Alejandro Torres-Castro

Glucose detection using SERS with multi-branched gold nanostructures in aqueous medium

Gold nanoparticles (AuNPs), multi-branched gold nanoparticles (MBGNs), and silica-coated MBGNs (MBGNs-silica) were studied for rhodamine B (RB) and α-glucose detection at low concentration. The MBGNs SPR band in the NIR, which is tunable, is useful for SERS that was demonstrated using rhodamine B and α-glucose as probe molecules with detection limits of 50 pM and 5 mM (90 mg dL−1), respectively, much lower than that using regular AuNPs. The SERS signals of RB and α-glucose using MBGNs-silica are further enhanced with respect to AuNPs and MBGNs, which is attributed to the aggregation of the MBGNs and a stronger interaction. In the case of α-glucose, the functionalization process performed to both, α-glucose molecules and MBGNs, improves the interaction and allows measurements at low concentration.

Totally Ecofriendly Synthesis of Silver Nanoparticles from Aqueous Dissolutions of Polysaccharides

In this contribution, a totally ecofriendly synthesis of silver nanoparticles from aqueous dissolution of polysaccharides is reported. The synthesis of nanoparticles was performed using aqueous dissolutions of silver nitrate (AgNO3) and carboxymethyl-cellulose (CMC) as both reducing and stabilization agent and using different AgNO3 : CMC weight ratios. Resultant yellowish to reddish dispersions were characterized by means of transmission electron microscopy and their related techniques, such as bright field and Z-contrast imaging and electron diffraction, as well as ultraviolet-visible and infrared spectroscopic techniques. The experimental evidence suggests that the morphology and particle size distribution of the silver nanoparticles depend on the AgNO3 : CMC weight ratio. This feature seems to be related to the stabilization given by the CMC matrix, which, according to our experimental findings, is steric in nature. Regarding such experimental evidence, a synthesis mechanism in which CMC acts as stabilizer and reducing agent is proposed.

Iron Oxide Nanoparticles Obtained from a Fe(II) - Chitosan Polymer Film

In this work, iron oxide nanoparticles (~5 nm) embedded in a chitosan polymer film, were synthesized. In order to obtain this nanostructured material, firstly a homogenous film of Fe(II)-chitosan was prepared. The resulting composite film has a thickness of ~140μm. Iron oxide nanoparticles were in-situ synthesized by treating the composite film with H2O2 under alkaline conditions. The morphological analysis by Transmission Electron Microscopy (TEM) shows the nanoparticles were embedded and stabilized in chitosan polymer film. The magnetic behavior was studied by magnetization measurements. The magnetization curves at room temperature showed that iron oxide nanoparticles have a superparamagnetic behavior.

Effect of TEA on the blue emission of ZnO quantum dots with high quantum yield

This work reports the luminescence, morphology and synthesis of ZnO quantum dots using a simple wet chemical method and different concentrations of Triethanolamine (TEA) as surfactant. Those nanoparticles emitted a strong blue emission band centered at 429 nm when they are dispersed in hexane. Spherical quantum dots with sizes ranging from 3 to 7 nm were obtained for concentrations from 0 to 0.7 ml. of TEA, whereas a mixture with oval-like nanoparticles was observed from concentrations above of 1.1 ml of TEA. It was also possible to control the values of the band gap in ZnO quantum dots depending on the content of TEA. Based on the high quantum yield of 81% measured for those ZnO nanoparticles respect to quinine sulfate dye (QS), it is suggested that such nanoparticles could be used for biolabeling and ZnO based LEDs.

Ni Nanoparticles Elaborated with an Ar Ion Polishing Technique

Ni nanoparticles where obtained from a Ni sample milled with Ar ions by using a Gatan precision ion polishing system, normally used for Transmission Electron Microscopy (TEM) sample preparation. Deposition of Ni nanoparticles was performed over two different surfaces: on a double sided carbon tape and, on a Cu grid covered with collodion film. A continuos film of Ni was characterized, over the carbon tape by SEM and EDAX techniques. The last surface was analyzed by TEM. In both cases, a thin film composed of Ni nanoparticles, was founded and result obtained by TEM, show a nanoparticle diameter of about 4 nm.

Synthesis, characterization and surface enhanced Raman scattering of hollow gold-silica double shell nanostructures

Hollow gold-silica double-shell (HGSDS) and hollow gold-silica composite (HGSC) nanostructures have been synthesized and their structural, optical, and surface-enhanced Raman scattering (SERS) properties have been characterized. The structure of the HGSDS and HGSC was determined by scanning transmission electron microscopy (STEM) and high- resolution transmission electron microscopy (HRTEM). STEM images of the HGSDS reveal a reasonably uniform diameter of approximately 500-1000 nm with SiO2 deposited, using a modified Stober method, onto aggregated structures of hollow gold nanospheres (HGNs). The HGSC structures were determined to be 30 nm in size by HRTEM. The broad surface plasmon resonance (SPR) absorption of both the HGSDS and HGSC structures is dominated by gold but concomitantly influenced by the silica, with the peak position blue-shifted by ∼100 nm relative to that of the starting HGNs. The broad and tunable SPR band can be useful for applications such as SERS. As a preliminary demonstration, SERS studies of Rhodamine 6G (R6G) and β-glucose have been carried out. The results show reproducible detection with limits as low as 0.9 and 5 mM, respectively. Glucose has traditionally been difficult to detect with SERS due to its small Raman cross-section and low SERS signal arising from weak interaction with the metal substrate. Compared to HGNs, the SERS signal of β-glucose using HGSDS and HGSC is enhanced, which is attributed to the relatively strong interaction between the glucose and the SiO2 surface. These results demonstrate that the silica-modified HGN structures are both interesting and useful as a result of their unique structural and optical properties.

Chemical Characterization of DC-Sputtered In2O3 Films with a Top SnO2 Layer

In2O3 thin films with a top layer of SnO2 were deposited onto glass substrates by DC reactive-magnetron sputtering. After deposition, In2O3/SnO2 samples were annealed in vacuum at 400oC. Structural, optical, and chemical composition was investigated by X-ray diffraction, UV-Vis spectroscopy and XPS, respectively. X-ray data showed that films grow polycrystalline, where indium oxide crystallized in cubic as the main phase, with a preferential growth at the [0002] direction and lattice parameter of 10.11 Å. Signals of rhombohedral phase were also detected. XPS depth profiles show that tin coexists in Sn2+ and Sn4+, while indium maintains the In2O3 stoichiometry. Binding energy of Sn4+ bound to oxygen was detected at 468 eV while In2+ bound to oxygen at 444.7 eV. Nor tertiary compounds were detected at the In2O3/SnO2 interface, neither In or Sn in metallic state.

Wet chemical synthesis of quantum dots for medical applications

In recent years the use of nanoparticles in medical applications has boomed. This is because the various applications that provide these materials like drug delivery, cancer cell diagnostics and therapeutics [1-5]. Biomedical applications of Quantum Dots (QDs) are focused on molecular imaging and biological sensing due to its optical properties. The size of QDs can be continuously tuned from 2 to 10 nm in diameter, which, after polymer encapsulation, generally increases to 5 – 20 nm diminishing the toxicity. The QDs prepared in our lab have a diameter between 2 to 7 nm. Particles smaller than 5 nm can interact with the cells [2]. Some of the characteristics that distinguish QDs from the commonly used fluorophores are wider range of emission, narrow and more sharply defined emission peak, brighter emission and a higher signal to noise ratio compared with organic dyes [6]. In this paper we will show our progress in the study of the interaction of quantum dots in live cells for image and Raman spectroscopy applications. We will also show the results of the interaction of quantum dots with genomic DNA for diagnostic purposes.

Synthesis of Transparent Conductive Thin Films of In2O3 and SnO2 by DC Magnetron Sputtering

Study of optical and microestructural properties in In2O3 and SnO2 multilayer thin films synthesis by DC magnetron sputtering characterized with SEM, X-RD and four point probe resistivity where is possible appreciate an enhancement in conductivity.