A PDMS-based disposable microfluidic sensor for CD4+ lymphocyte counting.

A refined sensor for CD4+ lymphocyte count was developed and evaluated by comparison to flow cytometry. The micropillar structured sensor surface was cast in PDMS polymer and surface modified to gain biocompatibility and CD4-cell capturing properties. The sensor works by pure capillary action and sample filling and rinsing is performed without external equipment. Whole blood samples showed acceptable agreement (79%) with flow cytometry, however when diluting the blood in PBS buffer we discovered that a larger number of cells were drawn into the sensor microchannel compared to the initial sample, explained by enhanced shear-induced cell migration. Using plasma or PBS with glycerol or albumin additives as diluting media greatly influenced this cell behavior, showing the importance of controlling the dilution media when working with devices based on capillary filling. The sensors need to be further tested with blood samples with lower CD4-counts (<500 cells/μl), which are clinically relevant.