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.
We describe a biosensing module in which live bacteria, genetically “tailored” to respond to the presence of a specific target material, constitute the core sensing element, reporting their response by bioluminescence. The module is constructed of two channels: an ‘induced’ channel that measures the bioluminescent light emitted by bacteria exposed to the inspected area, and a ‘reference’ channel that measures in parallel the bioluminescent light emitted spontaneously by bacteria of the same batch. This enables to overcome signal variations generated by different batches of bacteria, and due to varying environmental operating conditions. A special low-noise optoelectronic circuit was constructed to detect the bioluminescence emitted by the bacteria in both channels. The bacteria are encapsulated in polymer beads that also contain nutrients and water, enabling long-term maintenance-free operation. The beads are packaged in special cassettes at the bottom of the module, so that the induced channel cassette is in direct contact with the ground underneath the module, whereas the reference channel cassette is isolated from the ground. The module contains, in addition, a digital signal processing unit, and a wireless communication unit. The module is designed to operate outdoors as an autonomous network element designed for large scale in-situ deployment. The module described herein was developed for the detection of buried landmines, by sensing the presence of 2,4-dinitrotoluene (DNT) vapors released by the mine, accumulating in the ground above it. Detection of DNT in the sub-ppm range is demonstrated.
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