Nanoporous Gold Biointerfaces: Modifying Nanostructure to Control Neural Cell Coverage and Enhance Electrophysiological Recording Performance

Nanostructured neural interface coatings have significantly enhanced recording fidelity in both implantable and in vitro devices. As such, nanoporous gold (np‐Au) has shown promise as a multifunctional neural interface coating due, in part, to its ability to promote nanostructure‐mediated reduction in astrocytic surface coverage while not affecting neuronal coverage. The goal of this study is to provide insight into the mechanisms by which the np‐Au nanostructure drives the differential response of neurons versus astrocytes in an in vitro model. Utilizing microfabricated libraries that display varying feature sizes of np‐Au, it is demonstrated that np‐Au influences neural cell coverage through modulating focal adhesion formation in a feature size‐dependent manner. The results here show that surfaces with small (≈30 nm) features control astrocyte spreading through inhibition of focal adhesion formation, while surfaces with large (≈170 nm and greater) features control astrocyte spreading through other mechanotransduction mechanisms. This cellular response combined with lower electrical impedance of np‐Au electrodes significantly enhances the fidelity and stability of electrophysiological recordings from cortical neuron‐glia co‐cultures relative to smooth gold electrodes. Finally, by leveraging the effect of nanostructure on neuronal versus glial cell attachment, the use of laser‐based nanostructure modulation is demonstrated for selectively patterning neurons with micrometer spatial resolution.     

Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates

A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO⁻], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm⁻¹. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol⁻¹ cm⁻¹, and the integrated molar absorptivity is 2.95 ± 0.08 × 10⁴ l mol⁻¹ cm⁻² (n = 15 compounds, 0.1 M ≤ [COO⁻] ≤ 1.5 M). The [COO⁻] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO⁻ groups.     

Phylogenetics of worldwide human populations as determined by polymorphic Alu insertions

Alu elements, the largest family of interspersed repeats, mobilize throughout the genomes of primates by retroposition. Alu are present in humans in an excess of 500 000 copies per haploid genome. Since some of the insertion alleles have not reached fixation, they remain polymorphic and can be used as biallelic DNA marker systems in investigations of human evolution. In this study, six polymorphic Alu insertional (PAI) loci were used as genetic markers. These markers are thought to be selectively neutral. The presence of these six PAIs was determined by a polymerase chain reaction (PCR)-based assay in 1646 individuals from 47 populations from around the world. Examination of the populations by plotting the first and second principal components, shows the expected segregation of populations according to geographical vicinity and established ethnic affinities. Centroid analysis demonstrated that sub-Sahara populations have experienced higher than average gene flow and/or represent larger populations as compared to groups in other parts of the globe and especially to known inbreed populations. This is consistent with greater heterogeneity and diversity expected of source groups. In addition, maximum likelihood (ML) analyses were performed with these 47 populations and a hypothetical ancestral group lacking the insertion in all six loci. Analysis of our data supports the Out of Africa hypothesis. African populations and admixed groups of African descent formed a single monophyletic group with a basal placement on the tree, which grouped closest to the hypothetical ancestor.     

Determination of serum aluminum by electrothermal atomic absorption spectrometry: A comparison between Zeeman and continuum background correction systems

Excessive exposure to aluminum (Al) can produce serious health consequences in people with impaired renal function, especially those undergoing hemodialysis. Al can accumulate in the brain and in bone, causing dialysis-related encephalopathy and renal osteodystrophy. Thus, dialysis patients are routinely monitored for Al overload, through measurement of their serum Al. Electrothermal atomic absorption spectrometry (ETAAS) is widely used for serum Al determination. Here, we assess the analytical performances of three ETAAS instruments, equipped with different background correction systems and heating arrangements, for the determination of serum Al. Specifically, we compare (1) a Perkin Elmer (PE) Model 3110 AAS, equipped with a longitudinally (end) heated graphite atomizer (HGA) and continuum-source (deuterium) background correction, with (2) a PE Model 4100ZL AAS equipped with a transversely heated graphite atomizer (THGA) and longitudinal Zeeman background correction, and (3) a PE Model Z5100 AAS equipped with a HGA and transverse Zeeman background correction. We were able to transfer the method for serum Al previously established for the Z5100 and 4100ZL instruments to the 3110, with only minor modifications. As with the Zeeman instruments, matrix-matched calibration was not required for the 3110 and, thus, aqueous calibration standards were used. However, the 309.3-nm line was chosen for analysis on the 3110 due to failure of the continuum background correction system at the 396.2-nm line. A small, seemingly insignificant overcorrection error was observed in the background channel on the 3110 instrument at the 309.3-nm line. On the 4100ZL, signal oscillation was observed in the atomization profile. The sensitivity, or characteristic mass (m₀), for Al at the 309.3-nm line on the 3110 AAS was found to be 12.1 ± 0.6 pg, compared to 16.1 ± 0.7 pg for the Z5100, and 23.3 ± 1.3 pg for the 4100ZL at the 396.2-nm line. However, the instrumental detection limits (3 SD) for Al were very similar: 3.0, 3.2, and 4.1 μg L^− 1 for the Z5100, 4100ZL, and 3110, respectively. Serum Al method detection limits (3 SD) were 9.8, 6.9, and 7.3 μg L^− 1, respectively. Accuracy was assessed using archived serum (and plasma) reference materials from various external quality assessment schemes (EQAS). Values found with all three instruments were within the acceptable EQAS ranges. The data indicate that relatively modest ETAAS instrumentation equipped with continuum background correction is adequate for routine serum Al monitoring.     

Synthesis and circular dichroism of tetraarylporphyrin-oligonucleotide conjugates

The preparation and circular dichroic (CD) studies of self-complimentary 8-mer DNA sequences with a porphyrin at the 3' end are presented. Electronic interaction between the two porphyrins (the interchromophoric distance is in the range of 28-40 A), attached to both ends of the double-stranded helix, gives rise to a long-range exciton-coupled CD in the visible region (400-450 nm). The porphyrin chromophores act as sensitive probes of geometrical changes in the DNA backbone and sensitively reflect the double-strand to single-strand transition. This study demonstrates the possibility of using exciton-coupled porphyrin CDs for conformational studies of DNA.     

Dilute sulfuric acid hydrolysis of biomass for ethanol production

A series of pilot plant experiments have been conducted to compare the performance of a system utilizing two percolation reactors in series to a single reactor system. Although theoretically capable of producing higher glucose yields or concentrations, the two-reactor system concentrations were approximately the same and the yields were considerably lower than those from the single reactor study. An associated kinetics study found the glucose degradation kinetics to be accelerated by chromium ions, but this effect was greatly reduced in the presence of wood. The presence of metal surfaces also increased the rate of degradation even without large ion concentrations. The poor performance of the reactor system is proposed to be caused by intraparticle glucose diffusion effects and the catalytic effect on glucose degradation reactions of chromium ions from the corrosion of stainless steel by the acid. Strategies for reducing the effects of these phenomena on PBR performance are presented.

     

Etchant solutions for the removal of Cu(0) in a supercritical CO2-based "dry" chemical mechanical planarization process for device fabrication

The microelectronics industry is focused on increasing chip complexity, improving the density of electron carriers, and decreasing the dimensions of the interconnects into the sub-0.25 mum regime while maintaining high aspect ratios. Water-based chemical mechanical planarization or polishing (CMP) faces several technical and environmental challenges. Condensed CO2 has significant potential for replacing current CMP solvents as a "dry" etching medium because of its unique properties. In working toward a condensed CO2-based CMP process, we have successfully investigated the oxidation and chelation of solid copper metal in liquid and supercritical CO2 using ethyl peroxydicarbonate and a beta-diketone chelating agent.