Natalia E. Markina

Detection of sulfonamide drug in urine using liquid-liquid extraction and surface-enhanced Raman spectroscopy

In this article we have applied liquid-liquid extraction (LLE) as a sample preparation technique for detection of sulfadimethoxine (one of sulfonamide drugs) in urine using surface-enhanced Raman spectroscopy (SERS). SERS substrate based on silver nanoparticles has been prepared by citrate reduction of silver nitrate. Obtained calibration curve (SERS intensity vs. sulfadimethoxine concentration) has been used for detection of sulfadimethoxine in human urine samples artificially contaminated by sulfadimethoxine. Three different solvents (ethyl acetate, diethyl ether, chloroform) have been used for LLE performance tests. Chloroform being found as the most effective one based on calculation of recoveries after SERS measurements. Thus we would like to propose fast (less than 20 minutes), simple and sensitive (detection limit up to 1 μg/ml) test for detecting sulfa drugs in urine using a combination of SERS with LLE with sample volume as low as 100 μL. Such test can be applied for evaluation of the degree of drug extraction from human body and half-life of such drug applied in the course of therapeutic treatments of certain diseases.

Multifunctional silver nanoparticle-doped silica for solid-phase extraction and surface-enhanced Raman scattering detection

AbstractMultifunctional silica gel with embedded silver nanoparticles (SiO2–AgNP) is proposed for application as sorbent for solid-phase extraction (SPE) and simultaneously as substrate for surface-enhanced Raman spectroscopy (SERS) due to their high sorption properties and ability to enhance Raman signal (SERS-active sorbents). SiO2–AgNP was synthesized via alkaline hydrolysis of tetraethyl orthosilicate with simultaneous reduction of silver ions to silver nanoparticles (AgNP) within the SiO2 bulk. Synthesis of AgNP directly to the SiO2 matrix enables to exclude any additional stabilizers for the nanoparticles that educes signal-to-noise ratio during SERS measurement. Apart from Raman spectroscopy, obtained sorbents were also characterized by scanning electron microscopy and UV-visible diffuse reflectance spectroscopy. The influence of AgNO3 concentration used during the SiO2–AgNP synthesis on its gelling time, color, diffuse reflectance spectra, and enhancement of Raman signal was investigated. A Raman enhancement factor of SiO2–AgNP with optimal composition was around 105. Finally, the sorbents were applied for SPE and subsequent SERS detection of model compounds (rhodamine 6G and folic acid). It was found that SPE enables to decrease detectable concentrations by two orders. Therefore, SPE combined with SERS has high potential for further analytical investigations. Graphical abstractᅟ

Influence of bending of monoatomic copper chains with 10 and 22 atoms on their absorbance spectra: TD-DFT calculations

The aim of the work is the investigation of bending on the properties of hypothetical one-atom-thick copper clusters (CC) (with 10 and 22 atoms). Time-dependent density functional theory with PBE0 functional and lanl2dz basis set were used for all calculations. The bending was performed by changing angle between copper atoms from 180° to 144° and 163.7° (2° step size) for CC with 10 and 22 atoms, correspondingly. The dependences of absorbance spectra in UVvisible-NIR range (400-2000 nm range) and various energetic characteristics (final energy, chemical potential, and binding energy) on bending angle were investigated. Non-bended (linear) clusters were assigned as references. First, absorbance spectra of all CC contain interband transitions (3d→4sp) in UV-visible range (below 600 nm). Linear configuration of CC also contain intensive absorbance band in NIR region (at 900 and 1700 nm for CC with 10 and 22 atoms) which is associated with 4s electron oscillations along clusters (longitudinal transitions). Significant dumping of low energy 4s transitions (HOMO→LUMO) and interband transitions in the range 600‒500 nm was observed during the bending of CC. Obtained results are in agreement with experimental results for 2D copper nanostructures from literature. We explain such influence of bending by formation merging 4s orbitals which form new 4s oscillations in-plane of bending (in the case of ring-like CC – diametral oscillations). An influence of bending on energy, stability, and chemical potential (Fermi level) of CC was also investigated and discussed.

Synthesis of SERS-nanotags and their investigation inside photonic crystal fiber

The aim of this work was the fabrication of nanolabels (SERS-nanotags) which are used for chemical analysis by means of surface-enhanced Raman spectroscopy (SERS), and registration of their SERS spectra inside photonic crystal fibers (PCF). The SERS nanotags fabrication included synthesis of silver nanoparticles with subsequent deposition of Raman active layer (thiol-group contained aromatic compound) and protecting layer composed of silica shell. Finally, SERS spectra of the SERS nanotags were registered inside PCF in order to determine the value of fiber-enhancement of the Raman signal and to estimate analytical potential of this combination.

Detection of rhodamine 6G in blood and urine using combination of surface-enhanced Raman spectroscopy and liquid-liquid extraction

The aim of this report is detection of model compound, rhodamine 6G (R6G), in blood and urine samples using surfaceenhanced Raman spectroscopy (SERS) as a detection tool and liquid-liquid extraction (LLE) for improving quality of SERS analysis (SERS-LLE combination). SERS substrate is a plasmonic nanomaterial which possesses drastic increasing of Raman spectrum intensity (106‒108) of any molecule adsorbed onto its surface. Here we used citrate stabilized silver nanoparticles as SERS substrate and synthesized them applying wet chemical approach. Before SERS measurements, blood and urine samples were artificially contaminated with R6G using 50 and 500 ng/mL concentrations for both samples. In order to reduce detectable concentrations of R6G and improve signal-to-noise ratio, we applied LLE which allows us to separate R6G from the matrix mixture and increase the analyte concentration. Four different LLE protocols were used and the most efficient one was found. Obtained results showed usefulness of SERS-LLE combination for chemical analysis of body fluids with level of detectable concentration down to tens ng/mL.

New SERS-active alumina-based sorbents containing Ag nanoparticles

New SERS-active materials were obtained by preparation of alumina with embedded silver nanoparticles and their application both as sorbents for pre-concentration and SERS platforms was studied. The influence of ionic strength on Ag NPs size, absorption spectra and SERS signal was investigated. Synthesized materials were examined by Raman spectroscopy, scanning electron microscopy, and UV-visible spectroscopy. The optimal conditions for SERSmeasurements were chosen. Synthesized materials were applied for pre-concentration of model analytes (Rhodamine 6G, folic acid and pyrene) and their SERS detection directly within the sorbent. It was shown that the recovery of analytes could be improved by alumina modification. The combination of surface-enhanced Raman spectroscopy with preconcentration is a promising instrument for analytical applications.