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We studied the surface-enhanced effect exerted by modified surfaces with Ag@SiO2 and Au@SiO2 core–shell nanoparticles on the photoluminescence of two chromium-doped spinels.

PhD CONICYT project 21150397 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1190246 CONICYT (Fondo de Equipamiento Cientifico y Tecnologico, FONDEQUIP) EQM140142

The pyren-1′-yl-functionalized dithiadiazolyl (DTDA) radical, C16H9CNSSN (1), is monomeric in solution and exhibits fluorescence in the deep-blue region of the visible spectrum (440 nm) upon excitation at 241 nm. The salt [1][GaCl4] exhibits similar emission, reflecting the largely spectator nature of the radical in the fluorescence process, although the presence of the radical leads to a modest quenching of emission (ΦF = 98% for 1+ and 50% for 1) through enhancement of non-radiative decay processes. Time-dependent density functional theory studies on 1 coupled with the similar emission profiles of both 1+ and 1 are consistent with the initial excitation being of predominantly pyrene π–π* character. Spectroscopic studies indicate stabilization of the excited state in polar media, with the fluorescence lifetime for 1 (τ = 5 ns) indicative of a short-lived excited state. Comparative studies between the energies of the frontier orbitals of pyren-1′-yl nitronyl nitroxide (2, which is not fluorescent) and 1 r...

The phenanthrene-functionalised dithiadiazolyl radical 2 provides a rare example of a fluorescent radical, exhibiting bright blue fluorescence (410 nm) in solution (MeCN: ΦF = 0.11). The indirect participation of the radical electron in the fluorescence process is supported by (i) TD-DFT studies and (ii) the observation that the diamagnetic salt [2][GaCl4] also exhibits a similar broad emission at 410 nm. The large Stokes shift appears associated with significant molecular relaxation in the excited state, evidenced by the solvent-independent nature of the absorption profile but marked solvent-dependent emission spectrum. Incorporation of 2 into polymer matrices such as PMMA or polystyrene leads to substantial enhancement in air stability with evidence of efficient emission quenching at higher w/w radical : polymer ratios.

The present work describes the characterization by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques of ITO modified electrodes with electrostatic assemblies (Polycation/Quantum Dots) and their use in the electro- and photoelectrocatalytic reduction of CO2. These assemblies were prepared with polycations poly-diallyldimethylammonium (PD) and poly-(2-trimethylammonium) ethyl methacrylate (PM) and nanocrystals of CdTe of 2.77 nm (Q2). The size of the nanocrystals was controlled by the synthesis reflux time and incorporated by electric field directed Layer-by-Layer assembly method (EFDLA). The polycations were characterised by NMR measurements; showing important effects on the electrostatic assemblies. PM modified electrodes, with its lower rigidity, exhibited less roughness than the PD modified electrodes, 8.0 nm versus 32.8 nm, and higher heterogeneity in its surface composition. Higher resistance to the charge transfer and time constants were obtained with PMQ2 modified electrode, 63.8 Ω cm−2 and 2.69 ms versus 49.30 Ω cm−2 and 1.3 ms for PDQ2. The electro- and photoelectro properties for CO2 reduction were studied through j-E curves and potential controlled electrolysis. Modified surfaces were active toward the reduction of CO2, with a positive shift of the activity between darkness and irradiation conditions, 0.050 V with PDQ2 and 0.450 V with PMQ2. The main product of the CO2 reduction was CH3OH, with traces of CO and HCOOH. The PM modified electrodes with QDs of 2.77 nm presented a selective behaviour for the production of CH3OH.

Made available in DSpace on 2018-12-11T17:37:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-09-15 Made available in DSpace on 2018-12-11T17:37:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-09-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Rare-earth-doped phosphors immobilized in polymeric matrices find many applications like LEDs. However, little emphasis has been paid to the phosphor and plasticizer effect on the polymer structural, morphological and spectroscopic properties, for the development of functional devices. In this study, we are reporting for the first time the use of Buriti Oil (BO), a natural oil, as plasticizer in Ba2SiO4:Eu3+-doped PVDF composites membranes. Both, Buriti oil and phosphor amount were varied in the membrane synthesis. The drying temperature at 60 °C leads to the formation of the α-PVDF and the increase of the amount of BO up to 400 μL decreases the PVDF crystallinity. Furthermore, the BO and phosphor additions increase the membrane thermal stability. Finally, the composite obtained with 10 wt% of Ba2SiO4:Eu3+ shows relative intense red emission with maximum at 612 nm originating from the Eu3+ radiative transitions in Ba2SiO4 lattice, making this composite material a good candidate for optical devices. São Paulo State University (Unesp) School of Technology and Sciences São Paulo State University (Unesp) Institute of Biosciences Humanities and Exact Sciences Universidad de Chile Facultad de Ciencias Departamento de Física, Las Palmeras São Paulo State University (Unesp) School of Technology and Sciences São Paulo State University (Unesp) Institute of Biosciences Humanities and Exact Sciences FAPESP: 2012/13876-9 FAPESP: 2015/10394-1 FAPESP: 2016/20421-9 CNPq: 307385/20159

We report shell-isolated nanoparticle-enhanced fluorescence (SHINEF) of CdTe quantum dots. Enhanced spectra are obtained after Ag SHINs were spread onto homogenous CdTe quantum dot/polyelectrolyte layer-by-layer (LbL) films on quartz. The thin silica shell of the SHINs effectively isolates the Ag cores, preventing short-range quenching to the metal and enabling plasmon enhancement of the quantum dot fluorescence (ca. 35 fold).

Shell-isolated nanoparticles (SHINs) nanostructures provide a versatile substrate where the localized surface plasmon resonances (LSPRs) are well-defined. For SHINEF, the silver (or gold) metal core is protected by the SiO2 coating, which is thicker than the critical distance for minimum quenching by the metal. In the present work, it is shown that an increase in the SHINEF enhancement factor may be achieved by inducing SHIN aggregation with electrolytes in solution. The proof of concept is demonstrated using NaCl as aggregating agent, although other inorganic salts will also aggregate SHIN nanoparticles. As much as a 10-fold enhancement in the SHINEF enhancement factor (EF) may be achieved by tuning the electrolyte concentrations in solution. The SHINEF experiments include the study of the aggregation effect controlling gold SHIN's surface concentration via spraying. Au-SHINs are sprayed onto layer-by-layer (LbL) and Langmuir-Blodgett (LB) films, and samples are fabricated using fluorophores with low and also high quantum yield.

Highly fluorescent nanoparticles, or quantum dots, have multiple applications in biology and biomedicine; however, in most cases, it is necessary to functionalize them to enhance their biocompatibility and selectivity. Generally, functionalization is performed after nanoparticle synthesis and involves the use of molecules or macromolecules having two important traits: specific biological activity and functional groups that facilitate nanoparticle capping (i.e. atom–atom interaction). For this reason, we carried out a simple protocol for the chemical synthesis of cadmium telluride quantum dots capped with glutathione, and we then functionalized these nanoparticles with the amphipathic peptide CLPFFD. This peptide attaches selectively to β-Amyloid fibres, which are involved in Alzheimer’s disease. Our results show that the optical properties of the quantum dots are not affected by functionalization with this peptide. Infrared spectra showed that cadmium telluride quantum dots were functionalized with the peptide CLPFFD. In addition, no significant differences were observed between the surface charge of the quantum dots with or without CLPFFD and the nanocrystal size calculated for HR-TEM was 4.2 nm. Finally, our results show that quantum dots with CLPFFD are stable and that they resulted in a significantly reduced cytotoxicity with respect to that induced by quantum dots not conjugated with the peptide. Moreover, the results show that the CLPFFD-functionalized nanoparticles bind to β-Amyloid fibres.

Extraction of Athyonidium chilensis body wall afforded a light brown powder in 4.2% yield which was fractionated by ion-exchange chromatography. The main fraction F1 contained glucuronic acid, galactosamine and fucose in a molar ratio of 1.0:1.1:1.1, and 32.9% of sulfate group. The second derivative FT-IR spectroscopy and Surface-enhanced Raman scattering (SERS) give more information than the normal IR and Raman spectroscopies. The broad band in the normal FT-IR spectrum of F1 at 850.6 cm−1 assigned to sulfate group was resolved in the second derivative spectrum into three bands at 856.4 cm−1, 837.4 cm−1 and 818.6 cm−1 assigned to sulfate group attached to axial C4 and equatorial C2 and C6, respectively, in glycosidic residues. The most important bands in SERS of F1, but not observed in Raman spectrum are bands at 1648 cm−1 (νC O), 1377 cm−1 (δC–H) assigned to methyl group of N-acetyl group, at 1173 cm−1 and at 956.2 cm−1 (νC–O–C) of glycosidic linkage; and bands at 925.5 cm−1 and 890.4 cm−1 (δC1–H) assigned to α and β anomeric configurations of glycosidic residues, respectively. By NMR studies, glycosidic linkages and sulfation pattern of F1 was confirmed. Results obtained indicated that fraction F1 is chondroitin 4,6-disulfate substituted at position O-3 of glucuronic acid by partially 2,4-disulfated α-fucopyranosyl residues. Moreover, the anticogulant activity, measure in APTT of F1 showed at low concentration, a good correlation with heparin.

Coated silver (Ag) colloids synthesized with D-glucose permit the observation of surface-enhanced fluorescence (SEF) and surface-enhanced resonance Raman scattering (SERRS) of the rhodamine B (RhB) molecule. The organic coating formed during the synthesis of the Ag nanostructures was identified by its surface-enhanced Raman scattering (SERS) spectrum as D-gluconic acid. The RhB molecule is used to exemplify the distance dependence of SEF and SERRS on the coated Ag nanostructures. The fluorescence enhancement factor for RhB on D-gluconic acid coated silver nanoparticles was determined experimentally and estimated using a simple model. Further support for the plasmon enhancement is obtained from the fact that the measured fluorescence lifetime of RhB on the silver coated with D-gluconic acid is shorter than that found on a glass surface. A very modest enhancement factor is obtained, as expected for very short distance between RhB and the metal surface. Given the very thin metal-fluorophore separation, estimated from the size of the D-gluconic acid, the energy transfer or fluorescence quenching is still efficient and the SEF enhancement is just overcoming the energy transfer. Therefore, both SEF and SERRS are observed. Notably, the aggregation of coated nanoparticles also increases the enhancement factor for SEF.

The tetrasaccharide of 1 → 4 β-D-mannopyranuronate (MM) and the alternating tetrasaccharide of 1 → 4b -Dmannopyranuronate and 1 → 4 α-L-gulopyranuronate (MG) were analyzed based on density functional theory (DFT) by employing the Gaussian 03 W package. The molecular geometries were fully optimized by using the Becke’s three-parameter hybrid exchange functional combined with Lee – Yang – Parr correlation functional (B3LYP) and using a 6-31G(d,p) basis set. The calculated IR spectrum of MM presents a band at 1093 cm −1 for C – C stretching vibration, which is in good agreement with the experimental observation (1096 cm −1 ) for the polymannuronate fraction obtained by partial hydrolysis of sodium alginate extracted from the hybrid brown seaweed Lessonia–Macrocystis. The calculated value at 826 cm −1 for MM is in close agreement with the experimental value and confirms that this band is characteristic of polymannuronate blocks. Most of the bands in the IR spectrum are also present in the observed Raman spectrum of the polymannuronate fraction. The experimental IR spectrum of heteropolymeric fraction obtained by partial hydrolysis of sodium alginate shows absorbances similar to those calculated for the model tetrasaccharide (MG). Surface-enhanced Raman scattering (SERS) allows differentiation between the homopolymeric and heteropolymeric fractions of sodium alginate. The SERS spectrum of the heteropolymeric fraction shows an enhanced signal at 731 cm −1 which is present in the calculated Raman spectrum of the tetrasaccharide MG at 729 cm −1 . This band is assigned to the ring-breathing deformation of the β-D-mannopyranuronate and α-L-gulopyranuronate residues. Copyright c � 2010 John Wiley & Sons, Ltd.

The vibrational spectra and surface-enhanced Raman scattering (SERS) of 1,6-diphenyl-1,3,5-hexatriene (DPH) are discussed. The fundamental vibrational frequencies, overtones, and combinations observed in the infrared and Raman spectra of DPH are reported. The interpretation of the observed vibrational spectra was supported by a complete geometry optimization, followed by vibrational frequency and intensity computations for the cis- and trans- isomers of the DPH using density functional theory at the B3LYP/6-31G(d,p) level of theory. Because the molecule is photo-chemically active on Ag metal surfaces, the best SERS results for silver islands were obtained at low temperature and low energy density of the exciting laser line. DPH SERS on Au films was obtained at room temperature.

The photoelectrocatalytic reduction of CO2 on ITO-modified electrodes, with electrostatic assemblies (polycations/quantum dots) (polycations = poly diallyldimethylammonium, PDDA, and poly(2-trimethylammonium)ethyl methacrylate, PMAEMA)), is described in the present work. Nanoparticles of CdTe (5.6 nm) were incorporated through an electric field directed layer-by-layer assembly method on ITO electrodes. Modified surfaces were active toward the reduction of CO2 at −400 mV vs Ag/AgCl; the activity of ITO-(PMAEMA/QDs)6 electrodes was enhanced by 300 mV under irradiation conditions. The photoelectrocatalytic effect was associated with the structure of the polycation and its influence in the assembly. Reaction products at −450 mV were H2, CO, CH3OH, and HCOH.

This article presents the fabrication and characterization of polyisoprene fluorescent films doped with CdTe quantum dots (QDs). The biopolymer (polyisoprene) is extracted from natural rubber latex, generating flexible and transparent films in visible range (transmittance over 90%) ideal as a matrix to support QDs. The water solubility of the biopolymer facilitates its doping with water dispersed QDs at room temperature to obtain the fluorescent films. Thermogravimetric analysis reveals that QDs have no significant effect on the thermal properties of the biopolymer. Photophysical characterization of the solution and solid state (films) of the QDs evidenced that the polymer matrix does not influence its emission properties, the maximum fluorescence peaks have only 2 nm of difference between the solution and solid state (films) samples. Therefore, polyisoprene from natural rubber can be considered as an excellent flexible matrix to fabricate fluorescent films with QDs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45459.

The surface characterization of CdTe QDs synthesized by a novel procedure using glutathione (GSH), low temperatures (60-90 °C) and K 2TeO3 as the -Te precursor is reported. Fluorescence of the produced QDs is stable in the pH range 6-13 and QDs inside eukaryotic cells are highly fluorescent. The surface composition of GSH-CdTe QDs with different spectroscopic properties and particle size distributions was determined by XPS. The XPS analysis indicated that the QDs are essentially CdTe, although all nanoparticles contain 12-24% of CdO (and in one case also TeO2). GSH decomposes with reaction time releasing small amounts of S-2 ions that react with Cd(Te) to yield Cd(Te)S in a smaller amount than that of CdTe. Finally, the use of QDs in fluorescence mediated immunodetection of bacterial pathogens has been evaluated. © 2013 Elsevier B.V. All rights reserved.

CdTe quantum dots (QDs) capped with two relevant biological thiols, glutathione (GSH) or cysteine (Cys) were synthesized in aqueous solution using CdCl2, K2TeO3 and NaBH4 and their chemical, spectroscopic and biocompatibility properties were assessed. Synthesized nanoparticles (NPs) are 3–6 nm in diameter, with emission spectra between 480–580 nm depending on QDs size, and emission quantum yields between 0.35–0.65. The toxicity of thiol-capped CdTe NPs to different bacterial strains was determined. Increased biocompatibility for Cys-capped QDs was observed. In addition, QDs uptake by eukaryotic cells was evaluated by fluorescence microscopy. CdTe-GSH NPs were incorporated into MKN45 cells only in the presence of lipofectamine. On the other hand, although CdTe-Cys NPs were freely incorporated into these cells, the amount of incorporation as well as the number of fluorescent cells was lower than that observed with GSH-capped QDs. Finally, no significant changes in cell morphology as a consequence of GSHor Cys-capped QDs incorporation were observed. Summarizing, our results indicate that the as-synthesized GSHand Cys-capped QDs display differential spectroscopic properties and cellular interactions, being CdTe-Cys more biocompatible than CdTe-GSH NPs.

The vast application of fluorescent semiconductor nanoparticles (NPs) or quantum dots (QDs) has prompted the development of new, cheap and safer methods that allow generating QDs with improved biocompatibility. In this context, green or biological QDs production represents a still unexplored area. This work reports the intracellular CdTe QDs biosynthesis in bacteria. Escherichia coli overexpressing the gshA gene, involved in glutathione (GSH) biosynthesis, was used to produce CdTe QDs. Cells exhibited higher reduced thiols, GSH and Cd/Te contents that allow generating fluorescent intracellular NP-like structures when exposed to CdCl(2) and K(2)TeO(3). Fluorescence microscopy revealed that QDs-producing cells accumulate defined structures of various colors, suggesting the production of differently-sized NPs. Purified fluorescent NPs exhibited structural and spectroscopic properties characteristic of CdTe QDs, as size and absorption/emission spectra. Elemental analysis confirmed that biosynthesized QDs were formed by Cd and Te with Cd/Te ratios expected for CdTe QDs. Finally, fluorescent properties of QDs-producing cells, such as color and intensity, were improved by temperature control and the use of reducing buffers.

Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl2, K2TeO3 and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods. CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd+2 and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, “greener” methods to synthesize cadmium-containing QDs.

This work describes the formation of modified electrodes layer-by-layer assembly of a μ-{meso-5,10,15,20-tetra(pyridyl)porphyrin}tetrakis{bis(bipyridine)chloride ruthenium(II)} coordinated with Zn(II) and Mn(III) in its central cavity and an anionic polyoxotungstate [SiW12O40]4−. The bilayer formation was monitored using electrochemical and UV–vis techniques, following the oxidation process of the RuIII/II couple and the absorbance of the Soret band of porphyrin complexes respectively. It was possible to form 10 stable bilayers onto ITO surface. SEM studies were carried out finding that the morphology of the film depends on the metal center in the porphyrin. The thickness of these films was estimated as 0.603 μm for [Zn(II)TRP]4+/[SiW12O40]4− and 2.18 μm for [Mn(III)TRP]5+/[SiW12O40]4− modified electrodes respectively. Raman spectroscopy showed that new bands appeared for [Mn(III)TRP]5+/[SiW12O40]4− assembly confirming stronger interactions than only electrostatic forces. Kinetics parameters such as charge transfer coefficient, α, and heterogeneous electron transfer rate constant, ks were obtained for both electrodes. Using electrochemical and UV–vis data it was possible to estimate the energy levels involved in the charge transfer process through the films formed. Sensor properties of [Zn(II)TRP]4+/[SiW12O40]4− modified electrode toward chlorite oxidation was tested. The results show electrocatalytic activity, amperometric determination demonstrate a detection limit of 13.8 μM.

The O-antigen determines the specificity of bacterial serotype, a sort of bacterial fingerprinting. In this work we report the extraction, purification and characterization of the O-antigen of two pathogenic bacteria, Escherichia coli O16 and Salmonella typhimurium. Molecular fingerprints found in the vibrational spectra represent a powerful analytical technique for identification (or differentiation) of molecular moieties in complex systems such as pathogens. In addition, advantages of vibrational Raman scattering are unique thanks to the high sensitivity and specificity achieved via surface-enhanced Raman scattering (SERS). SERS is used here to take advantage of characteristic vibrational frequency differences of O-antigens, thus allowing bacterial differentiation. Characteristic fundamental vibrational modes associated with the monosaccharide N-acetylglucosamine and deformations of the O-antigen chains provide the main spectroscopic differences between the O-antigens of E. coli O16 and S.typhimurium.

The surface-enhanced Raman scattering (SERS) of sodium alginates and their hetero- and homopolymeric fractions obtained from four seaweeds of the Chilean coast was studied. Alginic acid is a copolymer of β-D-mannuronic acid (M) and α-L guluronic acid (G), linked 1 → 4, forming two homopolymeric fractions (MM and GG) and a heteropolymeric fraction (MG). The SERS spectra were registered on silver colloid with the 632.8 nm line of a He – Ne laser. The SERS spectra of sodium alginate and the polyguluronate fraction present various carboxylate bands which are probably due to the coexistence of different molecular conformations. SERS allows to differentiate the hetero- and homopolymeric fractions of alginic acid by characteristic bands. In the fingerprint region, all the poly-D-mannuronate samples present a band around 946 cm −1 assigned to C – O stretching, and C –C–H and C –O–H deformation vibrations, a band at 863 cm −1 assigned to deformation vibration of β-C1 –H group, and one at 799 – 788 cm −1 due to the contributions of various vibration modes. Poly-L-guluronate spectra show three characteristic bands, at 928 – 913 cm −1 assigned to symmetric stretching vibration of C – O – C group, at 890 – 889 cm −1 due to C –C–H , skeletal C – C, and C – O vibrations, and at 797 cm −1 assigned to α C1 – H deformation vibration. The heteropolymeric fractions present two characteristic bands in the region with the more important one being an intense band at 730 cm −1 due to ring breathing vibration mode. Copyright c � 2009 John Wiley & Sons, Ltd.