Abstract: A biosensor system for the detection of particles includes a biosensor cartridge having a sensor surface. A biosensor magnet assembly is disposed on one side of the cartridge for generating a magnetic field effective at the cartridge and the sensor surface. The biosensor magnet assembly includes at least two magnetic sub-units separated by a gap. A first optical detection system detects the particles arranged at the same side of the cartridge as the magnet assembly. The magnet assembly and the first optical sensor are disposed such that the optical detection is accomplished through the gap of the magnet assembly.

Abstract: The invention relates to a substance determining apparatus (19) for determining a substance within a fluid. A location event determination unit (34) determines location events indicating that a particle, which may have attached the substance, is located in a sensing region and a property of the location events from the sensing signal generated by sensing the sensing region. A location events selection unit (70) selects a part of the location events having a property in a predefined property range, and a substance determination unit (40) determines the substance within the fluid (3) based on the selected part of the location events. This allows tuning the determination of the substance within the fluid to a desired property range, which can relate to a desired kind of bound particles, thereby reducing the influence of unwanted effects on the determination of the substance and, thus, improving the determination accuracy.