Voltammetric detection and profiling of isoprenoid quinones hydrophobically transferred from bacterial cells.

We have developed a novel bacterial detection technique by desiccating a bacterial suspension deposited on an electrode. It was also found that the use of an indium-tin-oxide (ITO) electrode dramatically improved the resolution of the voltammogram, allowing us to observe two pairs of redox peaks, each assigned to the adsorption of isoprenoid ubiquinone (UQn) and menaquinone (MKn), which were present in the bacterial cell envelopes, giving midpeak potentials of -0.015 and -0.25 V versus Ag|AgCl|saturated KCl| at pH 7.0, respectively. Most of the microorganisms classified in both the Gram-negative and -positive bacteria gave well-defined redox peaks, demonstrating that this procedure made the detection of the quinones possible without solvent extraction. It has been demonstrated that the present technique can be used not only for the detection of bacteria, but also for profiling of the isoprenoid quinones, which play important roles in electron and proton transfer in microorganisms. In this respect, the present technique provides a much more straightforward way than the solvent extraction in that one sample can be prepared in 1 min by heat evaporation of a suspension containing the targeted bacteria, which has been applied on the ITO electrode.

Electrochemical evaluation of poly(3,4-ethylenedioxythiophene) films doped with bacteria based on viability analysis.

To immobilize viable bacteria on an electrode, we present a novel and straightforward technique that relies on the negative ζ-potentials of bacteria for insertion into conducting polymers as dopants. In the present study, we conducted an electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with various gram-negative bacteria, including Pseudomonas aeruginosa, Escherichia coli, and Shewanella oneidensis. The PEDOT film doped with bacteria indicated a typical redox response, high conductivity, and electrochemical stability. Fluorescence microscopy confirmed that approximately 90% of the bacteria incorporated into the PEDOT film at >0.5 µm in thickness were viable.

Nanoantennas as biomarkers for bacterial detection.

Understanding the biology of bacteria is critical for exploiting their beneficial properties and for preventing and treating bacterial diseases. Nanobioscience is an area that has recently seen major scientific progress. Here, we demonstrate that a raspberry-shaped nanostructure with a high density of gold nanoparticles acts like an excellent antenna due to its optical properties, which permit sensitive detection and analysis of bacterial cells. By using antibodies, these nanoantennas can be engineered to recognize only specific bacterial species. This system provides a new technique that will allow for more sensitive detection of specific bacteria.

Development of an observation platform for bacterial activity using polypyrrole films doped with bacteria.

In our study, various bacteria, including Gram-negative (Pseudomonas aeruginosa, Escherichia coli, Acinetobacter calcoaceticus, Serratia marcescens, Shewanella oneidensis) and Gram-positive (Bacillus subtilis) bacteria, were straightforwardly immobilized into the conducting polymers (CPs) by electrochemical deposition. The doping state of bacteria in the polymer films (polypyrrole and poly(3,4-ethylenedioxythiophene)) varied according to the polymerization conditions. The viability of bacteria in the polymers and of those adsorbed on various substrates was evaluated. The activity of bacteria doped on the polymer film was evaluated by cyclic voltammetry in a thin-layer cell.