Measurement of the concentration of magnetic nanoparticles in a fluid using a giant magnetoresistance sensor with a trench

A highly sensitive giant magnetoresistance sensor with a micropatterned trench is described for the measurement of the concentration of magnetic nanoparticles in a fluid, within a few micrometers from its surface. The measurement is based on an analysis of the time-dependent development of the signal. A comparison of the experimental data with the results of model-calculations reveals the significant roles played by diffusion and sedimentation in the fluid. These results are relevant for the development of reliable biological tests based on magnetic biosensors.