Influence of bio-coatings on the recording performance of neural electrodes.

Neural probes are complex devices consisting of metallic (often Pt based) electrodes, spread over an insolating/dielectric backbone. Their functionality is often limited in time because of the formation of scaring tissues around the implantation tracks. Functionalization of the probes surface can be used to limit the glial scar reaction. This is however challenging, as this treatment has to be equally efficient on all probe surfaces (metallic as well as dielectric) and should not influence the electrodes performances. This paper presents a novel technique to functionalize recording neural probes with hyaluronic acid (HyA), a major component of the extracellular matrix (ECM). HyA and the probe surface are both modified to make the reaction feasible: HyA is chemically functionalized with SS-pyridine groups while the probe surfaces are silanized. The thiol groups thus introduced on the probe surface can then react with the HyA SS-pyridine group, resulting in a covalent bonding of the latter on the former. The electrodes are protected by introducing a pretreatment step, namely an additional hyaluronic acid layer on the platinum electrode, prior to the silanization process, which was found to be effective in reducing electrode impedance under optimized conditions.

Small Pd nanoparticles supported in large pores of mesocellular foam: an excellent catalyst for racemization of amines.

Highly dispersed palladium nanoparticles (1-2 nm) supported in large-pore mesocellular foam (MCF; 29 nm) were synthesized. The Pd-nanocatalyst/MCF system was characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The performance of the Pd nanocatalyst obtained was examined for amine racemization. The Pd nanocatalyst showed higher activity and selectivity toward racemization of (S)-1-phenylethyl amine than any other amine racemization catalyst reported so far and it could be reused several times. Our data from TEM and XRD suggest a restructuring of the Pd nanocatalyst from amorphous to crystalline and an increase in Pd nanocatalyst size during the racemization reaction. This led to an unexpected increase of activity after the first use. The Pd nanocatalyst obtained can be integrated with other resolving processes of racemic organic compounds to increase the yield of chiral organic products.

Valence-band electronic structure of iron phthalocyanine: an experimental and theoretical photoelectron spectroscopy study.

The electronic structure of iron phthalocyanine (FePc) in the valence region was examined within a joint theoretical-experimental collaboration. Particular emphasis was placed on the determination of the energy position of the Fe 3d levels in proximity of the highest occupied molecular orbital (HOMO). Photoelectron spectroscopy (PES) measurements were performed on FePc in gas phase at several photon energies in the interval between 21 and 150 eV. Significant variations of the relative intensities were observed, indicating a different elemental and atomic orbital composition of the highest lying spectral features. The electronic structure of a single FePc molecule was first computed by quantum chemical calculations by means of density functional theory (DFT). The hybrid Becke 3-parameter, Lee, Yang and Parr (B3LYP) functional and the semilocal 1996 functional of Perdew, Burke and Ernzerhof (PBE) of the generalized gradient approximation (GGA-)type, exchange-correlation functionals were used. The DFT/B3LYP calculations find that the HOMO is a doubly occupied π-type orbital formed by the carbon 2p electrons, and the HOMO-1 is a mixing of carbon 2p and iron 3d electrons. In contrast, the DFT/PBE calculations find an iron 3d contribution in the HOMO. The experimental photoelectron spectra of the valence band taken at different energies were simulated by means of the Gelius model, taking into account the atomic subshell photoionization cross sections. Moreover, calculations of the electronic structure of FePc using the GGA+U method were performed, where the strong correlations of the Fe 3d electronic states were incorporated through the Hubbard model. Through a comparison with our quantum chemical calculations we find that the best agreement with the experimental results is obtained for a U(eff) value of 5 eV.

Performance of a biomimetic oxidation catalyst immobilized on silicon wafers: comparison with its gold congener.

With the aim of extending the usefulness of an existing biomimetic catalytic system, cobalt porphyrin catalytic units with thiol linkers were heterogenized via chemical grafting to silicon wafers and utilized for the catalytic oxidation of hydroquinone to p-benzoquinone. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology and composition of the heterogeneous catalyst. The results of the catalytic oxidation of hydroquinone obtained with porphyrins grafted on silicon were compared with those obtained earlier with the same catalyst in homogeneous phase and immobilized on gold. It was found that the catalysis could run over 400 h, without showing any sign of deactivation. The measured catalytic activity is at least 10 times higher than that measured under homogeneous conditions, but also 10 times lower than that observed with the catalytic unit immobilized on gold. The reasons of this discrepancy are discussed in term of substrate influence and overlayer organization. The silicon-immobilized catalyst has potential as an advanced functional material with applications in oxidative heterogeneous catalysis of organic reactions, as it combines long-term relatively high activity with low cost.

Short and long term biocompatibility of NeuroProbes silicon probes.

Brain implants provide exceptional tools to understand and restore cerebral functions. The utility of these devices depends crucially on their biocompatibility and long term viability. We addressed these points by implanting non-functional, NeuroProbes silicon probes, without or with hyaluronic acid (Hya), dextran (Dex), dexamethasone (DexM), Hya+DexM coating, into rat neocortex. Light and transmission electron microscopy were used to investigate neuronal survival and glial response. The surface of explanted probes was examined in the scanning electron microscope. We show that blood vessel disruption during implantation could induce considerable tissue damage. If, however, probes could be inserted without major bleeding, light microscopical evidence of damage to surrounding neocortical tissue was much reduced. At distances less than 100 microm from the probe track a considerable neuron loss ( approximately 40%) occurred at short survival times, while the neuronal numbers recovered close to control levels at longer survival. Slight gliosis was observed at both short and long term survivals. Electron microscopy showed neuronal cell bodies and synapses close (<10 microm) to the probe track when bleeding could be avoided. The explanted probes were usually partly covered by tissue residue containing cells with different morphology. Our data suggest that NeuroProbes silicon probes are highly biocompatible. If major blood vessel disruption can be avoided, the low neuronal cell loss and gliosis should provide good recording and stimulating results with future functional probes. We found that different bioactive molecule coatings had small differential effects on neural cell numbers and gliosis, with optimal results achieved using the DexM coated probes.

A magnetic microchip for controlled transport of attomole levels of proteins.

A novel method of controlled transport of proteins immobilized on micrometre-sized magnetic beads in a lab-on-a-chip environment is presented. Bead motion is controlled by lithographically made magnetic elements forming transportation lines in combination with an applied in-plane rotating magnetic field. In this way, transport of attomole amounts of proteins is controlled with micrometre precision. Also, the activity of proteins immobilized on the beads is demonstrated by injecting antibodies into the system. A critical step in developing the method was to reduce sticking forces between beads and substrate during transportation of proteins. Charge interaction was found to be of minor importance compared to hydrophobic forces. To achieve a reliable transport of biologically active proteins, both substrate and beads were coated with polyethylene glycol (PEG) and the protein covered beads were suspended in buffer with surfactants. The described system fulfils all the important unit operations of a microfluidic platform and, as a further advantage, presents less need for microchannels and electric wiring.

Effects of Congo red on aß(1-40) fibril formation process and morphology.

Alzheimer's disease (AD), an age-related neurodegenerative disorder, is the most common form of dementia, and the seventh-leading cause of death in the United States. Current treatments offer only symptomatic relief; thus, there is a great need for new treatments with disease-modifying potential. One pathological hallmark of AD is so-called senile plaques, mainly made up of ß-sheet-rich assemblies of 40- or 42-residue amyloid ß-peptides (Aß). Hence, inhibition of Aß aggregation is actively explored as an option to prevent or treat AD. Congo red (CR) has been widely used as a model antiamyloid agent to prevent Aß aggregation. Herein, we report detailed morphological studies on the effect of CR as an antiamyloid agent, by circular dichroism spectroscopy, photo-induced cross-linking reactions, and atomic force microscopy. We also demonstrate the effect of CR on a preaggregated sample of Aß(1-40). Our result suggests that Aß(1-40) follows a different path for aggregation in the presence of CR.

Poly-N-methylated amyloid beta-peptide (Abeta) C-terminal fragments reduce Abeta toxicity in vitro and in Drosophila melanogaster.

Alzheimer's disease (AD), an age related neurodegenerative disorder, threatens to become a major health-economic problem. Assembly of 40- or 42-residue amyloid beta-peptides (Abeta) into neurotoxic oligo-/polymeric beta-sheet structures is an important pathogenic feature in AD, thus, inhibition of this process has been explored to prevent or treat AD. The C-terminal part plays an important role in Abeta aggregation, but most Abeta aggregation inhibitors have targeted the central region around residues 16-23. Herein, we synthesized hexapeptides with varying extents of N-methylation based on residues 32-37 of Abeta, to target its C-terminal region. We measured the peptides' abilities to retard beta-sheet and fibril formation of Abeta and to reduce Abeta neurotoxicity. A penta-N-methylated peptide was more efficient than peptides with 0, 2, or 3 N-methyl groups. This penta-N-methylated peptide moreover increased life span and locomotor activity in Drosophila melanogaster flies overexpressing human Abeta(1-42).

Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite.

Low temperature scanning tunneling microscopy (STM) studies of metal-free phthalocyanine (H2Pc) adsorbed on highly oriented pyrolytic graphite (HOPG) have shown ordered arrangement of molecules for low coverages up to 1 ML. Evaporation of H2Pc onto HOPG and annealing of the sample to 670 K result in a densely packed structure of the molecules. Arrangements of submonolayer, monolayer, and monolayer with additional adsorbed molecules have been investigated. The high resolution of our investigations has permitted us to image single molecule orientation. The molecular plane is found to be oriented parallel to the substrate surface and a square adsorption unit cell of the molecules is reported. In addition, depending on the bias voltage, different electronic states of the molecules have been probed. The characterized molecular states are in excellent agreement with density functional theory ground state simulations of a single molecule. Additional molecules adsorbed on the monolayer structures have been observed, and it is found that the second layer molecules adsorb flat and on top of the molecules in the first layer. All STM measurements presented here have been performed at a sample temperature of 70 K.