Plasmonic photocatalytic degradation of tebuconazole and 2,4-dichlorophenoxyacetic acid by Ag nanoparticles-decorated TiO2 tracked by SERS analysis.

Chemical oxidation technologies have been notably used for the mineralization of organic pollutants from aqueous effluents, been especially relevant for the degradation of pesticides. In this context, both tebuconazole (TEB) and 2,4-dichlorophenoxyacetic acid (2,4-D) pesticides were photodegraded by a combined catalyst of TiO2 and silver nanoparticles irradiated by UV-A light (λmax = 368 nm), and the experiments were tracked by surface-enhanced Raman scattering (SERS) spectroscopy. For 2,4-D, the degradation of about 70% was observed after almost 200 min, while for TEB, a decrease of 80% of the initial concentration was observed after approximately 100 min. The SERS monitoring allowed the proposal of some by-products, such as oxidized aliphatic chain and triazole from TEB besides glycolic, glyoxylic and dihydroxyacetic acids from 2,4-D. Their toxicities were predicted through ECOSAR software, verifying that most of them were not harmful to populations of fish, Daphnia and green algae. Thus, the performed oxidative process was efficient in the photodecomposition of TEB and 2,4-D pesticides, inclusive in terms of the decreasing of the toxicity of contaminated effluents.

Tracking chemical interactions of folic acid on gold surface by SERS spectroscopy.

Surface-enhanced Raman scattering (SERS) spectroscopy was used in the investigation of the adsorption of folic acid (FA) on the surface of gold nanoparticles (AuNPs) in the absence and presence of surface modifiers hydrochloride acid (HCl) and 1-mercaptoethanol (ME). The proposal for the chemical interactions of FA with the metallic surface was based on vibrational assignment supported by Density Functional Theory (DFT) calculations. In the absence of surface modifiers, FA interacts with the gold surface through the pteridine moiety in a tilted geometry. In the presence of ME, the molecule of FA is anchored through hydrogen bonds with the surface modifier. The presence of HCl induced ion-pair interactions involving chloride ions, adsorbed on gold surfaces, and both the nitrogen N1 of the pteridine ring and the γ-carboxylic acid of the glutamic acid moiety. In this condition, keto-enol equilibrium can be evidenced by a remarkable enhancement of marker bands in the SERS spectra.

Insights on the transport of tamoxifen by gold nanoparticles for MCF-7 breast cancer cells based on SERS spectroscopy.

Gold nanoparticles (AuNP) were synthesized and modified with anti-folate receptor antibody (AB), folic acid (FA), crystal violet (CV), poly (ethyleneglycol) methyl ether thiol and the antineoplastic drug tamoxifen (TAM). Such a preparation was incubated in vitro with MCF-7 human breast cancer cells, showing a decrease in the TAM dosage for the reduction of cell viability. The adsorption of TAM on gold surface was investigated by surface-enhanced Raman scattering (SERS) spectroscopy and the assignment based on Density Functional Theory calculations showed that the ether moiety was involved in the interactions with the metal. Such a chemical affinity was correlated with the carrying of TAM in the biological media. CV was included in the preparation as a molecular probe for SERS spectroscopy, whose signal was monitored to analyse the efficiency of the modified AuNP in the target of neoplastic cells. The results showed AB, FA and TAM components had complementary roles in the cell recognition and, therefore, in the efficiency of the drug carrier nanosystem.

The control of the adsorption of bovine serum albumin on mercaptan-modified gold thin films investigated by SERS spectroscopy.

Nanostructured gold thin films were built from deposition of colloidal gold nanoparticles on silanized glass slides, and used to study the adsorption of bovine serum albumin (BSA) after chemical treatment of gold surface with the mercaptans 2-mercaptoethanol, 3-mercaptoproprionic acid, 1,3-propanedithiol and 1-propanethiol. Surface-enhanced Raman scattering (SERS) spectroscopy was used for investigating the chemical interactions of BSA with the modified gold surfaces. In the presence of the surface modifier 2-mercaptoethanol, a promoter of hydrogen bonds, the stable interactions among BSA and gold surfaces led to high reproducibility of the SERS spectral pattern in the most monitored points of the mapped surface. The vibrational assignment endorsed the assumption that lysine residue, majority present in the molecular structure, were the principal anchor site of BSA involved in the interactions with 2-mercaptoethanol-modified gold surface.

Insights of adsorption mechanisms of Trp-peptides on plasmonic surfaces by SERS.

The adsorptions of tryptophan (Trp) on silver or gold surfaces were investigated by surface-enhanced Raman scattering (SERS) measurements. In addition, peptides with Trp in different chain positions were studied and the adsorption sites were determined based on marker bands. The indole ring was the main group responsible for the interactions with gold nanoparticles (AuNPs). In the presence of HCl, the SERS spectra suggested that the anchoring of such peptides on AuNPs was reinforced by ionic pair interactions between protonated amine and chloride ions. The adsorptions of Trp and its derivatives on silver nanoparticles (AgNPs) show some variability in the spectral patterns, even though the enhanced carboxilate and amino features were ever ascribed as preferable adsorption site. Based on DFT calculations the vibrational assignment allows the reinterpretation of previous published works. The investigations showed that both the high affinity of indole moiety for the AuNP surfaces make these substrates adequate for studying the adsorption of peptides containing Trp and the proposed SERS assignments could be helpful for further studies of more complex structures.

Surface-enhanced Raman scattering study of the redox adsorption of p-phenylenediamine on gold or copper surfaces.

The adsorption of the p-phenylenediamine (PPD(+)) radical cation on gold or copper nanoparticle (NP) surfaces was studied through surface-enhanced Raman scattering (SERS) spectroscopy, excited at 1064 nm. The SERS spectra were obtained from gold or copper NPs after exposure to non-oxidized p-phenylenediamine (PPD) aqueous solution, in millimolar concentration. The gold NPs were synthesized as nanoshells involving silica cores (SiO(2)@Au) and the copper NPs were obtained in aqueous medium, undergoing surface oxidation with the formation of Cu(II) oxide nanoshell (Cu@CuO). In the latter, the oxidative adsorption of PPD(+) led to the reduction of the copper oxide, present on NP surface, allowing obtaining the PPD(+) SERS spectrum. The vibrational assignments of the SERS spectra of the adsorbate were performed using the results of Density Functional Theory calculations of the Raman frequencies, which together with the SERS surface selection rules, allowed to infer the adsorption geometry of PPD(+) radical cation on both metallic surfaces. This work stress the investigation of redox processes involved in the molecular adsorption is imperative for the interpretation of the SERS results, which is even more important when copper surfaces are studied.

High performance gold nanorods and silver nanocubes in surface-enhanced Raman spectroscopy of pesticides.

The behavior of Au nanorods and Ag nanocubes as analytical sensors was evaluated for three different classes of herbicides. The use of such anisotropic nanoparticles in surface-enhanced Raman scattering (SERS) experiments allows the one to obtain the spectrum of crystal violet dye in the single molecule regime, as well as the pesticides dichlorophenoxyacetic acid (2,4-D), trichlorfon and ametryn. Such metallic substrates show high SERS performance at low analyte concentrations making them adequate for use as analytical sensors. Density functional theory (DFT) calculations of the geometries and vibrational wavenumbers of the adsorbates in the presence of silver or gold atoms were used to elucidate the nature of adsorbate-nanostructure bonding in each case and support the enhancement patterns observed in each SERS spectrum.

Investigations of different carbohydrate anomers in copper(II) complexes with D-glucose, D-fructose, and D-galactose by Raman and EPR spectroscopy.

With the aim of verifying different carbohydrate anomers coordinated to copper(II) ions, some copper(II) complexes with D-glucose (Glc), D-fructose (Fru), and D-galactose (Gal) were prepared and investigated by spectroscopic techniques. Their compositions were verified by elemental, ICP-AES and thermal analyses, in addition to conductivity measurements. The compounds isolated were consistent with the formula Na2[Cu2(carbohydrate)3].8H2O and Na[Cu2(carbohydrate)3].6H2O for the aldoses Glc and Gal, respectively, and Na2[Cu3(carbohydrate)4].8H2O in the case of the ketose, Fru. EPR spectra of these solids showed a rhombic environment around the metal center and suggested the presence of different anomers of the carbohydrates in each case. By Raman spectroscopy, it was possible to verify the predominance of the beta anomer of d-glucose in the corresponding copper complex, while in the free ligand the alpha anomer is predominant. In the case of the analogous complex with d-galactose, the spectrum of the complex shows bands of both anomers (alpha and beta) in approximately the same relative intensities as those observed in the isolated free ligand spectrum. On the other hand, for the complex with d-fructose a mixture of both furanose (five-membered ring) and pyranose (six-membered ring) structures was detected with prevalence of the furanose structure. Based on variations in the relative intensities of characteristic Raman bands, the binding site for copper in the fructose ligand was identified as most likely the 1-CH2OH and the anomeric 1-OH, while in beta-D-glucose it is presumably the anomeric 1-OH and the O-5 atom. These results indicated that EPR and Raman spectroscopy are suitable supporting techniques for the characterization of carbohydrate anomers coordinated to paramagnetic ions.