Quantitative chemical sensing employing bioluminescent bacteria

We present a methodology for quantitative sensing of the contents of a target material (TM) in a given sample which employs biosensing bioluminescent bacteria. These bacteria are genetically engineered to respond to the presence of a specific TM in their microenvironment by producing bioluminescence. Herein, we extend this methodology to include quantitative sensing of the TM content in the inspected sample by exploiting the dependence of the bioluminescence produced by the bacteria on the content of the TM in the inspected sample. However, employing bacteria as precise measurement devices is inherently problematic, as the signal they produce varies between different batches of bacteria, and changes as the batch ages. Moreover, As the methodology is designed for outdoor operation, the sensitivity of the bacteria response to changes in the environmental conditions needs to be taken into account. These hurdles are overcome in a special optoelectronic sensor which measures in parallel the responses produced by the inspected sample, and a standard sample containing a known quantity of the TM. Both measurements are conducted by identical sensing channels using bacteria from the same batch, and under the same environmental conditions. The "standard ratio" (SR) defined as the ratio between the maximum responses of the inspected sample and the standard sample was found to be independent of the batch and environmental conditions. A calibration curve of the SR vs. the TM concentration in a set of preprepared samples is used to gauge SR at the sensor output to the TM concentration in the inspected sample.