Eddy-current sensing of superparamagnetic nanoparticles with spiral-like copper circuits

• Detection of magnetic nanoparticles with copper printed wiring boards is reported.
• The detection is based on the superparamagnetic character of the nanoparticles.
• The response of sensor is enhanced by a factor 150 with respect to previous reports.
• The improvement of the response is due to skin and proximity effects.

In the late years, magnetic nanoparticles are being increasingly used for biological analysis due to their good performance in both magnetic separation and magnetic detection. Recently, a novel method of superparamagnetic particle detection inspired on eddy current sensing was reported. An increase of the impedance of an RF-current carrying copper conductor is induced by the nanoparticles, whose origin relies on their superparamagnetic behaviour. The detection method joins large sensitivity, low-cost and simplicity which make it highly promising for biodetection as well as for particle characterisation. With the double aim of deepening in the physical origin of this particular kind of electromagnetic induction and of improving the sensing performance, this paper studies the detection of superparamagnetic iron oxide nanoparticles with copper-based printed wiring boards. As a result, the analysis of different geometries has lead to designs which spectacularly enhance the sensitivity respect to previous reports.