enhanced Raman scattering and has the ability to provide enhancements of up to a million times.

Boron nitride nanosheets as improved and reusable substrates for gold nanoparticles enabled surface enhanced Raman spectroscopy.

Atomically thin boron nitride (BN) nanosheets have been found to be excellent substrates for noble metal particles enabled surface enhanced Raman spectroscopy (SERS), thanks to their good adsorption of aromatic molecules, high thermal stability and weak Raman scattering. Faceted gold (Au) nanoparticles have been synthesized on BN nanosheets using a simple but controllable and reproducible sputtering and annealing method. The size and density of the Au particles can be controlled by sputtering time, current and annealing temperature etc. Under the same sputtering and annealing conditions, the Au particles on BN of different thicknesses show various sizes because the surface diffusion coefficients of Au depend on the thickness of BN. Intriguingly, decorated with similar morphology and distribution of Au particles, BN nanosheets exhibit better Raman enhancements than silicon substrates as well as bulk BN crystals. Additionally, BN nanosheets show no noticeable SERS signal and hence cause no interference to the Raman signal of the analyte. The Au/BN substrates can be reused by heating in air to remove the adsorbed analyte without loss of SERS enhancement.

Au-Ag三角纳米环单层膜的原位转化制备及SERS效应

A gold-silver nanoframe monolayer nanostructure was obtained on the glass slide using the in-situ sacrificial template reaction. First the silver nanoprisms(~79.2 nm edge length) were prepared as the sacrificial template and were assembled on the slides through electrostatic interactions. The chloroautric acid in-situ reacted with the silver nanoprisms as oxidant. We evaluated the effect of oxidation reaction time on the morphologies and the LSPR properties of the prepared nanoframes. The thickness of gold-silver framework can be adjusted from 29.3 nm to 16.2 nm. We applied the gold-silver framework monolayer as a new surface-enhanced Raman scattering(SERS) substrate for determining 4-aminothiophenol.

Network management in distributed systems

Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices.

Developing lspr design guidelines

Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices

High-pressure spectroscopic study of hydrous and anhydrous Cs-exchanged natrolites

Structural phase transitions in hydrous Cs-exchanged natrolite (Cs-NAT-hyd) and anhydrous Cs-exchanged natrolite (Cs-NAT-anh) have been investigated as a function of pressure and temperature using micro-Raman scattering and synchrotron infrared (IR) spectroscopy with pure water as the penetrating pressure medium. The spectroscopic results indicate that Cs-NAT-hyd undergoes a reversible phase transition around 4.72 GPa accompanied by the discontinuous frequency shifts of the breathing vibrational modes of the four-ring and helical eight-ring units of the natrolite framework. On the other hand, we observe that Cs-NAT-anh becomes rehydrated at 0.76 GPa after heating to 100 °C and then transforms into two distinctive phases at 2.24 and 3.41 GPa after temperature treatments at 165 and 180 °C, respectively. Both of these high-pressure phases are characterized by the absence of the helical eight-ring breathing modes, which suggests the collapse of the natrolite channel and formation of dense high-pressure polymorphs. Together with the fact that these high-pressure phases are recoverable to ambient conditions, our results imply a novel means for radionuclide storage utilizing pressure and a porous material.