Electrochemical As(III) whole-cell based biochip sensor

• In situ electrochemical read-out of a whole-cell bacterial bioreporter assay for the quantification of arsenic is presented.
• High sensitivity (LOD=0.8 ppb) and fast response time were achieved.
• High-throughput analyses were obtained by using a portable microchip containing 16 independent electrochemical cells.
• The method was validated on several groundwater samples coming from Swiss and Romanian mountains.

The development of a whole-cell based sensor for arsenite detection coupling biological engineering and electrochemical techniques is presented. This strategy takes advantage of the natural Escherichia coli resistance mechanism against toxic arsenic species, such as arsenite, which consists of the selective intracellular recognition of arsenite and its pumping out from the cell. A whole-cell based biosensor can be produced by coupling the intracellular recognition of arsenite to the generation of an electrochemical signal. Hereto, E. coli was equipped with a genetic circuit in which synthesis of beta-galactosidase is under control of the arsenite-derepressable arsR-promoter. The E. coli reporter strain was filled in a microchip containing 16 independent electrochemical cells (i.e. two-electrode cell), which was then employed for analysis of tap and groundwater samples. The developed arsenic-sensitive electrochemical biochip is easy to use and outperforms state-of-the-art bacterial bioreporters assays specifically in its simplicity and response time, while keeping a very good limit of detection in tap water, i.e. 0.8 ppb. Additionally, a very good linear response in the ranges of concentration tested (0.94 ppb to 3.75 ppb, R2=0.9975 and 3.75 ppb to 30 ppb, R2=0.9991) was obtained, complying perfectly with the acceptable arsenic concentration limits defined by the World Health Organization for drinking water samples (i.e. 10 ppb). Therefore, the proposed assay provides a very good alternative for the portable quantification of As (III) in water as corroborated by the analysis of natural groundwater samples from Swiss mountains, which showed a very good agreement with the results obtained by atomic absorption spectroscopy