  We report integration of an InAs quantum well micro-Hall sensor with
microfluidics and real-time detection of moving superparamagnetic beads for
biological applications. The detected positive and negative signals correspond
to beads moving within and around the Hall cross area respectively. Relative
magnitudes and polarities of the signals measured for a random distribution of
immobilized beads over the sensor are in good agreement with calculated values
and explain consistently the dynamic signal shape. The fast sensor response and
its high sensitivity to off-cross area beads demonstrate its capability for
dynamic detection of biomolecules and long-range monitoring of non-specific
binding events.
