Team:Bielefeld-CeBiTec/Description
Project description
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Biosensors can be used to detect toxic substances in a highly specific and sensitive manner. Furthermore, they can be cheaper and easier to handle than conventional detection methods. For this reason, they are a field of active research and a popular topic in the iGEM competition. Most of these biosensors make use of living microorganisms, which raises a number of problems. Among them are legal issues and safety concerns, as it must be prevented that genetically modified organisms are released into the environment. Moreover, these sensors are often not very user-friendly, as they have a limited shelf life and their application outside the laboratory is complicated. In order to solve these problems and thus make biosensors applicable in everyday life, we developed cell-free biosensors that can be used as paper-based test strips.
Our principal approach towards this end relies on cell-free protein synthesis (CFPS). This system is suitable for classical repressor- or activator-based biosensors, but by carrying out the expression of the reporter protein in a cell extract, biosafety problems are prevented. Furthermore, the cell extract remains functional when it is applied onto paper, and after lyophilization, such a test strip can be stored for a long time.
We applied this system to the detection of heavy metals. Heavy metal contaminations are a global problem and a simple and cheap test would be a great help to many people. Several iGEM teams have dealt with the detection of heavy metals, so we decided to build upon this work and combine several heavy metal biosensors into one cell-free test strip. Consequently, we tested the following biosensors by previous iGEM teams and improved their characterization in the course of our project:
In addition, we tested three new biosensors...
In addition to heavy metals, we also wanted to tackle a problem that is currently very relevant in our area: The use of date rape drugs. These drugs are usually a mixture of different substances that produce narcotic effects and thus make the victim defenseless. By now, the detection of date rape drugs is only possible in retrospect in the laboratory and only in a limited time frame. There is no opportunity for checking suspicious drinks quickly and easily.
The detection of date rape drugs is very challenging, as the result needs to be obtained fast and the beverages that are analyzed often contain alcohol, which inhibits many biological reactions. Consequently, we developed a second approach towards cell-free biosensors, which takes such demands into account.
This approach, called Plasmid Repressor Interaction Assay (PRIA), utilizes the interaction between a purified repressor protein and its operator sequence.
Both CFPS and PRIA make use of fluorescence as an output signal because fluorescence is very sensitive and typically has little background signal. However, fluorescence can usually not be seen with the naked eye. Nevertheless, it is possible to easily visualize fluorescence using a smartphone and filters.
On top of that, we developed an app which automatically interprets the image and provides the user with information about the substances that were detected.
References
Pardee et al., Paper-Based Synthetic Gene Networks, Cell (2014), http://dx.doi.org/10.1016/j.cell.2014.10.004