Diagnostics Today

Limitations of Currently Available (Immunodiagnostic) Tests

Current diagnostic methods 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 - time is a crucial point in diagnostics, to prevent e.g. the spreading of a highly contagious disease. For a patient fast detection can mean the difference between live and death.


• Simplicity - the necessary handling should be as easy as possible.


• Low-cost - point of care diagnostics need to be affordable especially when considering usage in developing countries.


• Unambiguity - the output of point of care tests needs the clarity and simplicity of a yes/no answer.


• Storage under sub-optimal conditions - As optimal storage conditions cannot be always guaranteed, the device and its components have to be working reliably under harsh conditions, with temperatures ranging from 10°C to 40°C (50°F to 104°F).


• Multiplexed testing - Covering a broad spectrum of possible diseases (ideally integrated into one test run) allows for a differential diagnosis even in the case of different diseases with similar symptoms.

The commonly used ELISA while providing reliable results, 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 few molecules 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 great 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 point of care 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 accounts for less than 5% of deaths.

Therefore, transforming existing technologies into mobile applications is a leap forward to improve access to diagnostic tools all over the world. These applications should be robust yet 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 becomes obvious when considering 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 the DiaCHIP contribute to the solution to these problems?

Our approach basically combines three promising techniques in one DiaCHIP device, offering great potential to improve future diagnostics.

Miniaturized immunoassays enable 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 short turnover times and enormous multiplexing is possible with microfluidic based lab-on-a-chip systems.

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 circumventing protein purification and storage.

This emerging detection method allows 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. The use of specific secondary antibodies allows for differentiation between an acute disease and an old immunization.

If you want to read more about today's diagnostic methods, click here.

We also considered and address potential ethical concerns of the DiaCHIP in a dedicated section, read more about it here.