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Revision as of 04:03, 17 September 2015
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The DiaCHIP : Overview
The DiaCHIP is an innovative tool to screen for a broad range of antibodies present in blood serum within a single test. Antibodies indicate an immune response against an infection or a successful vaccination. Especially the ability to differentiate between life threatening diseases and mild infections within a short time bears the potential to save lives. The DiaCHIP makes it possible to screen for multiple specific antibodies simply using a drop of blood.
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.
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).
After cell-free expression not only our desired antigens are present within the chamber, but also all other components of the cell-free mix like ribosomes, polymerases or amino acids (figure 3). All these components would bind unspecifically to an activated glass slide, thereby disturbing the binding of the antigens. We designed our DNA constructs in a way that each antigen can easily be fused to specific tags that enable targeted immobilization on a specific surface. Testing different tag systems, we found the Ni-NTA-His-tag system working best for our purposes. A basic protocol for this specific surface was optimized by ourselves to reduce unspecific binding.
After preparation of the DiaCHIP, a patient’s serum sample can be flushed over the protein array using the same microfluidic system. The binding of antibodies to the corresponding 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 using a novel technique called iRIf iRIf (imaging Reflectometric Interference) without the need for further labeling (HIER SCHON REF?). Its core components are a camera, an LED and a few lenses. See how we reconstructed the system in a low-budget device.
When illustrating the basic principle of the DiaCHIP, we mainly looked at it from the side. Now it is time to explore our results and see what we actually achieved. Therefore, it is important to have in mind that you are observing the chip from the camera's position, so basically from the top (figure 6). This persepective remains the same in all the iRIf measurements we are showing in the results section.
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!