Step 1: Preparing the DiaCHIP by protein synthesis
Prior to screening for antibody-antigen interactions, the antigens have to be synthesized and immobilized in a microarray set-up. The DiaCHIP facilitates this process by a copying 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 redundant.
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 silicone 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. We established a surface for specific immobilization of the target proteins. Thus, components of the expression mix can be washed away and do not hinder the analysis of the actual sample.

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