Cable Bacteria Skeletons as Catalytically Active Electrodes.

Cable bacteria are multicellular, filamentous bacteria that use internal conductive fibers to transfer electrons over centimeter distances from donors within anoxic sediment layers to oxygen at the surface. We extracted the fibers and used them as free-standing bio-based electrodes to investigate their electrocatalytic behavior. The fibers catalyzed the reversible interconversion of oxygen and water, and an electric current was running through the fibers even when the potential difference was generated solely by a gradient of oxygen concentration. Oxygen reduction as well as oxygen evolution were confirmed by optical measurements. Within living cable bacteria, oxygen reduction by direct electrocatalysis on the fibers and not by membrane-bound proteins readily explains exceptionally high cell-specific oxygen consumption rates observed in the oxic zone, while electrocatalytic water oxidation may provide oxygen to cells in the anoxic zone.

Microwave Gas Sensors Based on Electrodeposited Polypyrrole-Nickel Phthalocyanine Hybrid Films.

Previous studies have shown that the incorporation of sulfonated metallophthalocyanines into sensitive sensor materials can improve electron transfer and thus species detection. Herein, we propose a simple and easy alternative to the use of generally expensive sulfonated phthalocyanines by electropolymerizing polypyrrole together with nickel phthalocyanine in the presence of an anionic surfactant. The addition of the surfactant not only helps the incorporation of the water-insoluble pigment into the polypyrrole film, but the obtained structure has increased hydrophobicity, which is a key property for developing efficient gas sensors with low sensitivity to water. The obtained results show the effectiveness of the materials tested for the detection of ammonia in the range of 100 to 400 ppm. It is shown by comparing the microwave sensor responses that the film without nickel phthalocyanine (hydrophilic) produces greater variations than the film with nickel phthalocyanine (hydrophobic). These results are consistent with the expected results since the hydrophobic film is not very sensitive to residual ambient water and therefore does not interfere with the microwave response. However, although this excess response is usually a handicap, as it is a source of drift, in these experiments the microwave response shows great stability in both cases.

Electrochemical Biosensing of Dopamine Neurotransmitter: A Review.

Neurotransmitters are biochemical molecules that transmit a signal from a neuron across the synapse to a target cell, thus being essential to the function of the central and peripheral nervous system. Dopamine is one of the most important catecholamine neurotransmitters since it is involved in many functions of the human central nervous system, including motor control, reward, or reinforcement. It is of utmost importance to quantify the amount of dopamine since abnormal levels can cause a variety of medical and behavioral problems. For instance, Parkinson's disease is partially caused by the death of dopamine-secreting neurons. To date, various methods have been developed to measure dopamine levels, and electrochemical biosensing seems to be the most viable due to its robustness, selectivity, sensitivity, and the possibility to achieve real-time measurements. Even if the electrochemical detection is not facile due to the presence of electroactive interfering species with similar redox potentials in real biological samples, numerous strategies have been employed to resolve this issue. The objective of this paper is to review the materials (metals and metal oxides, carbon materials, polymers) that are frequently used for the electrochemical biosensing of dopamine and point out their respective advantages and drawbacks. Different types of dopamine biosensors, including (micro)electrodes, biosensing platforms, or field-effect transistors, are also described.

Cooperative Chemotaxis of Magnesium Microswimmers for Corrosion Spotting.

Numerous artificial micro- and nanomotors, as well as various swimmers have been inspired by living organisms that are able to move in a coordinated manner. Their cooperation has also gained a lot of attention because the resulting clusters are able to adapt to changes in their environment and to perform complex tasks. However, mimicking such a collective behavior remains a challenge. In the present work, magnesium microparticles are used as chemotactic swimmers with pronounced collective features, allowing the gradual formation of macroscopic agglomerates. The formed clusters act like a single swimmer able to follow pH gradients. This dynamic behavior can be used to spot localized corrosion events in a straightforward way. The autonomous docking of the swimmers to the corrosion site leads to the formation of a local protection layer, thus increasing corrosion resistance and triggering partial self-healing.

Lipid-coated mesoporous silica microparticles for the controlled delivery of ß-galactosidase into intestines.

ß-Galactosidase has been drawing increasing attention for the treatment of lactose intolerance, but its delivery has been impeded by degradation under gastric conditions. We have demonstrated that the coating of mesoporous silica microparticles (diameter ≈ 9 µm, pore size ≈ 25 nm) with dioleoylphosphatidylcholine membranes significantly improved the loading capability and protected the enzymes from the loss of function under simulated gastric conditions. Once the particles are transferred to simulated intestinal conditions, the digestion of phosphatidylcholine with pancreatin led to the release of functional ß-galactosidase. The coating of mesoporous silica nanoparticles with a single phospholipid bilayer opens up a large potential towards the controlled release of orally administrated drugs or enzymes to the intestines.

Effect of Meso vs Macro Size of Hierarchical Porous Silica on the Adsorption and Activity of Immobilized ß-Galactosidase.

ß-Galactosidase (ß-Gal) is one of the most important enzymes used in milk processing for improving their nutritional quality and digestibility. Herein, ß-Gal has been entrapped into a meso-macroporous material (average pore size 9 and 200 nm, respectively) prepared by a sol-gel method from a silica precursor and a dispersion of solid lipid nanoparticles in a micelle phase. The physisorption of the enzyme depends on the concentration of the feed solution and on the pore size of the support. The enzyme is preferentially adsorbed either in mesopores or in macropores, depending on its initial concentration. Moreover, this selective adsorption, arising from the oligomeric complexation of the enzyme (monomer/dimer/tetramer), has an effect on the catalytic activity of the material. Indeed, the enzyme encapsulated in macropores is more active than the enzyme immobilized in mesopores. Designed materials containing ß-Gal are of particular interest for food applications and potentially extended to bioconversion, bioremediation, or biosensing when coupling the designed support with other enzymes.

Sensing based on the motion of enzyme-modified nanorods.

Asymmetric modification with an enzyme confers nanorods an enhanced diffusive motion that is dependent on the concentration of the enzyme substrate. In turn, such a motion opens the possibility of determining the concentration of the enzyme substrate by measuring the diffusion coefficient of nanorods modified with the appropriate enzyme. Nanorods, with a Pt and a polypyrrole (PPy) segment, were fabricated. The PPy segment of such nanorods was then modified with glucose oxidase (GOx), glutamate oxidase (GluOx), or xanthine oxidase (XOD). Calibration curves, linking the diffusion coefficient of the oxidase-modified nanorods to the concentration of the oxidase substrate, were subsequently built. The oxidase-modified nanorods and their calibration curves were finally used to determine substrate concentrations both in simple aqueous solutions and in complex samples such as horse serum and cell culture media. Based on the obtained results we are confident that our motion-based approach to sensing can be developed to the point where different nanorods in a mixture simultaneously report on the concentration of different compounds with good temporal and spatial resolution.

Modification with hemeproteins increases the diffusive movement of nanorods in dilute hydrogen peroxide solutions.

Nanorods were decorated with different hemeproteins that are able to convert hydrogen peroxide. When dispersed into hydrogen peroxide solutions, most of these nanorods are characterized by diffusion coefficients which increase with the concentration of hydrogen peroxide. Such a behaviour does not characterize unmodified nanorods.