Alberto Hernández Creus

Quinone-rich poly(dopamine) magnetic nanoparticles for biosensor applications.

Novel core-shell quinone-rich poly(dopamine)-magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier-transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer-film thickness of 2 nm. The core-shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA M(-1)  cm(-2) , a low limit of detection (0.02 mM), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer.

Nanocrystals distribution inside the writing lines in a glass matrix using Argon laser irradiation

Localized modification in strontium barium niobate glass doped with Ho(3+) under laser irradiation has been carried out. The preliminary samples of this study have been fabricated by the melt quenching method and doped with 2.5% mol of Ho(3+). A 3.5W cw multiline Ar-laser has been focused and shifted in a line during laser irradiation. The formation of Strontium Barium Niobate nanocrystals has been confirmed by X-ray diffraction, atomic force microscope image and fluorescence. They have been localized in the irradiation line and change the optical properties of the sample. These nanocrystals have been obtained due to the excitation of the Ho(3+) ions which under nonradiative processes produced the heating of the sample. In this work, it has been demonstrated that the diffusion of the Nb(5+) ions to the border of the irradiated line controls the growth of the nanocrystals in the sample.

New findings for the composition and structure of Ni nanoparticles protected with organomercaptan molecules.

Here we explore the synthesis of alkanethiol-coated Ni NPs following the one-phase reaction method by Brust et al. The reduction of NiCl2 with NaBH4 in the presence of dodecanethiol (C12SH) yields a complex product that is difficult to identify as illustrated in the figure of merit. We synthesized Ni(II) dodecanethiolate (C12S) (without the addition of NaBH4) for comparison and performed an exhaustive characterization with TEM, HR-TEM, AFM, MFM, XPS, XRD, UV-vis, magnetism, and FT-IR. It is found that the organic coating is not quite a well-organized self-assembled monolayer (SAM) surrounding the Ni cluster as previously reported. XPS and XRD data show slight differences between both syntheses; however, Ni(II) thiolate appears to be more stable than reduced Ni when exposed to ambient air, indicating the propensity of metallic Ni to oxidize. It has been shown that irradiating with TEM electrons over various metal thiolates leads to nanoparticle formation. We irradiated over Ni(II) thiolate and observed no evidence of NP formation whereas irradiating a reduced Ni sample exhibited an ~3.0 nm nanoparticle diameter. Magnetism studies showed a difference between both samples, indicating ferromagnetic character for the reduced Ni sample. According to our results, the product of the synthesis is comprised of ultrasmall metallic clusters embedded in some form of Ni(II) C12S. In this work, we open a discussion of the chemical nature of the core and the shell in the synthesis of Ni NPs protected with organomercaptan molecules.

Effect of alumina content and heat treatment on microstructure and upconversion emission of Er3＋ ions in oxyfluoride glass-ceramics

Abstract The effect of alumina content and heat treatment temperature and time, on microstructure and Er3+ (0.5 mol.%) emission of oxyfluoride glass-ceramics were investigated in this research. Two values of 1.8 (SA1.8Er0.5) and 2.18 (SA2.18Er0.5) were selected in this research for SiO2/Al2O3 ratio. According to DTA results, precursor glasses were heat treated at 630, 660 and 690 °C for 4 h and some glasses were also heat treated at 630 °C for 48 and 72 h. The results indicated that alumina content had significant effect on phase separation and viscosity of the glasses. Therefore the size, size distribution, and volume concentration of nano CaF2 crystals which precipitated during the heat treatment depended on alumina content of the glass. Due to the much smaller size of the precipitated CaF2 crystals in the glasses of low alumina content, these samples maintained excellent transparency and had narrower crystal size distribution than the high alumina glasses. The crystal size was increased markedly with the temperature increasing from 630 to 690 °C. On the other hand a slight increase was observed in the crystal size by raising the heat treatment time in both glasses. Results indicated that in low alumina content glass (SA2.18Er0.5) the size of CaF2 nanocrystals was controlled in one order of magnitude. The increase of heat treatment time and temperature led to the incorporation of Er3+ ions into CaF2 crystalline phase, increasing significantly the upconversion intensity. After heat treatment at 690 °C for 4 h, atomic force microscope (AFM) revealed the development of small crystals with an average size of 80 and 30 nm in SA1.8Er0.5 and SA2.18Er0.5 samples, respectively.

Self-assembly of flagellin on Au(111) surfaces.

The adsorption of flagellin monomers from Pseudomonas fluorescens on Au(111) has been studied by Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Surface Plasmon Resonance (SPR), and electrochemical techniques. Results show that flagellin monomers spontaneously self-assemble forming a monolayer thick protein film bounded to the Au surface by the more hydrophobic subunit and exposed to the environment the hydrophilic subunit. The films are conductive and allow allocation of electrochemically active cytochrome C. The self-assembled films could be used as biological platforms to build 3D complex molecular structures on planar metal surfaces and to functionalize metal nanoparticles.

Mapping nanometric electronic property changes induced by an aryl diazonium sub-monolayer on HOPG

The morphology as well as the electric and electronic properties of aryl diazonium, in particular 4-nitrobenzene-diazonium (NBD), films on HOPG surfaces have been studied at the nanoscale level. By controlling the 2,2-diphenyl-1-picrylhydrazyl concentration during the NBD film growth, we have been able to control the thickness of the layer. The implications of NBD submonolayer adsorption on the electrical properties of this system have been analysed through Density Functional Theory (DFT) calculations, Atomic Force (AFM), Electric Force (EFM) and Kelvin Probe Force (KPFM) microscopies. DFT simulations showed that the NBD molecule adsorbs almost perpendicularly to the HOPG surface, which was confirmed experimentally through AFM imaging in the dynamic mode. In addition, DFT calculations showed that the adsorbed NBD has an appreciable dipole moment directed towards the HOPG surface and along the vertical direction of the HOPG surface. The existence of this dipole is the origin of the EFM contrast observed between the NBD-free and NBD-covered regions when a bias of -2 V was applied to the tip. Besides, the KPFM measurements show that the NBD adsorption leads to higher work function values, which is in agreement with the DFT calculations. Noticeably, our studies show that the KPFM signal is sensitive to the partial NBD coverage of the HOPG surface below the monolayer level.

The Role of a Double Molecular Anchor on the Mobility and Self‐Assembly of Thiols on Au(111): the Case of Mercaptobenzoic Acid

The dynamics of the self-assembly process of thiol molecules on Au(111) is affected by the interplay between molecule-substrate and molecule-molecule interactions. Therefore, it is interesting to explore the effect of a second anchor to the gold surface, in addition to the S atom, on both the order and the feasibility of phase transitions in self-assembled monolayers. To assess the role of an additional O anchor, we have compared the adsorption of two mercaptobenzoic acid isomers, 2-mercaptobenzoic acid (2-MBA) and 4-mercaptobenzoic acid (4-MBA), on Au(111). Results from scanning tunneling microscopy, X-ray photoelectron spectroscopy, electrochemical techniques, and density functional theory calculations show that the additional O anchor in 2-MBA hinders surface mobility, reducing domain size and impeding the molecular reorganization involved in phase transition to denser phases on the Au(111) substrates. This knowledge can help to predict the range order and molecular density of the thiol SAM depending on the chemical structure of the adsorbate.

Microscopy analysis of pyramid formation evolution with ultra-low concentrated Na2CO3/NaHCO3 solution on (100) Si for solar cell application.

An analysis of the nucleation mechanism of pyramids formed in (100) silicon in Na2CO3/NaHCO3 solution has been carried out. This texturization process of silicon by means of Na2CO3/NaHCO3 solutions is of special interest because it can be applied to the silicon solar cell industry to texture solar cell surfaces to decrease the front reflection and enhance light trapping in the cells. For this purpose, two microscopy techniques-scanning electron microscopy and atomic force microscopy-have been used to study the different stages of pyramidal nucleation and formation. The different aspects and factors involved in the texturization process require different analysis conditions and microscopy resolution. Tracing the transformation of determined surface areas and structures has been achieved, contributing clarification of the mechanism of pyramid nucleation in Na2CO3/NaHCO3 solutions.

Electrochemical Preparation and Delivery of Melanin–Iron Covered Gold Nanoparticles

Attractive combination: Biopolymer-modified nanoparticles which combine magnetic properties with biocompatibility are prepared and delivered following a three-step strategy (see figure): i) Adsorption of thiol-capped metal nanoparticles on graphite, ii) electrochemical modification, iii) potential-induced delivery of the modified nanoparticles to the electrolyte. Thiol-capped gold nanoparticles modified with iron-melanin are attractive because they combine magnetic properties and biocompatibility. The biopolymer modified nanoparticles are prepared and delivered following a three step strategy: i) adsorption of thiol-capped metal nanoparticles on graphite, ii) electrochemical deposition of melanin-iron, iii) potential-induced delivery of the modified nanoparticles to the electrolyte.

Exploring photosensitization as an efficient antifungal method

Lipid bilayers containing ergosterol show signs of destruction when they are treated with singlet oxygen, due to the conversion of ergosterol into its peroxy derivative. Applying this previous knowledge, an antifungal method was explored using Candida tropicalis as model, and membrane permeation under photosensitization conditions became evident. These data were complemented through AFM images of artificial lipid bilayers, using cholesterol or ergosterol as structural sterols, showing their corresponding morphologies at the nanoscale. Based on these results, an antifungal method was developed, which shows evidence of the extent of membrane permeation during photosensitization. Such photosensitization offers an effective alternative treatment, especially in membranes with a high ergosterol content, suggesting that this procedure constitutes an easy and efficient antifungal method.