The DiaCHIP: Overview

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 successful 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 a short time bears the potential to save lives.
Spotting diseases by detecting correspondent antibodies in a patient's serum is an established method in modern diagnostics. The DiaCHIP makes it possible to screen for multiple specific antibodies simply using a drop of blood.
The key feature of the DiaCHIP concept is the combination of on-demand protein synthesis and a novel method of label-free detection packed into 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
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 are proud to present our results. We reached the highlight of our project with the successful detection of antibodies in our own blood!