An cartridge is combined with a smart device which is capable of communicating with a network to perform a portable, fast, field assay of a small sample biological analyte. A closed microfluidic circuit for mixes the analyte with a buffer with functionalized magnetic beads capable of being specifically combined with the analyte. A detector communicates with the microfluidic circuit in which the mixed analyte, buffer and combined functionalized magnetic beads are sensed. A microcontroller is coupled to detector for controlling the detector and for data processing an output assay signal from the detector. A user interface communicates with the microcontroller for providing user input and for providing user output through the smart device to the network.