In the past few years, magnetic biosensors have received tons of interest as a promising candidate for the realization of highly sensitive biosensors. In this approach, the traditional yet classic label like fluorescence tag, is replaced by a super-paramagnetic bead, which can be detected using magnetic beads and magneto-resistive sensors. Apart from an increased sensitivity, magnetic biosensors also show the unique ability of modulating these labels by applying controlled magnetic force. By immobilizing bio-molecules onto the particle's surface, this results in a number of additional functionalities, such as transport of bio-molecules to a specific location on the chip; on-chip magnetic immuno-separation of bio-molecules and cells; and, testing or accelerating bio-molecular binding events.
Recently, the main focus was on the development of magneto-resistive biosensors on the purpose of increasing the sensitivity by combining detection and manipulation of magnetic beads. For magneto-resistive sensors, the distance of bound magnetic beads relative to the sensor location shows a clear dependence on the signal. Based on this phenomenon, many companies are exploring the ability to enhance the sensitivity and specificity via active guiding of magnetic beads using on-chip generated magnetic forces. First, a sandwich assay is build up on the device surface, followed by labeling with magnetic beads. Then, the bound magnetic beads are released and transported to that position that theoretically gives rise to the maximal signal, ensuring the most sensitive detection. In order to enhance the sensitivity, specificity and dynamic range for the detection of proteins, the impact of the surface chemistry, assay, type of particles and release mechanism has been fully evaluated.