Flow cytometry becomes increasingly important for clinical diagnostics and medical research, while state-of-the-art instruments remain bulky and require expensive components. Measurements are taken within flow cell by moving cells in liquid solution through an excitation spot and detecting the emanating fluorescent light. The optical setup requires lasers to have sufficient excitation power and sensitive photo multiplier tubes or avalanche photo diodes for detection. We will show a compact and rugged system using a novel spatially modulated emission technique. It consists of a microfluidic chip for the fluidic handling, an LED or laser diode for excitation, a spatial mask and a simple PIN or avalanche photodetector. No critical alignment between these components is necessary. The relative movement of the particle with respect to the spatially patterned mask enables sophisticated signal processing for reliable particle detection. This concept relies on a relatively large excitation area to increase the total flux of fluorescence light. Despite the large excitation area the mask patterning enables a high spatial resolution in the micrometer range. This allows independently detecting and characterizing particles with a distance down to object size. In addition this concept is intrinsically tolerant to background fluorescence originating from unbound dyes in solution, fluorescing components of the chamber and contaminants. These features will ultimately allow for simple sample preparation and reduced amount of consumables. The presented platform enables a cheap and robust on-chip flow cytometer for point-of-care applications as well as miniaturized high performance flow cytometers. We will show experimental results demonstrating the following achievements: - Detection of tagged CD4-cells (dye: PE) at flow speeds up to 1m/s (excitation: 535nm) - CD4 count in whole blood for monitoring the immune status of HIV infected persons - Detection of cells via native fluorescence (excitation 266nm, fluorescence 340nm) - Characterization of individual beads (diameter 6um) down to a particle distance of 10um - Detection of 0.6um fluorescent beads at a excitation power density below 5W/cm2.
Citation
Bassler, M.; Kiesel, P.; Beck, M.; Schmidt, O.; Hegyi, A.; Buergel, T.; Johnson, N. M. A novel concept for on-chip flow cytometry with improved signal-to-noise-ratio and "alignment-free" optics. XXIV International Congress of the International Society for Analytical Cytometry; 2008 May 17-21; Budapest, Hungary.
