Novel Biochip Combines Antibody Binding and Electronic Counting to Simplify Diagnosis of HIV/AIDS

A recent paper described the construction of a microchip biosensor that uses immuno-capture technology to detect sub-populations of immune leukocytes.

Investigators at the University of Illinois (Urbana-Champaign, USA) developed the small, disposable biochip in order to differentiate and count CD4+ and CD8+ T-cells, which is a key factor in diagnosing HIV/AIDS.

The prototype biochip is built around a capture chamber coated with anti-CD4+ antibodies. In addition, it has separate ports for lysing reagents and quenching buffers that preserve the leukocytes for counting by co-planar platinum microfabricated electrodes.

In practice, ten microliters of whole blood was infused into the biochip. The red cells were removed by lysis, and leukocytes were preserved using quenching buffers. The leukocytes were counted while passing over a counting device comprising co-planar platinum microfabricated electrodes on the way into the capture chamber. CD4+ T-cells were captured as they interacted with specific antibodies in the capture chamber. Leukocytes that were not captured passed out of the capture chamber and were counted again with a second counter. The difference in the respective cell counts gave the number of cells captured.

While this paper provided a comprehensive stepwise protocol to replicate the biosensor for CD4+ and CD8+ cell counts, the biochip could be adapted to enumerate other specific cell types such as somatic cells or cells from tissue or liquid biopsies. Capture of other specific cells would require immobilization of their corresponding antibodies within the capture chamber.

In clinical trials, the differential immuno-capture biochip achieved more than 90% correlation with flow cytometry for both CD4+ and CD8+ T-cells using HIV infected blood samples.

Production of the prototype biochip required approximately 24 hours. A one-time optimization of the cell capture step took six to nine hours, and the final cell counting experiment required 30 minutes to complete.

"An important diagnostic biomarker for HIV/AIDS is the absolute count of the CD4+ and CD8+ T lymphocytes in the whole blood. The current diagnostic tool—a flow cytometer—is expensive, requires large blood volume, and a trained technician to operate," said senior author Dr. Rashid Bashir, professor of bioengineering at the University of Illinois. "We have developed a microfluidic biosensor based on a differential immuno-capture electrical cell counting technology to enumerate specific cells in 20 minutes using 10 microliters of blood."

The biochip protocol was published in the March 10, 2016, online edition of the journal Nature Protocols.

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