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. 2018 Nov 7;8:16493. doi: 10.1038/s41598-018-34720-0

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© The Author(s) 2018

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Quantitative detection of superparamagnetic nanoparticles in a proof-of-concept experiment. (a) The surface is functionalized using ozone plasma then PEI in chloroform solution is applied. (b) The residue is cleaned then MNPs in hexane solution are introduced. (c) MNPs are tightly bound to PEI through ligand exchange. (d) When integrated field wires generate magnetic excitation field around GMR sensors, MNPs in close proximity produce induced field that is sensed by the GMR sensors. (e) Measured binding curves of different PEI coverages. (f–i) Scanning electron microscopic images showing MNPs bound to sensor surface. Coverage area is measured using image processing software. (j) ∆MR versus area coverage by MNPs curve. ∆MR is proportional to area coverage, which corresponds to the number of MNPs. Error bars represent one standard deviation. Dashed line represents a theoretical calculation of ∆MR from 0 to 100% coverage.