Hand-held flow cytometer for point of care CD4 testing

Abstract

Commercial flow cytometers are sophisticated analytical instruments extensively used in research and clinical laboratories. However, they do not meet the challenging practical requirements for point-of-care (POC) testing. PARC has demonstrated a new optical detection technique termed spatially modulated emission that delivers high signal-to-noise discrimination without precision optics to enable a flow cytometer that can combine high performance, robustness, compactness, low cost, and ease of use. The detection technique has been extensive evaluated with measurements of absolute CD4+ and percentage CD4 counts in human blood. To benchmark our system we performed a direct one-to-one comparison of measurements on the same samples with a commercial instrument (BD FACSCount) and obtained excellent agreement for both absolute CD4 and percentage CD4. We have assembled the first generation of a compact (~5x3x2 inch), single-parameter, flow cytometer based on the spatial modulation technique which uses a pin photodiode for detection rather than a PMT or APD. The prototype was assembled with off-the-shelf components (total cost of all parts <$250). The whole unit is battery powered. Measurements of the sensitivity and dynamic range of the prototype were conducted with 3.8-um ultra-rainbow calibration beads (Spherotech) and yielded a detection limit ~10^3 MEPE, which meets the needs for a wide range of bio-particle-detection applications.