SERS of cylindrospermopsin cyanotoxin: Prospects for quantitative analysis in solution and in fish tissue.

Cylindrospermopsin (CYN), a cyanotoxin occurring in environmental waters as a cyanobacteria metabolite, has recently raised increased interest both in the scientific community and the environmental, food control and health care bodies due to the incidence of poisoning reports and the lack of prompt, effective detection and monitoring techniques. Here we report comprehensive Raman and SERS spectroscopy data on CYN cyanotoxin and provide a detailed characterization of the vibrational Raman signal based on DFT calculation as well as the adsorption properties with respect to the silver nanoparticles surface. Quantitative SERS analysis was achieved for concentrations range from 0.218 nM to 2.18 µM in aqueous solution. We further investigated the SERS discrimination of artificially intoxicated fish tissue from normal one, using linear discriminant analysis. Significant changes in SERS signal of toxic tissue compared to normal one allowed clear and fast differentiation of toxic tissue with 100% specificity/sensitivity. The cross-validation procedure provided 100% clear separation based on the SERS data. The results open reliable perspectives for SERS monitoring the environmental water bodies.

Rapid and noninvasive diagnosis of oral and oropharyngeal cancer based on micro-Raman and FT-IR spectra of saliva.

Fast, sensitive, and noninvasive techniques are needed for better health care management, particularly when traditional biopsies could be replaced with appropriate analyses of body fluids, such as saliva. Here is presented a proof-of-concept study, which aims to test a recently developed saliva samples preparation method, for oral and oropharyngeal cancer diagnosis, using micro-Raman and Fourier transform infrared (FT-IR) spectroscopic techniques. The detected biomarker bands and the cancer classification rates are compared and discussed. Saliva samples were collected from healthy donors and pathologically confirmed oral and oropharyngeal cancer patients. Principal components analysis (PCA) and principal components analysis-linear discriminant analysis (PCA-LDA) chemometric methods were applied to build discrimination models for the test and control groups. Based on the differences between salivary spectra of healthy and cancer patients, several biomarker bands were identified. Noteworthy, a significant vibrational biomarker band at 2064 cm-1, assigned to thiocyanate, was observed in both the FT-IR and Raman data-set. Other cancer characteristic Raman bands were 754 cm-1 (tryptophan), 530 and 927 cm-1 (lysozyme), 1001 cm-1 (phenylalanine), while the FT-IR biomarker band was located at 1075 cm-1 (phosphodiester bonds stretching in DNA, RNA). The oral and oropharyngeal cancer was classified with an accuracy of 90% based on the micro-Raman data and 82% based on the FT-IR data set, respectively. The study showed that oral and oropharyngeal cancer can be differentiated from control saliva samples based on their respective micro-Raman and FT-IR spectral signatures, due to the biomolecular modifications induced by the disease.

Adsorption of 6-mercaptopurine and 6-mercaptopurine-ribosideon silver colloid: a pH-dependent surface-enhanced Raman spectroscopy and density functional theory study. II. 6-mercaptopurine-riboside.

Surface-enhanced Raman spectroscopy (SERS) has been applied to characterize the interaction of 6-mercaptopurine-ribose (6MPR), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutic concentrations and as function of the pH value. Therefore, a detailed vibrational analysis of crystalline and solvated (6MPR) based on Density Functional Theory (DFT) calculations of the thion and thiol tautomers has been performed. 6MPR adopts the thion tautomeric form in the polycrystalline state. The SERS spectra of 6MPR and 6-mercaptopurine (6MP) recorded on silver colloid provided evidence that the ribose derivative shows different adsorption behavior compared with the free base. Under acidic conditions, the adsorption of 6MPR on the metal surface via the N7 and possibly S atoms was proposed to have a perpendicular orientation, while 6MP is probably adsorbed through the N9 and N3 atoms. Under basic conditions both molecules are adsorbed through the N1 and possibly S atoms, but 6MP has a more tilted orientation on the silver colloidal surface while 6MPR adopts a perpendicular orientation. The reorientation of the 6MPR molecule on the surface starts at pH 8 while in the case of 6MP the reorientation starts around pH 6. Under basic conditions, the presence of the anionic molecular species for both molecules is suggested. The deprotonation of 6MP is completed at pH 8 while the deprotonation of the riboside is finished at pH 10. For low drug concentrations under neutral conditions and for pH values 8 and 9, 6MPR interacts with the substrate through both N7 and N1 atoms, possibly forming two differently adsorbed species, while for 6MP only one species adsorbed via N1 was evidenced.

Raman, SERS and theoretical studies of papaverine hydrochloride and its neutral species.

Density functional theory (DFT) calculations and an experimental vibrational characterization of papaverine hydrochloride were performed. The computed structural parameters agree very well with the experimental values of the related crystal structure. The pH dependent Raman and SERS spectra of papaverine hydrochloride were recorded and discussed with the assistance of our theoretical results (harmonical vibrational wavenumbers, Raman scattering activities, total electron density and Natural Population Analysis of the molecule) and the SERS surface selection rules. Two different adsorption geometries were found for the corresponding evidenced species of papaverine, protonated and neutral, respectively.

Vibrational properties of the free and adsorbed acridone.

Theoretical density functional theory (DFT) calculation, ab initio and experimental vibrational characterization of acridone were performed. The computed vibrational modes agree well with the experimental values of the related crystal structure. Surface enhanced Raman scattering (SERS) of acridone in silver colloids with different surface potential values was studied. FT-SERS spectrum of acridone revealed different adsorption behavior of the title compound on the silver particles.

Vibrational spectroscopy of betulinic acid HIV inhibitor and of its birch bark natural source.

Raman and IR spectra of betulinic acid (BA) (3beta-hydroxy-20(19) lupaen-28 oic acid) and of the natural birch bark have been successfully recorded and discussed. A high selectivity of the Raman technique was remarked for evidencing the betulin in the birch bark. Surface enhanced Raman spectrum (SERS) of BA on colloidal silver has been obtained. The presence and shifting of the symmetric stretching mode of the COO group in the SERS spectrum suggests a chemisorption of the steroid structure on the metallic particles.

Raman and surface enhanced Raman spectroscopy of 2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide labeled proteins: bovine serum albumin and cytochrome c.

2,2,5,5-Tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide (tempyo) labeled bovine serum albumin and cytochrome c at different pH values were prepared and investigated using Raman-resonance Raman (RR) spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy. The Raman spectra of tempyo labeled proteins in the pH 6.7-11 range were compared to those of the corresponding free species. The SERS spectra were interpreted in terms of the structural changes of the tempyo labeled proteins adsorbed on the silver colloidal surface. The tempyo spin label was found to be inactive in the Raman-RR and SERS spectra of the proteins. The alpha-helix conformation was concluded to be more favorable as the SERS binding site of bovine serum albumin. In the cytochrome c the enhancement of the bands assigned to the porphyrin macrocycle stretching mode allowed the supposition of the N-adsorption onto the colloidal surface.