Highly sensitive detection of labeled microparticles in blood

The Microspheres Based Detoxification system is an adsorption system, whereby microadsorbent particles with diameters of 1 to 20 mum circulate in an extracorporeal filtrate circuit. A thin-wall hollow-fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a means to detect membrane ruptures that could lead to a release of microparticles into the patient´s bloodstream. An optical detection system was developed to monitor the venous bloodstream for the presence of microparticles from the filtrate circuit. For detection purposes, we use superparamagnetic monodisperse polystyrene microparticles (diameter 2.8mum) with a covalently bound fluorescence dye. The labeled marker beads are included with the microsphere-adsorbent particles in the MDS circuit. In the case of a membrane rupture, the labeled particles would also be released into the bloodstream. By illuminating a small volume of blood at the excitation wavelength (590 nm) of the fluorescence marker, the particles can be detected by their emission light at 620 nm. The detector sensitivity is increased by collecting the ferromagnetic and fluorescently labeled microparticles using a magnetic trap. In vitro experiments were performed by pumping whole blood and labeled microparticles through the fluorescence detector. With an optimal trap setup, less than 2mg of labeled microparticles can be clearly detected in streaming whole blood.