Measurement of lactose crystallinity using Raman spectroscopy

Raman spectroscopy (RS) was used to determine the crystallinity of lactose (a commonly used carrier in dry powder inhaler (DPI) formulations). Samples of α-lactose monohydrate and amorphous lactose were prepared using ethanol precipitation and lyophilisation respectively. The anomeric forms were confirmed using DSC at a rate of 10 °C/min and heated to 250 °C. The Raman spectra of both α-lactose monohydrate and amorphous lactose were obtained. Distinguishable differences were seen between the two spectra including peak areas and intensities. Depolarisation ratios (ρ) of each form were then determined to identify the crystallinity of the lactose carrier samples. At the prominent Raman bands 865 and 1082 cm−1, significant differences in ρ values were observed for crystalline (0.80 ± 0.07, 0.89 ± 0.06 respectively) and amorphous samples (0.44 ± 0.07, 0.51 ± 0.10).

Characterization of the moisture absorption and thermal ageing behaviour of polymeric composite systems using Raman spectroscopy

Advanced polymeric materials and their respective composites are fast becoming one of the world's most frequently used engineering materials. They find application in the manufacture of e.g. boat hulls, high performance motor vehicles, aircraft components and sports goods. Their high specific strength and specific stiffness give them the edge in applications where weight savings are critical, but their long-term durability is often questioned. These materials are susceptible to environmental conditions such as temperature and humidity. There is also a lack of relevant data, due to the long time-scales required for testing. In this study, the Raman technique has been used to monitor the degradation of two composite systems, namely: a rubber toughened vinylester material used in the marine industry and a high temperature bismaleimide/carbon fibre aerospace composite. Preliminary Raman studies show that the toughening rubber particles dispersed in the cured vinylester resin are leached out during hygrothermal ageing. The weight gain during ageing suggests that this leaching process occurs concurrently with the absorption of water molecules. An increase in the degree of cross-linking is observed when bismaleimide/carbon fibre composite is aged at high temperature. This cross- linking tendency decreases with increasing depth within the carbon fibre bundle.

Comparative analysis of surface-enhanced Raman spectroscopy of daidzein and formononetin

Phytoestrogens daidzein (4′,7-dihydroxy-isoflavone) and formononetin (4′-methoxy-7-hydroxy-isoflavone) have been studied by surface-enhanced Raman (SER) spectroscopy. Spectra were acquired in the presence of citratereduced silver colloids, over a range of pH and concentrations. Density functional theory calculations were used to assist assignment of the normal Raman spectra and help determine the mode of interaction of isoflavones with the silver nanoparticles. Formononetin does not show SER activity unless the 7-OH group is deprotonated, and accordingly, the interaction with the silver surface occurs via the deprotonated site. Daidzein, on the other hand, appears to contain multiple species at the surface, interacting via both the hydroxyl groups at 7-OH and 4′-OH, after deprotonation. This is an important result that points to potential future SERS applications in phytoestrogen analysis and provides a foundation for understanding the SER spectra of isoflavones.

Analysis of 5-hydroxyisoflavones by surface-enhanced Raman spectroscopy : genistein and methoxy derivatives

A series of 5-hydroxy-isoflavones—genistein, biochanin A, prunetin, and 4′,7-dimethoxygenistein—have been studied by surface-enhanced Raman spectroscopy (SERS). Citrate reduced silver colloids were employed as a standard technique to measure SER spectra over a range of pH and concentrations. Density functional theory calculations were used to assist in determining the mode of interaction of isoflavones with the silver nanoparticles. It is revealed that biochanin A and prunetin interact with the silver nanoparticles upon deprotonation of the 7- and the 4′-OH groups, respectively, to show SERS activity. Correlations of their spectra with SERS of genistein strongly support the presence of multiple interaction modes involving both of the OH groups in genistein, in a similar manner to daidzein. Surprisingly, however, under these conditions, the 5-OH group was found to be noninteractive as revealed by attempts to measure SERS of 4′,7-dimethoxygenistein. This was attributed partly to the low solubility and, more importantly, to the influence of steric hindrance, caused by the position of the pendant phenyl ring, which prevented interaction with the Ag colloid surface. These results complement recent work on daidzein and formononetin and provide further insight into understanding the SER spectra of isoflavones.

Dielectrophoresis-Raman spectroscopy system for analysing suspended nanoparticles

A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO₃) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water.

Dielectrophoresis-raman spectroscopy system for analysing suspended WO3 nanoparticles

Dielectrophoresis (DEP) utilizing a curved microelectrode pattern was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a Raman transparent quartz substrate, and integrated with a microfluidic channel in poly-dimethylsiloxane (PDMS). This integrated system can be efficiently used for the determination of suspended particles type and the direct mapping of their spatial concentrations. It will be demonstrated that the integration of Raman mapping with dielectrophoretically controlled WO3 particles can be used for studying suspended particles in situ.

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.

Boron nitride nanosheets improve sensitivity and reusability of surface-enhanced raman spectroscopy

Surface enhanced Raman spectroscopy (SERS) is a useful multidisciplinary analytic technique. However, it is still a challenge to produce SERS substrates that are highly sensitive, reproducible, stable, reusable, and scalable. Herein, we demonstrate that atomically thin boron nitride (BN) nanosheets have many unique and desirable properties to help solve this challenge. The synergic effect of the atomic thickness, high flexibility, stronger surface adsorption capability, electrical insulation, impermeability, high thermal and chemical stability of BN nanosheets can increase the Raman sensitivity by up to two orders, and in the meantime attain long-term stability and extraordinary reusability not achievable by other materials. These advances will greatly facilitate the wider use of SERS in many fields.

Electrochemical synthesis of fractal bimetallic Cu/Ag nanodendrites for efficient surface enhanced Raman spectroscopy.

Here, we for the first time synthesized bimetallic Cu/Ag dendrites on graphene paper (Cu/Ag@G) using a facile electrodeposition method to achieve efficient SERS enhancement. Cu/Ag@G combined the electromagnetic enhancement of Cu/Ag dendrites and the chemical enhancement of graphene. SERS was ascribed to the rough metal surface, the synergistic effect of copper and silver nanostructures and the charge transfer between graphene and the molecules.

Self-assembly of ultrathin gold nanowires and single walled carbon nanotubes as a highly sensitive substrate for surface enhanced Raman spectroscopy

Here we report self-assembly of ultrathin gold nanowires and single-walled carbon nanotubes with an ultrahigh aspect ratio as a highly sensitive substrate for surface enhanced Raman spectroscopy. And we demonstrated that the hybrids were especially efficient in adsorption of aromatic molecules such as 4-mercaptobenzoic acid and the hybrids materials could be used as a novel platform for trace level detection in the verification of paper notes through the Raman enhancement technique.