Javier Hernández-Paredes

Hollow Au–Ag bimetallic nanoparticles with high photothermal stability

Noble metal nanoparticles have received much attention due to their interesting properties that make them useful in different technical fields. Metallic nanoparticles with optical properties in the near infrared region of the electromagnetic spectrum are of great importance for biological applications, in particular photothermal therapy, as it is greatly enhanced by metallic nanoparticles. However, despite the large amount of work that has been done with metallic nanoparticles for thermal therapy, there is a reduced amount of scientific reports about the photothermal stability of most studied nanoparticles. In this work, hollow Au–Ag bimetallic nanoparticles were synthesized via galvanic replacement reaction, with optical properties that can be tuned systematically along the visible and near infrared region of the spectrum, by changing the pH before the synthesis of the templates and by controlling the amount of gold added for the synthesis of the nanoshells. The synthesized nanoparticles exhibit good photothermal properties when illuminated with an 808 nm laser light. An increase of temperature of nearly 20 °C is achieved after 15 minutes of irradiation. Moreover, the Au–Ag nanoparticles show good reusability even after ten heating/cooling cycles. The nanoparticles also retain their optical properties after 12 hours of continuous irradiation and are able to maintain their photothermal characteristics of increasing the temperature at the same levels during the entire process.

Experimental and theoretical investigation on the molecular structure, spectroscopic and electric properties of 2,4-dinitrodiphenylamine, 2-nitro-4-(trifluoromethyl)aniline and 4-bromo-2-nitroaniline

2,4-Dinitrodiphenylamine (I), 2-nitro-4-(trifluoromethyl)aniline (II) and 4-bromo-2-nitroaniline (III) have been investigated by DFT and experimental FTIR, Raman and UV-Vis spectroscopies. The gas-phase molecular geometries were consistent with similar compounds already reported in the literature. From the vibrational analysis, the main functional groups were identified and their absorption bands were assigned. Some differences were found between the calculated and the experimental UV-Vis spectra. These differences were analyzed and explained in terms of the TD-DFT/B3LYP limitations, which were mainly attributed to charge-transfer (CT) effects. These findings were in agreement with previous works, which reported that TD-DFT/B3LYP calculations diverge from experimental results when the electronic transitions involve CT. Despite this, TD-DFT/B3LYP calculations provided satisfactory results and a detailed description of the electronic transitions involved in the absorption bands of the UV-Vis spectra. In terms of the NLO properties, it was found that compound (I) is a good candidate for NLO applications and deserves further study due to its good β values. However, the β values for compounds (II) and (III) were negatively affected compared to those found on o-nitroaniline.

Photo-mediated Seedless Synthesis of Silver Nanoparticles Using CW-Laser and Sunlight Irradiation

Noble metal nanoparticles, such as silver nanoparticles (AgNPs), have found technological applications due to their localized surface plasmon resonance (LSPR). In this context, a great quantity of synthetic methods for the preparation of AgNPs have been developed, including photo-chemical synthesis [1]. The photo-chemical synthesis is an advantageous technique because it is simple and environmentally friendly [2]. In this work, synthesis of AgNPs was performed via direct photo-reduction process of the silver nitrate and sodium citrate solutions without the previous addition of silver seeds.

Comparison of spatially and temporally resolved diffuse transillumination measurement systems for extraction of optical properties of scattering media.

This paper discusses the main differences between two different methods for determining the optical properties of tissue optical phantoms by fitting the spatial and temporal intensity distribution functions to the diffusion approximation theory. The consistency in the values of the optical properties is verified by changing the width of the recipient containing the turbid medium; as the optical properties are an intrinsic value of the scattering medium, independently of the recipient width, the stability in these values for different widths implies a better measurement system for the acquisition of the optical properties. It is shown that the temporal fitting method presents higher stability than the spatial fitting method; this is probably due to the addition of the time of flight parameter into the diffusion theory.

Characterization of the Molecular Crystal L-Alaninium Oxalate by Raman Microscopy, Optical Microscopy and X-ray Powder Diffraction

There are studies that claim that molecular materials formed by combination of amino acids with other organic or inorganic compounds exhibit good NLO properties, low laser damage threshold and acceptable mechanical and thermal properties [2]. For example, oxalates of amino acids have displayed good NLO properties and efficient second harmonic generation (SHG). In particular, L-alaninium oxalate (LAO) is a molecular crystal with formula C3H8NO2 ·C2HO4 , that has attracted attention due to its good NLO performance [3]. For the present work we carried out a structural characterization of the multi-component molecular complex LAO, which has been synthetized by the slow evaporation technique and mechanochemical route.

Study of Alkali Halide Solid Solutions by Scanning Electron Microscopy and X-ray Diffraction

Alkali halide materials are ionic crystals with the chemical formula MX, where M is an alkali metal (Li, Na, K, Rb, Cs) and X is a halogen (F, Cl, Br, I). They can form solid solutions by substitution between the alkali metals, the halogens or both [1]. Solid solutions are widely studied with the aim to understand the phase selection during solidification. The objective of the present work is to determine the phases present in the final microstructure of a crystalline material obtained from the melt of various alkali halide salts.

Absolute Configuration, Optical Activity and Raman Microscopy of L and D-Glutamic Acid

1. Laboratorio de Estructura Biomolecular, Centro de Investigación en Alimentación, y Desarrollo, A.C., Carretera a Ejido La Victoria km 0.6 s/n, Hermosillo, Sonora, C.P. 83304, México. 2. Departamento de Ingeniería Celular y Biocatálisis. Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Cuernavaca, Morelos, 62210, México. 3. Posgrado en Nanotecnología, Departamento de Física, Universidad de Sonora (UNISON), Edificio 3R, Blvd. Luis Encinas J. y Rosales s/n Col. Centro, Hermosillo, Sonora, C.P. 83000, México.

Study of the phase equilibria in the L-alanine - sodium nitrate system by optical microscopy and X-ray powder diffraction

There is a continuous interest on controlling the final crystalline form of molecular materials. Among the organic materials, amino acids are of particular interest since they have relevant implications for biological systems [1]. In addition, they can form semi-organic (hybrid) materials in combination with inorganic salts [2,3]. A key to optimizing their physical and chemical properties is to control their final crystalline form.