Eduardo Cortón

Rapid identification of viable Escherichia coli subspecies with an electrochemical screen-printed biosensor array.

Rapid identification of Escherichia coli strains is an important diagnostic goal in applied medicine as well as the environmental and food sciences. This paper reports an electrochemical, screen-printed biosensor array, where selective recognition is accomplished using lectins that recognize and bind to cell-surface lipopolysaccharides and coulometric transduction exploits non-native external oxidants to monitor respiratory cycle activity in lectin-bound cells. Ten different lectins were separately immobilized onto porous membranes that feature activated surfaces (ImmunodyneABC). Modified membranes were exposed to untreated E. coli cultures for 30 min, rinsed, and layered over the individual screen-printed carbon electrodes of the sensor array. The membranes were were incubated 5 min in a reagent solution that contained the oxidants menadione and ferricyanide as well as the respiratory substrates succinate and formate. Electrochemical oxidation of ferrocyanide for 2 min provided chronocoulometric data related to the quantities of bound cells. These screen-printed sensor arrays were used in conjunction with factor analysis for the rapid identification of four E. coli subspecies (E. coli B, E. coli Neotype, E. coli JM105 and E. coli HB101). Systematic examination of lectin-binding patterns showed that these four E. coli subspecies are readily distinguished using only five essential lectins.

Osmium complexes bearing functional groups: building blocks for integrated chemical systems

Abstract Two new redox-active osmium complexes of the type (Os(bpy)2Cl(pyX))+ have been synthesised, where pyX corresponds to a pyridine derivative bearing a functional group (aldehyde, carboxylate). Their electrochemical behaviour and electronic spectra were studied in acetonitrile and aqueous solutions. The rate coefficients for the re-oxidation of glucose oxidase (GOx) by these new osmium complexes were obtained. The applicability to this system of the equation derived by Nicholson and Shain for an EC′ mechanism is discussed. The mediator containing the carbonyl group was bound to poly(allyl)amine. The new electroactive polymer was wired with oxidases in the construction of glucose and lactate sensors, as an example of the capabilities of these new osmium complexes to build integrated chemical systems.

Analytical applications of microbial fuel cells. Part I: Biochemical oxygen demand

Microbial fuel cells (MFCs) are bio-electrochemical devices, where usually the anode (but sometimes the cathode, or both) contains microorganisms able to generate and sustain an electrochemical gradient which is used typically to generate electrical power. In the more studied set-up, the anode contains heterotrophic bacteria in anaerobic conditions, capable to oxidize organic molecules releasing protons and electrons, as well as other by-products. Released protons could reach the cathode (through a membrane or not) whereas electrons travel across an external circuit originating an easily measurable direct current flow. MFCs have been proposed fundamentally as electric power producing devices or more recently as hydrogen producing devices. Here we will review the still incipient development of analytical uses of MFCs or related devices or set-ups, in the light of a non-restrictive MFC definition, as promising tools to asset water quality or other measurable parameters. An introduction to biological based analytical methods, including bioassays and biosensors, as well as MFCs design and operating principles, will also be included. Besides, the use of MFCs as biochemical oxygen demand sensors (perhaps the main analytical application of MFCs) is discussed. In a companion review (Part 2), other new analytical applications are reviewed used for toxicity sensors, metabolic sensors, life detectors, and other proposed applications.

An Os(byp)2ClPyCH2NHPoly(allylamine) hydrogel mediator for enzyme wiring at electrodes

An Os hydrogel based on the covalent attachment of Os(byp)2 ClPyCHO to PAA-NH2 was cross-linked with glucose oxidase (GOx), lactate oxidase (LOx) and horseradish peroxidase (HRP) on GC and Au electrodes by PEG-400 bifunctional reagent. Single layer monoenzyme (GOx or LOx) and bienzyme (HRP-GOx) single layer modified electrodes were prepared with the Os moieties acting as “electron wires or electron shuttles”. Cyclic voltammetry showed diffusional charge propagation in the gel which resulted more stable than similar ferrocene based gels reported before. In solutions containing the substrates, catalytic currents were obtained due to enzyme catalysis for the oxidation of glucose and lactate by the respective enzymes mediated by the Os polymer either by detecting directly the anodic current in a single enzyme electrode or indirectly by further reducing the peroxide formed in the aerobic enzymatic cycle at the Os-wired HRP. A rotating disc electrode (RDE) and a wall jet electrode (WJE) were employed as hydrodynamic electrodes in order to correct the amperometric response for substrate concentration polarization in the external electrolyte.

Analytical applications of microbial fuel cells. Part II: Toxicity, microbial activity and quantification, single analyte detection and other uses.

Microbial fuel cells were rediscovered twenty years ago and now are a very active research area. The reasons behind this new activity are the relatively recent discovery of electrogenic or electroactive bacteria and the vision of two important practical applications, as wastewater treatment coupled with clean energy production and power supply systems for isolated low-power sensor devices. Although some analytical applications of MFCs were proposed earlier (as biochemical oxygen demand sensing) only lately a myriad of new uses of this technology are being presented by research groups around the world, which combine both biological-microbiological and electroanalytical expertises. This is the second part of a review of MFC applications in the area of analytical sciences. In Part I a general introduction to biological-based analytical methods including bioassays, biosensors, MFCs design, operating principles, as well as, perhaps the main and earlier presented application, the use as a BOD sensor was reviewed. In Part II, other proposed uses are presented and discussed. As other microbially based analytical systems, MFCs are satisfactory systems to measure and integrate complex parameters that are difficult or impossible to measure otherwise, such as water toxicity (where the toxic effect to aquatic organisms needed to be integrated). We explore here the methods proposed to measure toxicity, microbial metabolism, and, being of special interest to space exploration, life sensors. Also, some methods with higher specificity, proposed to detect a single analyte, are presented. Different possibilities to increase selectivity and sensitivity, by using molecular biology or other modern techniques are also discussed here.

Enhanced Analytical Performance of Paper Microfluidic Devices by Using Fe3O4 Nanoparticles, MWCNT, and Graphene Oxide.

Spheres, tubes, and planar-shaped nanomaterials as Fe3O4 nanoparticles (MNPs), multiwalled carbon nanotubes (MWCNT), and graphene oxide (GO) were used for the first time to treat microfluidic paper-based analytical devices (μPADs) and create a biocompatible layer with high catalytic surface. Once glucose measurements are critical for diabetes or glycosuria detection and monitoring, the analytical performance of the proposed devices was studied by using bienzymatic colorimetric detection of this carbohydrate. The limit of detection values achieved for glucose with μPADs treated with MNPs, MWCNT, and GO were 43, 62, and 18 μM, respectively. The paper surface modification solves problems associated with the lack of homogeneity on color measurements that compromise the sensitivity and detectability levels in clinical diagnosis.

Voltamperometric Discrimination of Urea and Melamine Adulterated Skimmed Milk Powder

Nitrogen compounds like urea and melamine are known to be commonly used for milk adulteration resulting in undesired intoxication; a well-known example is the Chinese episode occurred in 2008. The development of a rapid, reliable and economic test is of relevance in order to improve adulterated milk identification. Cyclic voltammetry studies using an Au working electrode were performed on adulterated and non-adulterated milk samples from different independent manufacturers. Voltammetric data and their first derivative were subjected to functional principal component analysis (f-PCA) and correctly classified by the KNN classifier. The adulterated and non-adulterated milk samples showed significant differences. Best results of prediction were obtained with first derivative data. Detection limits in milk samples adulterated with 1% of its total nitrogen derived from melamine or urea were as low as 85.0 mg·L−1 and 121.4 mg·L−1, respectively. We present this method as a fast and robust screening method for milk adulteration analysis and prevention of food intoxication.

Characterization of Lactobacillus Carbohydrate Fermentation Activity Using Immobilized Cell Technique

A microbial bioreactor based on calcium alginate immobilized Lactobacillus cells coupled to a pH electrode was developed for quantitative determination of carbohydrate fermentation activity. A high biomass (1010 cfu mL−1) and particular pregrowth conditions were needed. Reduction of catabolite repression by monosaccharides was achieved by pregrowth in lactose. The evolution of acid production in a continuous flow‐stopped flow bioreactor was monitored for different sugar solutions in contact with the immobilized bacteria. The resulting slopes (ΔmV/Δt) were used to quantify the fermentation capability for a defined sugar related to that of glucose, which was taken as 100%. The procedure is simple, being based on pH variation that can give quantitative results compared to other reported techniques for carbohydrate fermentation pattern from which only qualitative results are obtained. In addition, it offers reduction in time and costs and is a suitable tool for the rapid analysis of isolated strains and in studies of modifications of sugar metabolism in mutants.

Performance of planar and cylindrical carbon electrodes at sedimentary microbial fuel cells

This paper presents data obtained using an indigenous microbial community contained in anaerobic sediments (mud) collected from the shore of the Río de La Plata River (South America). After the sedimentary microbial fuel cells were assembled the evolution of current and power vs. time was studied. Two types of commercially available graphite materials were used as electrodes, which differ mainly in shape and size. In some experiments, an external carbon source (acetate) increased the power generation rate. The maximum power density observed in the aforementioned condition was 19.57 ± 0.35 and 8.72 ± 1.39 mW/m(2) using rod and graphite disk electrodes, respectively. The better performance of the rod electrodes can be explained, at least in part, by an enhanced rate of mass transport by radial diffusion. DGGE fingerprints were used to study the electrogenic community growing over the electrodes.

Comparative Survival Analysis of Deinococcus radiodurans and the Haloarchaea Natrialba magadii and Haloferax volcanii Exposed to Vacuum Ultraviolet Irradiation

The haloarchaea Natrialba magadii and Haloferax volcanii, as well as the radiation-resistant bacterium Deinococcus radiodurans, were exposed to vacuum UV (VUV) radiation at the Brazilian Synchrotron Light Laboratory. Cell monolayers (containing 10(5) to 10(6) cells per sample) were prepared over polycarbonate filters and irradiated under high vacuum (10(-5) Pa) with polychromatic synchrotron radiation. N. magadii was remarkably resistant to high vacuum with a survival fraction of (3.77±0.76)×10(-2), which was larger than that of D. radiodurans (1.13±0.23)×10(-2). The survival fraction of the haloarchaea H. volcanii, of (3.60±1.80)×10(-4), was much smaller. Radiation resistance profiles were similar between the haloarchaea and D. radiodurans for fluences up to 150 J m(-2). For fluences larger than 150 J m(-2), there was a significant decrease in the survival of haloarchaea, and in particular H. volcanii did not survive. Survival for D. radiodurans was 1% after exposure to the higher VUV fluence (1350 J m(-2)), while N. magadii had a survival lower than 0.1%. Such survival fractions are discussed regarding the possibility of interplanetary transfer of viable microorganisms and the possible existence of microbial life in extraterrestrial salty environments such as the planet Mars and Jupiters moon Europa. This is the first work to report survival of haloarchaea under simulated interplanetary conditions.