Quantitative analysis of methyl green using surface-enhanced resonance Raman scattering

Optimized Tapered Fiber Decorated by Ag Nanoparticles for Raman Measurement with High Sensitivity

A tapered fiber decorated by Ag nanoparticles is prepared as a surface-enhanced Raman scattering (SERS) substrate. There are two key parameters during the preparation process, the fiber cone angle and the density of decorated AgNPs on the fiber tip surface. Their theoretical analysis on the forming mechanism and the optimization process is studied in detail. The tapered fibers with angles from 0.5 to 30° are successfully prepared, with a chemical method in a small tube using a bending interface. AgNPs with different densities are decorated on the surface of the tapered fibers with an electrostatic adsorption method. The optimized tapered fiber SERS probe with an angle of 12° and AgNPs density of 26.67% provides the detection of Rhodamine 6G (R6G) with 10⁻¹⁰ mol/L.

Dynamic Monitoring of the Oxidation Process of Phosphatidylcholine Using SERS Analysis

Phosphatidylcholine oxidation is closely related to many neurodegenerative diseases. In this paper, Raman spectroscopy was proposed to continuously monitor the oxidation of phosphatidylcholine and provide deep understanding of this biochemical process. To increase the detection sensitivity, surface-enhanced Raman spectroscopy (SERS) with a micro-nanosilver-complex substrate was prepared by electrodeposition. The prepared SERS substrate had an enhancement factor as high as 7.8 × 10⁷, ensuring detection sensitivity in the phosphatidylcholine-oxidation process. It was illustrated that the oxidation of phosphatidylcholine in an ethanol-water solution under the experimental conditions could be monitored and well described by second-order kinetics by continuously measuring and analyzing the SERS spectra of phosphatidylcholine-oxidation intermediates in 20 days. Meanwhile, the oxidation products were confirmed by mass spectrometry, and the oxidation process was in good concordance with mass-spectrometry detection. The use of SERS in following a biochemical process has advantages, including simple instrumentation, a low cost, a short detection time, and no sample pretreatment. Therefore, as a kind of vibration spectrum, SERS is preferable to traditional detection approaches such as MS, HPLC, and MRI for the dynamic monitoring and analysis of complex biochemical processes.

Simultaneous multiplexed quantification of caffeine and its major metabolites theobromine and paraxanthine using surface-enhanced Raman scattering

Accurate quantitative measurement of drugs and their metabolites is important as this can be used to establish long-term abuse of illicit materials as well as establish accurate drug dosing for legal therapeutics. However, the levels of drugs and xenometabolites found in human body fluids necessitate methods that are highly sensitive as well as reproducible with the potential for portability. Raman spectroscopy does offer excellent reproducibility, portability and chemical specificity, but unfortunately, the Raman effect is generally too weak unless it is enhanced. We therefore developed surface-enhanced Raman scattering (SERS) and combined it with the powerful machine learning technique of artificial neural networks to enable rapid quantification of caffeine and its two major metabolites theobromine and paraxanthine. We established a three-way mixture analysis from 10⁻⁵ to 10⁻⁷ mol/dm³, and excellent predictions were generated for all three analytes in tertiary mixtures. The range we selected reflects the levels found in human body fluids, and the typical errors for our portable SERS analysis were 1.7 × 10⁻⁶ mol/dm³ for caffeine, 8.8 × 10⁻⁷ mol/dm³ for theobromine and 9.6 × 10⁻⁷ mol/dm³ for paraxanthine. We believe this demonstrates the exciting prospect of using SERS for the quantitative analysis of multiple analytes simultaneously without recourse to lengthy and time-consuming chromatography, a method that often has to be combined with mass spectrometry.

Simultaneous multiplexed quantification of nicotine and its metabolites using surface enhanced Raman scattering

We have developed a SERS approach that can simultaneously detect the drug nicotine along with its two major metabolites cotinine andtrans-3′-hydroxycotinine without recourse to lengthy chromatography.

Semi-quantitative analysis of gentian violet by surface-enhanced Raman spectroscopy using silver colloids

The viability of the application of surface-enhanced Raman spectroscopy (SERS) to the semi-quantitative analysis of the triphenylmethane dye gentian violet was examined by using activated borohydride-reduced silver colloids. Raman and SERS spectra of aqueous solutions of gentian violet at different pH values were acquired for the first time and equally intense SERS signals were obtained at both acidic and alkaline pH values. Two maxima intensities observed in the pH profile revealed the presence of different ionization states of the dye. The pH conditions for SERS were optimized over the pH range 1 to 12 and the biggest enhancement for SERS of this charged dye was found to be at pH 2.0; thus, this condition was used for semi-quantitative analysis. A good linear correlation was observed for the dependence of the signal intensities of the SERS bands at 1620 cm(-1) (R = 0.999) and 1370 cm(-1) (R = 0.952) on dye concentration over the range 10(-6) to 10(-4) mol/L, using laser excitation at 514.5 nm. At concentrations of dye above 10(-2) mol/L, the concentration dependence of the SERS signals is nonlinear. This is explained as due to the precipitation of metallic silver as well as due to saturation caused by complete coverage of the SERS substrate. A series of intensities of the band at 1620 cm(-1) measured from dye molecules proved that the single-molecule limit of gentian violet is attained at the concentration of 10(-9) mol/L.