Team:Freiburg/Design
Diagnostics Today
Limitations of Currently Available (Immunodiagnostic) Tests
Even though current diagnostic methods provide reliable information on a broad range of diseases, there are still applications where current methods suffer from various restrictions. The commonly used ELISA only provides a limited capacity for multiplexing (as only one interaction per well may be detected) and takes at least several hours and large amounts of sample as well as antibodies (0.05-1.2 µg antibody per well 1)). Lateral flow tests are much faster but can only detect one molecule of interest and are known to perform poorly in terms of sensitivity. Miniaturized immunoassays (microarrays) combined with microfluidic bioanalysis have been shown to have a great potential regarding future diagnostics 2). Yet, immunoassays based on peptides suffer from poor peptide purity (and thus high unspecificity), instability and storage issues. Furthermore, the diagnostics by microarray based immunoassays is scarcely used for rare disease cases after conventional ELISA tests have proven no result. In contrast, a fast diagnosis is essential for an immediate onset of an appropriate treatment, that can be critical for the patients' health and life. Moreover, improved diagnostics are not only required regarding the health of a patient: 70% of healthcare expenses 3) are linked to diagnostic tests. Therefore, improvements in diagnostic technologies have the potential to drastically reduce the overall healthcare costs while increasing health as such. Diagnostic tests are usually developed for the utilization in air-conditioned laboratories with refrigerated storage of chemicals, a constant supply of calibrators and reagents, highly trained personal and rapid transportation of samples. This setting is not available for most developing countries 4). Thus, most of the substantial progress that has been achieved in the public health and POC sector has only been advantageous to the more developed part of the world. According to the WHO 5) 2.5 out of 6 billion people lack basic sanitation, 2 billions do not have access to electricity and more than 1 billion lack basic healthcare services and clean drinking water. Moreover, 50% of all deaths in the most impoverished developing countries are a result of infectious diseases, whereas in the wealthiest developed countries this concerns less than 5%. Therefore, transforming existing technologies into mobile applications, robust and sensitive enough for the use outside of specified laboratories, may be a huge leap forward to improving general health all over the world. Outbreaks and spreading of potential epidemic diseases or sexually transmitted infections can be controlled by rapid diagnosis and appropriate treatment 5).
A need for such technologies is urgent: 500 million people between the age of 15 to 49 are infected with curable sexually transmitted infections like chlamydia, gonorrhea, syphilis or trichomoniasis each year 6)! However, the currently available infrastructure for diagnosis of infectious diseases often prove to be too slow and expansive to be practicable for third world countries. For example the identification of pathogens of an infectious diarrhea takes 2-4 days – even in the best developed-world laboratory! 7).
To be used in low-resource settings future diagnostic methods have to obtain certain properties as outlined below:
- Rapidity/Speed - a fast diagnosis reduces the time until the beginning of treatment, preventing the spread of epidemic diseases and reducing the severity of a disease.
- Simplicity - the necessary handling should be as easy as possible.
- Low-costs - POC diagnostics need to be affordable for the utility in developing countries.
- Clearness - The output of POC tests needs the clarity and simplicity as a yes/no answer.
- Easy to store under extreme conditions - As defined conditions may not be required, the device has to be stable under extreme conditions, with temperatures ranging from 10 to 40°C (50 to 104°F).
- Multiplexed test - Covering a broad spectrum of possible diseases, ideally in one device, allows for differential diagnosis even in the case of different diseases with similar symptoms.
How can our DiaCHIP contribute to the solution to these problems?
Our approach basically combines three promising techniques in one DiaCHIP device, offering a great potential to improve future diagnostics. Miniaturized immunoassays combined with microfluidics: Miniaturized immunoassays enable for immense multiplexing. By immobilizing hundreds of different antigens, it is possible to screen a patient’s sample for hundreds of potential antibodies and related diseases. With small volumes of reagents and samples, a rapid delivery of results with fast turnover times and enormous multiplexing is possible with microfluidic based LOC systems. Microarray Copying (generate proteins from DNA templates): Storing and handling problems of conventional peptide based microarrays are circumvented by directly producing our protein array from a DNA array via cell-free expression. As DNA is stable within a large range of temperatures, pH values and other environmental conditions, it proves to be the ideal molecule for storing protein information. This allows us to offer different combinations of antigens, providing the optimal detection system for most needs and producing them on demand. iRIf detection method: This emerging detection method enables a fast, sensitive and label free detection of binding processes. Binding of the serum originated, antibody can be detected directly, omitting the incubation of the sample with a second detection antibody, thus making the detecting cheaper and faster. Nevertheless, the signal can be further amplified with a secondary antibody, if needed or specificity of binding remains unclear. But even then only this second antibody without any fluorescent or enzymatic labeling is needed.
If you want to read more about today's diagnostic methods, click here.
References
