The DiaCHIP is an innovative tool to screen for a broad range of antibodies present in serum. Antibodies can be an indicator for an immune response towards an infection or a succesfull vaccination. Antibodies also play a role in the diagnosis of autoimmune diseases. Especially the ability to differentiate between life threatening diseases and a mild infection within minutes bears the potential to save lifes.
Spotting diseases by detecting correspondent antibodies in a patient's serum is an established method in modern diagnostics. The DiaCHIP makes this possible using a single blood sample.
The key feature of the DiaCHIP concept is the combination of on-demand protein synthesis and a novel method of label-free detection packed in one device. The idea is to overcome challenges commonly found in protein array production and preservation. In addition results can be obtained in a time- and cost-efficient manner; with a device simple enough to be rebuilt by future iGEM teams. (LINK – new device).

Step 1: Preparing the DiaCHIP by protein synthesis
Pior to screening for antibody-antigen interactions, the antigens have to be synthesized and immobilized in a microarray set-up. Facilitated by a copy mechanism, which converts a DNA template into a protein microarray by cell-free protein expression. This expression system based on a bacterial lysate makes the need for genetically engineered organisms to produce each single antigen redudant.
In order to collect the DNA templates, 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!