Electromagnetic sensors for magnetic bio-detection

Magnetic bio-detection constitutes a large area of research driven by its potential to provide versatile diagnostic tools. Specific sensing technology is used depending on the applications which can be subdivided in two main groups: measuring a magnetic field from living organs and detecting magnetically labelled bio substances. The human body has some magnetic sensitivity, however small, being paramagnetic or diamagnetic. In addition, there is a further source of a magnetic field due to the neural activity which involves the movement of electric charges and gives rise to magnetic fields. In the other stream of applications, the use of magnetic labels allows the detection of various bio molecular reactions in immunoassays. It also results in a number of additional functionalities, such as transport of bio-molecules and testing or accelerating bio-molecular binding events. The magnitudes of the magnetic fields involved are very small being in the sub-nanoTesla region and their detection requires very sensitive instrumentation. We have extremely sensitive magnetic technology: SQUID magnetometer, however, the cost involved and the complex cryogenic technology present huge hurdles. The signals from the brain are at about 1 picoTesla or less but from other parts of the body (such as the eyes and the stomach) are at levels an order of magnitude larger. One of the largest signals results from the heart which is at the level of about 25pT. The detection of this level of a magnetic field does not require all the potential of SQUIDs and other high performance magnetometers can be used. Here we will discuss the potential of using as biosensors such magnetometers as fluxgate and giant magnetoimpedance (GMI) sensors. As far as the detection of magnetic labels is concerned, we will consider the advantages of the detection method based on non linear magnetization of magnetic labels through generation of high frequency harmonic spectra often referred to as magnetic particle spectral method (MPS). In all these sensors the dynamic magnetization processes are involved and we categories them as electromagnetic bio sensing platform.