Ultra-wide detectable concentration range of GMR biosensors using Fe3O4 microspheres

Exchange-biased GMR sensors were employed for biodetection using a DC in-plane measuring method and a magnetic label of Fe3O4 microspheres. It was revealed that an ultra-wide concentration span covering five orders from 10 ng/mL to 1000 mu g/mL was achieved in a home-made biodetection device. The concentration x dependence of output voltage difference vertical bar Delta V vertical bar between with and without magnetic labels, exhibits nonlinear futures, which undergoes two functions depending on the concentration region. For the low concentration region from 10 ng/mL to 10 mu g/mL, a logarithmic relation of vertical bar Delta V vertical bar = 26.3Igx+91.4 fits well, while for the high concentration region, a negative exponential function of vertical bar Delta V vertical bar=3113(1-e(-x/250)) describes the vertical bar Delta V vertical bar similar to x relation better. For the former, the coffee ring effect, formed during the solvent evaporation, was considered as the main reason for the nonlinear relation. While for the latter with high concentration, the overlap among the particles and the enhanced interaction of the magnetic dipole were responsible for the nonlinear vertical bar Delta V vertical bar similar to x relationship. Moreover, the calculated detectable concentration limit is agreed well with the experimental data. (C) 2016 Elsevier B.V. All rights reserved.