Influence of anode pretreatment on its microbial colonization

AIMS

To assess the influence of chemical treatment of the anode of a marine sediment biofuel cell (MSBFC) on the microbial diversity of the anode biofilm.

METHODS AND RESULTS

A MSBFC was equipped with two graphite plate anodes, one pretreated by electrochemical oxidation in sulfuric acid and the other untreated. After 6 weeks of operation, 16S rRNA clone libraries were constructed from each anode biofilm. The pretreated anode exhibited a fourfold depletion in gamma-proteobacteria, a fourfold enrichment in delta-proteobacteria, a sixfold increase in sulfate reducers, a fivefold enrichment in unclassified micro-organisms, and 6% of the colonies were sulfur oxidizers while none were detected on the untreated anode.

CONCLUSION

Anode pretreatment significantly affects the anode-colonized microbial communities of MSBFCs.

SIGNIFICANCE AND IMPACT OF THE STUDY

The MSBFC is one of a new class of microbial fuel cells in which the anode is spontaneously colonized by a subset of micro-organisms indigenous to a complex anaerobic mixture (such as sewage and food processing effluents). These micro-organisms utilize the anode as an oxidant, catalysing power generation by oxidizing fuel in the mixture and reducing the anode. This study reveals that pretreatment of the anode can greatly affect the composition of the microbial colony of such fuel cells.

Synthesis and characterization of a ruthenium(II)-based redox conjugate for reagentless biosensing

Synthesis of a novel sulfhydryl-specific, tetraammine Ru(II)polypyridyl complex, [Ru(II)(NH(3))(4)(1,10-phenanthroline-5-maleimide)](PF(6))(2), which exhibits environment-sensitive electrochemical properties is described. When conjugated to an allosteric site in a genetically engineered mutant of maltose binding protein, the formal potential of the conjugated redox probe is shifted to higher potential upon maltose binding. The magnitude of this potential shift was used to measure maltose affinity of the protein-redox conjugate complex and to monitor maltose concentration in solution. These results are presented in context of reagentless biosensing.

Harvesting energy from the marine sediment--water interface

Pairs of platinum mesh or graphite fiber-based electrodes, one embedded in marine sediment (anode), the other in proximal seawater (cathode), have been used to harvest low-level power from natural, microbe established, voltage gradients at marine sediment-seawater interfaces in laboratory aquaria. The sustained power harvested thus far has been on the order of 0.01 W/m2 of electrode geometric area but is dependent on electrode design, sediment composition, and temperature. It is proposed that the sediment/anode-seawater/cathode configuration constitutes a microbial fuel cell in which power results from the net oxidation of sediment organic matter by dissolved seawater oxygen. Considering typical sediment organic carbon contents, typical fluxes of additional reduced carbon by sedimentation to sea floors < 1,000 m deep, and the proven viability of dissolved seawater oxygen as an oxidant for power generation by seawater batteries, it is calculated that optimized power supplies based on the phenomenon demonstrated here could power oceanographic instruments deployed for routine long-term monitoring operations in the coastal ocean.

Array biosensor for simultaneous identification of bacterial, viral, and protein analytes

The array biosensor was fabricated to analyze multiple samples simultaneously for multiple analytes. The sensor utilized a standard sandwich immunoassay format: Antigen-specific "capture" antibodies were immobilized in a patterned array on the surface of a planar waveguide and bound analyte was subsequently detected using fluorescent tracer antibodies. This study describes the analysis of 126 blind samples for the presence of three distinct classes of analytes. To address potential complications arising from using a mixture of tracer antibodies in the multianalyte assay, three single-analyte assays were run in parallel with a multianalyte assay. Mixtures of analytes were also assayed to demonstrate the sensor's ability to detect more than a single species at a time. The array sensor was capable of detecting viral, bacterial, and protein analytes using a facile 14-min assay with sensitivity levels approaching those of standard ELISA methods. Limits of detection for Bacillus globigii, MS2 bacteriophage, and staphylococcal enterotoxin B (SEB) were 10(5) cfu/mL, 10(7) pfu/mL, and 10 ng/mL, respectively. The array biosensor also analyzed multiple samples simultaneously and detected mixtures of the different types of analytes in the multianalyte format.

Computer-controlled laser ablation: a convenient and versatile tool for micropatterning biofunctional synthetic surfaces for applications in biosensing and tissue engineering

This paper describes laser-based methods for preparing micropatterns of bioactive molecular species in self-assembled monolayers (SAMs) and micropatterns of proteins and other biological molecules immobilized on solid substrates. Applications of these micropatterned surfaces in multianalyte biosensing and tissue engineering are emphasized. The focus of the paper is on the use of a computer-controlled laser ablation system comprising a research-grade inverted optical microscope, a pulsed nitrogen-pumped dye laser emitting at 390 nm, a programmable sample stage, and the computerized control system. The laser system can be implemented in a typical biosensor or tissue culture laboratory to enable the facile and reproducible fabrication of micropatterned surfaces by several methods. Various methods for patterning are discussed with examples given and emphasis placed on (1) laser ablation in the fabrication of photolithography masks, (2) electrochemical patterning of SAMs, and (3) laser desorption of SAMs. The relative merits of each technique are discussed with respect to application in fabrication of active surfaces for biosensing and tissue culture applications.