Magnetic particles are often used to transport and/or separate biomolecules such as DNA or proteins. These particles have biochemically functionalized surfaces and are used as markers in analytical biotechnology and medical technology. In order to chronologically integrate the signal of several particles, they must be magnetized and be as consistently oriented as possible. This has previously been done by generating an external magnetic field.

This invention describes a magnetic field sensor for detecting these magnetic particles in fluids. The system’s unique feature is that it does not utilize extra conductive tracks to generate the magnetic field, rather it generates the field itself by passing current through the magnetic sensor layer. The sensor system works by generating a signal at double the frequency almost entirely from the effect of the stray field created by the magnetized particles on the sensor layer. The benefit of this detection method is increased measuring sensitivity, since interference caused by, e.g., capacitive couplings between the sensor system and electrically conductive connections do not contribute to the signal at double the frequency.