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 succesful 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 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!