Virtually all commercial flow cytometers rely on optical interaction with the bio-particles for characterization, through fluorescence, scattering, or absorption processes. And all use the same basic optical configuration, namely, intense illumination of the bio-particle as it speeds through a highly localized spot, which generally involves a complex arrangement of optics (e.g., lenses, mirrors, apertures, and filters). This highly focused beam of light is required to achieve usable sensitivity since the signal is proportional to the photon flux density. While such instruments are extensively used in research and clinical laboratories, they do not meet the challenging practical requirements for point-of-care (POC) diagnostics in resource-limited applications, such as CD4 monitoring which is required for proper treatment of HIV infected persons in resource-limited settings. In this presentation we will describe and illustrate a fundamentally new design of the optical detection system that delivers high effective sensitivity (i.e., high signal-to-noise discrimination) without complex optics or bulky, expensive light sources to enable a flow cytometer that combines high performance, robustness, compactness, low cost, and ease of use. The enabling innovation is termed spatially modulated emission/excitation and involves relative movement between a fluorescing bio-particle and a patterned environment. This produces a time-modulated signal that is analyzed with real-time correlation techniques. The advantage is high discrimination of the particle signal from background noise. In addition the technique allows distinguishing the signals from closely spaced particles. The cost benefit arises from the ability to replace expensive, bulky components with inexpensive ones that can be readily integrated on a fluidic chip and by eliminating the need for sophisticated optics and critical optical alignment. Potential examples include light emitting diodes for excitation and PIN diodes for photo-detection. The technology will be demonstrated with characterization of individual fluorescent beads (diameters: 6m, 2m and 0.6m), detection of tagged CD4 cells, and CD4 counting in whole blood.
Johnson, N. M.; Kiesel, P.; Bassler, M.; Beck, M. Spatially modulated emission for point-of-care flow cytometer. Fall MRS Meeting, Symposium AA: Materials for Optical Sensors in Biomedical Applications; 2008 Dec 1-5; Boston, MA USA