Humans have been polluting water with natural products for hundreds of years. However, during the last decennia the amount of unnatural chemicals that are being produced, used and carelessly disposed of, has been increasing rapidly. A substantial part of these chemicals introduced in our water supplies are derived from pharmaceuticals.
We focussed on the one pharmaceutical contaminant that is associated with current day lifestyle, Selective Serotonin Reuptake Inhibitors (SSRI), commonly known as antidepressants. After leaving the human body, the remainder of the medicine ends up in the sewage system and is not broken down readily by the sewage treatment plants, resulting in an increasing concentration in surface waters. Even in low concentrations, antidepressant waste products pose a threat to ecological systems, for example because they are still biologically active in vertebrates, changing their behaviour and fertility. Current techniques for the detection of pharmaceutical waste products are either expensive or inaccurate. An improved system is therefore needed.
Consultation of experts and stakeholders provided us with five core requirements:
- Possibility for detecting diverse compounds
- Accurate detection at different concentrations
- Clear and easily measurable detection signal
- Rapid signaling
- Low-cost system
These requirements were met by developing DeTaXion, a biodetection system that exploits the fast and highly customizable chemotaxis pathway of Escherichia coli, a bacterium that can be produced at low cost. This pathway was adapted using a three step approach to accomplish the desired biosensor. First, exchanging the ligand binding domain of the E. coli chemotaxis receptor Tar will allow the bacteria to recognize diverse pharmaceutical compounds. We have already developed and implemented a validation assay to assess the functionality of the receptor. Next, methylation sites can be customized to extend the detection range of the DeTaXion biosensor which allows accurate pollutant detection at different concentration ranges. We have mathematically modelled the effect of changes in the methylation sites to assess the effect on the detection range. Finally, a bioluminescence resonance energy transfer (BRET) pair was introduced to generate an easily detectable and quantifiable signal.
The mutated E. coli was designed to be integrated into an easily usable hand-held device. Our design includes various features to solve safety, regulatory, and technical issues. Ultimately, the product will enable low-cost, rapid, and accurate detection of pharmaceutical waste products for diverse ligands and at a range of concentrations. It can be used as a stand-alone product to continuously monitor a water supply, or to complement traditional chemical analyses, thereby improving the detection of pharmaceutical waste products in aquatic systems and contribute to a cleaner environment.