Electron transfer from Proteus vulgaris to a covalently assembled, single walled carbon nanotube electrode functionalised with osmium bipyridine complex: application to a whole cell biosensor.

We report the fabrication and use of electrodes constructed from single walled carbon nanotubes (SWCNTs) chemically assembled on a carbon surface and functionalised with an osmium(II) bipyridine complex (Osbpy). The ability of the electrodes to transduce biologically generated currents from Proteus vulgaris has been established. Our investigations show that there are two contributions to the current: one from electroactive species secreted into solution and another from cell redox sites. The modified electrode can be used to monitor cell metabolism, thereby acting as a whole cell biosensor. The biosensor was used in a 1-h assay to investigate the toxicity of ethanol, sodium azide and the antibiotic ampicillin and gave quantitative data that were closely correlated with standard cell plate viability assays. The results provide proof of principle that the whole cell biosensor could be used for high throughput screening of antimicrobial activity. One of the modified electrodes was used for approximately 1000 measurements over four months demonstrating the robustness of the system.