Bioactivated PDMS microchannel evaluated as sensor for human CD4⁺ cells-The concept of a point-of-care method for HIV monitoring

Up to today, the number of CD4⁺ lymphocytes remains the most important biological marker to determine the clinical stage of an HIV-infection. Analysis by flow cytometry, the standard method used today, is unsuitable in many developing countries, because of high costs involved and practical inconveniences. We here present the concept of an inexpensive PDMS-based point-of-care device for CD4-count. A simple fluorescence microscope for stained leucocytes counting is the only detection equipment needed. The biosensor surface consists of an initial heparin-based coating that adds hydrophilicity and thromboresistance to the PDMS material. The specific capturing chemistry is based on an avidin/biotin-antibody surface architecture. Pure capillary forces draw whole blood, as well as rinsing buffer, into the biosensor channel, minimizing the need of external equipment. Detection of the captured cells was performed by fluorescence imaging of HOECHST (stains cell nuclei) and CD3-FITC signals. It was shown that the non-specific adsorption of CD4^- leucocytes was minimal to none, and the detection could therefore be done by only counting the easy identifiable HOECHST⁺ cells. Characterization of the biosensor coating process was additionally performed with the quartz crystal microbalance-dissipation technique.