Rodrigo Petoral

Polyethylene glycol-covered ultra-small Gd2O3 nanoparticles for positive contrast at 1.5 T magnetic resonance clinical scanning

The size distribution and magnetic properties of ultra-small gadolinium oxide crystals (US-Gd2O3) were studied, and the impact of polyethylene glycol capping on the relaxivity constants (r1, r2) an ...

Surface functionalization and biomedical applications based on SiC

The search for materials and systems, capable of operating long term under physiological conditions, has been a strategy for many research groups during the past years. Silicon carbide (SiC) is a material, which can meet the demands due to its high biocompatibility, high inertness to biological tissues and to aggressive environment, and the possibility to make all types of electronic devices.This paper reviews progress in biomedical and biosensor related research on SiC. For example, less biofouling and platelet aggregation when exposed to blood is taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices.

Organosilane-functionalized wide band gap semiconductor surfaces

Surface functionalization of wide band gap semiconductors, SiC, ZnO, and GaN, with organosilane is reported. Formation of self-assembled monolayers of mercaptopropyltrimethoxysilane is confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The molecules are adsorbed on the surfaces through the silane groups with the free thiol groups molecularly oriented away from the surface. Moreover, chemisorption via the thiolate is observed for the ZnO surface. Immobilization of a model biomolecule to the functionalized surface is demonstrated. An amino acid derivative, i.e., phosphotyrosine derived thiol, is linked on the functionalized ZnO and GaN surfaces via formation of disulfide bridges.Surface functionalization of wide band gap semiconductors, SiC, ZnO, and GaN, with organosilane is reported. Formation of self-assembled monolayers of mercaptopropyltrimethoxysilane is confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The molecules are adsorbed on the surfaces through the silane groups with the free thiol groups molecularly oriented away from the surface. Moreover, chemisorption via the thiolate is observed for the ZnO surface. Immobilization of a model biomolecule to the functionalized surface is demonstrated. An amino acid derivative, i.e., phosphotyrosine derived thiol, is linked on the functionalized ZnO and GaN surfaces via formation of disulfide bridges.

XPS and NEXAFS study of tyrosine-terminated propanethiol assembled on gold

Tyrosine-terminated propanethiol (TPT), tyrosine linked to 3-mercaptopropionic acid through an amide bond, is adsorbed to gold surfaces. The adsorbates are characterized by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). XPS is used to investigate the chemical binding and electronic structure of the monolayer. Strong molecular binding of the tyrosine derivative on the gold surface through the sulfur atom is attained. Angle-dependent XPS results shows that TPT molecules are oriented with the sulfur atoms molecularly oriented close to the gold surface and that the phenol moiety is oriented away from the gold surface. Average orientation of the adsorbate on gold is deduced using the NEXAFS results. It shows that the main molecular axis is tilted approximately 38° relative to the Au surface normal. The ring plane of the phenol moiety exhibits a preferential orientation with an average tilt angle of the normal of the ring plane from the surface normal of about 60°.

Arg-Cys and Arg-cysteamine adsorbed on gold and the G-protein-adsorbate interaction

The dipeptide, Arg–Cys, and the related molecule, Arg–cysteamine, are adsorbed to gold surfaces and the monolayers are characterized. Chemical binding and electronic structure of the monolayers are obtained by X-ray photoelectron spectroscopy (XPS). Strong molecular binding of the adsorbates to gold surface through the sulfur atom is attained. Orientation of the adsorbates on gold is studied using infrared reflection absorption spectroscopy (IRAS). Arg–Cys is interpreted to be adsorbed on gold in a compact configuration. The Arg–cysteamine molecule is adsorbed on gold with the main molecular axis perpendicular to the surface. Interaction of G-protein with the adsorbates was studied using the surface plasmon resonance (SPR) technique. It is believed that arginine has a major role in G-protein recognition since the G-protein-coupled receptor (GPCR) α2A has an arginine-rich region in the G-protein-binding part of the third intracellular loop.

Surface engineering of functional materials for biosensors

Single crystal SiC with suitable surface termination and ZnO films on top have been grown. Biomolecular immobilization on the grown surfaces has been performed. APTES on Si terminated SiC surfaces and reaction with a compound containing a pre-activated carboxylic group was used. The rate of success for surface functionalization was monitored by XPS. A successful two-step functionalization including binding of MPA through an amide bond formation, between the amine group of APTES and the carboxylic group in MPA on ZnO epilayers, was shown as a proof of concept for biofunctionalization

Synthesis of tetrathiafulvalenes suitable for self-assembly applications

A series of new tetrathiafulvalenes, with double alkylthiol or alkyldisulfide substitution, have been prepared with a synthetic procedure that allows variation of different substituents. The target compounds 6a–e and 15e–i are sparsely soluble in organic solvents, but TTFs 6d and 15g gave a relatively dense packed monolayer upon exposure to gold surfaces.

Surface Functionalization of SiC for Biosensor Applications

SiC is a biocompatible material and a candidate as a transducer for biosensors. Here we have investigated the possibility to functionalize SiC with biomolecules. We have also processed very simple devices and performed electrical characterization. Double polished SiC samples with a C-face substrate and Si-face low doped epilayer have been functionalized on both sides. The SiC was first treated by HF in order to remove the native oxide, partly successful on the Si-face side but probably not on the C-face side. MPTMS, 3-mercaptopropyl trimethoxysilane, was chosen as the biomolecule since it has both a silanol group to be used as an anchoring group to the substrate and a thiol group available for further linking possibilities. The functionalization was evaluated by XPS, contact angle experiments, AFM and electrical measurements. The MPTMS molecules attached with the thiol (or sulphur containing) group pointing out from the surface on both faces of the SiC. Interesting differences between the two faces are however revealed by the analysis.

Ground state and phase transitions in a system of arg-cysteamines self-assembled on a Au(111) crystal surface

The translational and orientation order of arg-cysteamine molecules chemiabsorbed on the Au(111) crystal surface is considered. Couplings between carbon, nitrogen, and hydrogen atoms of the n-alkanethiols are approximated by the Lennard-Jones potential. Moreover, hydrogen bonds between oxygen and nitrogen and dipole-dipole interactions of the dipole moments of different atomic groups are taken into account. It is found that molecules are arranged in a 2 x 2 lattice and have the total symmetry C6 x Z2. The critical temperature of the phase transition to the tilted state Tc1, which breaks the symmetry C6, is estimated to be extremely high. The spontaneous breakdown of the remaining symmetry Z2 leads to the twisted state of the molecules and has the critical temperature Tc2=340 K.