Team:Freiburg/Project/Overview

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  • Building our own device

    The original measuring device we were using in collaboration with AG Roth is a really expensive machine based on rather simple physics. Therefore, we decided to build our own device in a cost-efficient variant. We performed reliable measurements with it and provide a building plan making label-free proteinarray analysis available for every future iGEM team.

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  • Communicating science

    Fast and reliable disease diagnostic is a problem of public interest. For this reason we wanted to know what people think about the idea of the DiaCHIP. Although the DiaCHIP is concerned to synthetic biology, which makes people feel rather uncomfortable according to a survey by Leopoldina (national academy of science), we obtained a lot of positive feedback.

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  • Modeling cellfree expression

    In order to optimize the DiaCHIP for future applications, we modelled the process of cell-free expression and diffusion over time. Making use of xxx parameters and xxx ordinary differential equations, we computed the size of the resulting antigen spots and identified the factors limiting cell-free expression in the DiaCHIP.

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  • Measuring our own blood

    One of the most notable results we obtained was the detection of anti-tetanus antibodies in human blood serum. Using the DiaCHIP, we were able to distinguish serum samples of a person taken before vaccination and three weeks later. As expected, antibody binding events were shown after vaccination, whereas there was no signal before.

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Project overview: The DiaCHIP

DiaCHIP_Sabi

The DiaCHIP is an innovative tool to simultaneously and differentially detect antibodies present in blood sera in response to an infectious disease. It bears the potential to greatly simplify broad band screenings, detection of autoimmune diseases and the determination of vaccination statuses. Especially in case of threatening infections accompanied by similar symptoms fast and reliable differentiation could save lives.
To account for a disease by verification of corresponding antibodies in a patient’s blood serum is a well-known and routinely used system in modern diagnostics. Thus, a simple blood sample is sufficient to perform reliable diagnostics with the DiaCHIP.
The key feature in the concept of the DiaCHIP is the combination of on-demand protein synthesis and an innovative, label-free detection method in one device. This enables to overcome challenges in storage and handling that occur with currently available tests. Additionally, diagnoses can be received faster and in a more cost-efficient way than until nowadays. Nonetheless, the whole device is so simple that it can easily be rebuilt and utilized by future iGEM teams (LINK – new device).

Step 1: Preparing the DiaCHIP by protein synthesis
Before being able to screen for antibody-antigen interactions, the antigens have to be synthesized and immobilized in a microarray arrangement. This is obtained by a copying mechanism converting a DNA template into a protein microarray by cell-free protein expression. This expression system based on a bacterial lysate prevents the need for genetically engineered organisms to produce every single antigen.
To obtain the DNA template, the respective sequences containing transcriptional and translational initiation sites, the antigen coding sequence and terminating regions have to be constructed and labeled with an amino group. An activated PDMS slide provides the basis for immobilization of the DNA by covalent binding of the amino group. Spotting the antigen coding sequences in a distinct pattern enables to retrace a detected binding event to a certain disease. The template slide is placed in close proximity to the future protein array enabling the expressed proteins to reach this other surface by diffusion. Complex chemistry ensures that target proteins are specifically immobilized on this surface, while components of the expression mix can be washed away before sample analysis.

Step 2: Measuring serum samples by iRIf
After preparation of the DiaCHIP, a patient’s serum sample can be flushed over the protein array. The binding of antibodies to the protein surface causes a minimal change in the thickness of the slide right at the corresponding antigen spot. This change can be measured without the need for a further label with an emerging method called iRIf (imaging reflectometric interference). Based on the interference of light beams reflected on different thin layers, binding events can be recorded in real-time.

After weeks of opimizing the different components of the DiaCHIP, we reveal our great results. The highlight of our project was reached with the successful detection of antibodies in our own blood!