Figure 3. Magnetic susceptometer biosensor.
(a) A quadrature detector was developed to sense alternating current (AC) magnetic susceptibility in solution. PLL, phase-locked loop. (b) The peak in the magnetic susceptibility shifts with particle size. The magnetic responses of two differently sized MNPs were measured (red, 25-nm core; blue, 50-nm core). This information was used to distinguish the composition in the mixture (green). Reprinted with permission from Ref. 56. Copyright 2011 IOP Publishing Ltd.