Figure 1: The DiaCHIP is based on antigenic peptides derived from viruses and bacteria.DNA is immobilized on a silicone slide. These sequences are coding for antigens specific for several pathogens. The antigens are expressed by cell-free expression and immobilized on the glass slide.

The aim of our DiaCHIP is to screen simultaneously for hundreds of different infectious diseases. We based our system on the detection of antibodies specifically interacting with antigens derived from viruses and bacteria (figure 1). If you get in contact with one of these pathogens your immune system is producing antibodies. These are binding to the corresponding antigen which can be detected with our the DiaCHIP. Our approach is based on two components: a silicone slide where DNA coding for distinct antigenic peptides is immobilized and a glass slide with a specific surface for the binding of the expressed antigens. Both are the size of a microscopy slide and form a microfluidic chamber. By adding blood of a patient, antibodies that might be present in the sample due to a disease bind to the antigens.

Figure 2: The expression of our antigens is achieved by our cell-free expression mix. This mix is based on a bacterial lysate and contains all components required for transcription and translation of the DNA sequences.

To enable the production of a protein array consisting of multiple antigens on demand, their expression is mediated by cell-free expression from a template DNA array. This expression system based on a bacterial lysate makes the need for genetically engineered organisms to produce every single antigen redundant. The protein array is produced by flushing our cell-free expression mix through the microfluidic setup. Expressing the antigens from the DNA template, the protein array is adaptable to individual requirements exhibiting the same pattern. Our system is made up of two slides enabling the antigens to be immobilized on the opposite of the microfluidic chamber (figure 2).

Figure 3: Specific glass surface.Proteins of the cell-free mix could bind unspecifically to the surface. Therefore we established a specific surface, therefore only target proteins could bind.

After the cell-free expression not only our desired antigens are present within the chamber, but also all other components of the cell-free mix (figure 3). All these proteins would bind unspecifically, disturbing the binding of the antigens. Therefore, we designed our DNA constructs in a way that each antigen can easily be fused to tags that can bind to a specific surface. The specific surface is established by ourselves.

Figure 4: Optical detection method.It mainly consists of a camera and a LED. The high-tech method is called iRIf (imaging Reflectometric Interference). Antigen-Antibody interaction can be detected label-free and in real-time. A minimal change in the thickness of the layer on the slide right at the corresponding antigen spot can be detected, which leads to an optical output.

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 layer on the slide right at the corresponding antigen spot. This binding can be detected label-free and in real-time. The measurement without the need for a further label is called iRIf (imaging Reflectometric Interference) (HIER SCHON REF?). It mainly consists of a camera and an LED. See how we rebuilt our own low-budget device.

Figure 5: Illustration of the perspective during a measurement.

To give you a visual impression of how such a measurement looks like we switch perspectives and look at the chip from the top (figure 6). In all our actual measurement you will have this perspective.

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!