An in-situ surface electrochemistry approach toward whole-cell studies: Charge transfer between Geobacter sulfurreducens and electrified metal/electrolyte interfaces through linker molecules

Electrochemical reactivity and structure properties of electrogenic bacteria, Geobacter sulfurreducens (Gs) were studied to explore the heterogeneous electron transfer at the bacteria/electrode interface using electrochemical and in-situ spectroscopic techniques. The redox behavior of Gs adsorbed on a gold electrode, which is modified with a ω-functionalized self-assembled monolayer (SAM) of alkanethiols, depends strongly on the terminal group. The latter interacts directly with outermost cytochromes embedded into the outer membrane of the Gs cells. The redox potential of bacterial cells bound electrostatically to a carboxyl-terminated SAM is close to that observed for bacteria attached to a bare gold electrode, revealing a high electronic coupling at the cell/SAM interface. The redox potentials of bacterial cells adsorbed on amino- and pyridyl-terminated SAMs are significantly different suggesting that the outermost cytochromes changes their conformation upon adsorption on these SAMs. No redox activity of Gs was found with CH3-, N(CH3)3+- and OH-terminated SAMs. Complementary in-situ spectroscopic studies on bacteria/SAMs/Au electrode assemblies were carried out to monitor structure changes of the bacterial cells upon polarization. Spectro-electrochemical techniques revealed the electrochemical turnover of the oxidized and reduced states of outer membrane cytochromes (OMCs) in Gs, providing evidence that the OMCs are responsible for the direct electron transfer to metal electrodes, such as gold or silver, during the electricity production. Furthermore, we observed spectroscopic signatures of the native structure of the OMCs and no conformational change during the oxidation/reduction process of the microorganisms. These findings indicate that the carboxyl-anchoring group provides biocompatible conditions for the outermost cytochromes of the Gs, which facilitate the heterogeneous electron transfer at the microorganism/electrode interface.

Electrochemical characterization of self-assembled Ferrocene-terminated alkanethiol monolayers on low-index gold single crystal electrodes

We present a voltammetric and in situ STM study of 11-ferrocenyl-1-undecanethiol (FcC11) assembled on low-index single crystal and polycrystalline gold electrodes. The influence of electrode surface structure as well as of structure defects in the self-assembled FcC11 monolayers on the electrochemical response during the oxidation and reduction of the terminal ferrocene group is explored. The nature of the redox peaks is discussed in detail. We identified the coexistence of disordered FcC11 regions with 2D patches of “locally ordered” FcC11 species. We demonstrate that close-packed domains are preferentially formed at atomically flat terraces. Increasing the defect density of the substrate surface leads to a decreasing amount of locally ordered FcC11 molecules.

Tn6198, a novel transposon containing the trimethoprim resistance gene dfrG embedded into a Tn916 element in Listeria monocytogenes

OBJECTIVES: To characterize Tn6198, a novel conjugative transposon from the clinical Listeria monocytogenes strain TTH-2007, which contains the tetracycline and trimethoprim resistance genes tet(M) and dfrG, respectively, and to assess its transferability in vitro and in situ. METHODS: The complete sequence of Tn6198 was determined using a primer walking strategy. Horizontal gene transfer studies were performed by filter matings, as well as on the surface of smear-ripened cheese and smoked salmon. The presence of Tn916-like circular intermediates was determined by PCR. Antibiotic resistance was determined by the broth microdilution method and microarray hybridization. RESULTS: Sequencing of Tn6198 revealed that a 3.3 kb fragment containing dfrG was integrated between open reading frames 23 and 24 of Tn916. Furthermore, an additional copy of Tn916 was present in L. monocytogenes TTH-2007. Both elements were transferred simultaneously and separately in vitro to recipients L. monocytogenes 10403S and Enterococcus faecalis JH2-2 by conjugation, resulting in either tetracycline- and trimethoprim-resistant or solely tetracycline-resistant transconjugants. On the surface of cheese and salmon, only L. monocytogenes 10403S transconjugants were detected. CONCLUSIONS: This study reports the first Tn916-like element associated with a trimethoprim resistance gene, as well as the first fully characterized transposon conferring multidrug resistance in L. monocytogenes. This is of concern, as trimethoprim is administered to listeriosis patients with β-lactam allergy and as Tn6198 has a large potential for dissemination, indicated by both intra-species and inter-genus transfer.

Analysis of fractal electrodes for efficient neural stimulation

Planar electrodes are increasingly used in therapeutic neural stimulation techniques such as functional electrical stimulation, epidural spinal cord stimulation (ESCS), and cortical stimulation. Recently, optimized electrode geometries have been shown to increase the efficiency of neural stimulation by increasing the variation of current density on the electrode surface. In the present work, a new family of modified fractal electrode geometries is developed to enhance the efficiency of neural stimulation. It is shown that a promising approach in increasing the neural activation function is to increase the "edginess" of the electrode surface, a concept that is explained and quantified by fractal mathematics. Rigorous finite element simulations were performed to compute electric potential produced by proposed modified fractal geometries. The activation of 256 model axons positioned around the electrodes was then quantified, showing that modified fractal geometries required a 22% less input power while maintaining the same level of neural activation. Preliminary in vivo experiments investigating muscle evoked potentials due to median nerve stimulation showed encouraging results, supporting the feasibility of increasing neural stimulation efficiency using modified fractal geometries.

Electrodes for Long-Term Esophageal Electrocardiography

The emerging application of long-term and high-quality ECG recording requires alternative electrodes to improve the signal quality and recording capability of surface skin electrodes. The esophageal ECG has the potential to overcome these limitations but necessitates novel recorder and lead designs. The electrode material is of particular interest, since the material has to ensure conflicting requirements like excellent biopotential recording properties and inertness. To this end, novel electrode materials like PEDOT and silver-PDMS as well as established electrode materials such as stainless steel, platinum, gold, iridium oxide, titanium nitride, and glassy carbon were investigated by long-term electrochemical impedance spectroscopy and model-based signal analysis using the derived in vitro interfacial properties in conjunction with a dedicated ECG amplifier. The results of this novel approach show that titanium nitride and iridium oxide featuring microstructured surfaces did not degrade when exposed to artificial acidic saliva. These materials provide low electrode potential drifts and insignificant signal distortion superior to surface skin electrodes making them compatible with accepted standards for ambulatory ECG. They are superior to the noble and polarizable metals such as platinum, silver, and gold that induced more signal distortions and are superior to esophageal stainless steel electrodes that corrode in artificial saliva. The study provides rigorous criteria for the selection of electrode materials for prolonged ECG recording by combining long-term in vitro electrode material properties with ECG signal quality assessment.

Finite element analyses of human vertebral bodies embedded in polymethylmethalcrylate or loaded via the hyperelastic intervertebral disc models provide equivalent predictions of experimental strength

Quantitative computer tomography (QCT)-based finite element (FE) models of vertebral body provide better prediction of vertebral strength than dual energy X-ray absorptiometry. However, most models were validated against compression of vertebral bodies with endplates embedded in polymethylmethalcrylate (PMMA). Yet, loading being as important as bone density, the absence of intervertebral disc (IVD) affects the strength. Accordingly, the aim was to assess the strength predictions of the classic FE models (vertebral body embedded) against the in vitro and in silico strengths of vertebral bodies loaded via IVDs. High resolution peripheral QCT (HR-pQCT) were performed on 13 segments (T11/T12/L1). T11 and L1 were augmented with PMMA and the samples were tested under a 4° wedge compression until failure of T12. Specimen-specific model was generated for each T12 from the HR-pQCT data. Two FE sets were created: FE-PMMA refers to the classical vertebral body embedded model under axial compression; FE-IVD to their loading via hyperelastic IVD model under the wedge compression as conducted experimentally. Results showed that FE-PMMA models overestimated the experimental strength and their strength prediction was satisfactory considering the different experimental set-up. On the other hand, the FE-IVD models did not prove significantly better (Exp/FE-PMMA: R²=0.68; Exp/FE-IVD: R²=0.71, p=0.84). In conclusion, FE-PMMA correlates well with in vitro strength of human vertebral bodies loaded via real IVDs and FE-IVD with hyperelastic IVDs do not significantly improve this correlation. Therefore, it seems not worth adding the IVDs to vertebral body models until fully validated patient-specific IVD models become available.

Electrochemical simulation of phase I metabolism for 21 drugs using four different working electrodes in an automated screening setup with MS detection.

BACKGROUND Electrochemical conversion of xenobiotics has been shown to mimic human phase I metabolism for a few compounds. MATERIALS & METHODS Twenty-one compounds were analyzed with a semiautomated electrochemical setup and mass spectrometry detection. RESULTS The system was able to mimic some metabolic pathways, such as oxygen gain, dealkylation and deiodination, but many of the expected and known metabolites were not produced. CONCLUSION Electrochemical conversion is a useful approach for the preparative synthesis of some types of metabolites, but as a screening method for unknown phase I metabolites, the method is, in our opinion, inferior to incubation with human liver microsomes and in vivo experiments with laboratory animals, for example.

(Non)-Dissipative Hydrodynamics on Embedded Surfaces

We construct the theory of dissipative hydrodynamics of uncharged fluids living on embedded space-time surfaces to first order in a derivative expansion in the case of codimension-1 surfaces (including fluid membranes) and the theory of non-dissipative hydrodynamics to second order in a derivative expansion in the case of codimension higher than one under the assumption of no angular momenta in transverse directions to the surface. This construction includes the elastic degrees of freedom, and hence the corresponding transport coefficients, that take into account transverse fluctuations of the geometry where the fluid lives. Requiring the second law of thermodynamics to be satisfied leads us to conclude that in the case of codimension-1 surfaces the stress-energy tensor is characterized by 2 hydrodynamic and 1 elastic independent transport coefficient to first order in the expansion while for codimension higher than one, and for non-dissipative flows, the stress-energy tensor is characterized by 7 hydrodynamic and 3 elastic independent transport coefficients to second order in the expansion. Furthermore, the constraints imposed between the stress-energy tensor, the bending moment and the entropy current of the fluid by these extra non-dissipative contributions are fully captured by equilibrium partition functions. This analysis constrains the Young modulus which can be measured from gravity by elastically perturbing black branes.