Team:Freiburg/Design
Diagnostics Today
Limitations of Currently Available (Immunodiagnostic) Tests
Current diagnostic methods might provide reliable information on a broad range of diseases, but there are still applications where current methods suffer from various restrictions.
To be used in low-resource settings future diagnostic methods should obtain the following features:
- Speed - a fast diagnosis reduces 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 in developing countries.
- Clearness - The output of POC tests needs the clarity and simplicity of a yes/no answer.
- Storage 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 a differential diagnosis even in the case of different diseases with similar symptoms.
The commonly used ELISA only provides a limited capacity for multiplexing (as only one interaction per well may be detected). It takes 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. Moreover, they 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 low specificity. As they consist of proteins, instability and storage are issues of bigger concern. Furthermore, diagnostic based on microarray immunoassays is scarcely used for rare disease cases after conventional ELISA tests have not proven a positive result. In contrast, a fast diagnosis is essential for an immediate onset of appropriate treatment, a critical factor 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 overall healthcare costs while increasing health as such. Diagnostic tests are usually developed for use 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 achieved in the public health and POC sector has only been advantageous to the more developed part of the world. POINT OF CARE
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 is a leap forward to improving general health all over the world. These applications should be robust and sensitive enough for the use outside of specified laboratories. 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 infrastructure currently available for diagnosis of infectious diseases often proves to be too slow and expensive to be practicable for third world countries. This can bee seen in the identification of pathogens of an infectious diarrhea, which takes 2-4 days – even in the best developed laboratories of the world! 7).
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. If needed, the signal can be further amplified with a secondary antibody, if specificity of binding remains unclear or the signal needs to be enhanced. This secondary antibody does also not require any fluorescent or enzymatic labeling.
If you want to read more about today's diagnostic methods, click here.
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