{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,8]],"date-time":"2026-01-08T02:51:03Z","timestamp":1767840663901,"version":"3.49.0"},"reference-count":32,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2019,12,10]],"date-time":"2019-12-10T00:00:00Z","timestamp":1575936000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100004917","name":"Cancer Prevention and Research Institute of Texas","doi-asserted-by":"publisher","award":["CBET-1928334"],"award-info":[{"award-number":["CBET-1928334"]}],"id":[{"id":"10.13039\/100004917","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This work presents a proof-of-concept demonstration of a novel inductive transducer, the femtoMag, that can be integrated with a lateral-flow assay (LFA) to provide detection and quantification of molecular biomarkers. The femtoMag transducer is manufactured using a low-cost printed circuit board (PCB) technology and can be controlled by relatively inexpensive electronics. It allows rapid high-precision quantification of the number (or amount) of superparamagnetic nanoparticle reporters along the length of an LFA test strip. It has a detection limit of 10\u221210 emu, which is equivalent to detecting 4 ng of superparamagnetic iron oxide (Fe3O4) nanoparticles. The femtoMag was used to quantify the hCG pregnancy hormone by quantifying the number of 200 nm magnetic reporters (superparamagnetic Fe3O4 nanoparticles embedded into a polymer matrix) immuno-captured within the test line of the LFA strip. A sensitivity of 100 pg\/mL has been demonstrated. Upon further design and control electronics improvements, the sensitivity is projected to be better than 10 pg\/mL. Analysis suggests that an average of 109 hCG molecules are needed to specifically bind 107 nanoparticles in the test line. The ratio of the number of hCG molecules in the sample to the number of reporters in the test line increases monotonically from 20 to 500 as the hCG concentration increases from 0.1 ng\/mL to 10 ng\/mL. The low-cost easy-to-use femtoMag platform offers high-sensitivity\/high-precision target analyte quantification and promises to bring state-of-the-art medical diagnostic tests to the point of care.<\/jats:p>","DOI":"10.3390\/s19245433","type":"journal-article","created":{"date-parts":[[2019,12,10]],"date-time":"2019-12-10T10:52:41Z","timestamp":1575975161000},"page":"5433","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["PCB-Based Magnetometer as a Platform for Quantification of Lateral-Flow Assays"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4604-8726","authenticated-orcid":false,"given":"Mohammad","family":"Khodadadi","sequence":"first","affiliation":[{"name":"Center for Integrated Bio &amp; Nano Systems, University of Houston, Houston, TX 77204, USA"},{"name":"Materials Science &amp; Engineering, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Long","family":"Chang","sequence":"additional","affiliation":[{"name":"Center for Integrated Bio &amp; Nano Systems, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Electrical &amp; Computer Engineering, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jo\u00e3o R. C.","family":"Trabuco","sequence":"additional","affiliation":[{"name":"Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA"},{"name":"iBB-Institute for Bioengineering and Biosciences, Department of Bioengineering, Instituto Superior T\u00e9cnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Binh V.","family":"Vu","sequence":"additional","affiliation":[{"name":"Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Katerina","family":"Kourentzi","sequence":"additional","affiliation":[{"name":"Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Richard C.","family":"Willson","sequence":"additional","affiliation":[{"name":"Center for Integrated Bio &amp; Nano Systems, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2272-562X","authenticated-orcid":false,"given":"Dmitri","family":"Litvinov","sequence":"additional","affiliation":[{"name":"Center for Integrated Bio &amp; Nano Systems, University of Houston, Houston, TX 77204, USA"},{"name":"Materials Science &amp; Engineering, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Electrical &amp; Computer Engineering, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA"},{"name":"Department of Chemistry, University of Houston, Houston, TX 77204, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,12,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2023","DOI":"10.1007\/s00604-017-2176-5","article-title":"Gold nanocage-based lateral flow immunoassay for immunoglobulin G","volume":"184","author":"Yang","year":"2017","journal-title":"Mikrochim. Acta"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1874","DOI":"10.1080\/09168451.2017.1365590","article-title":"A novel multi-walled carbon nanotube-based antibody conjugate for quantitative and semi-quantitative lateral flow assays","volume":"81","author":"Sun","year":"2017","journal-title":"Biosci. Biotechnol. Biochem."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"264","DOI":"10.1016\/j.jim.2011.11.003","article-title":"Enhancement of the detection limit for lateral flow immunoassays: Evaluation and comparison of bioconjugates","volume":"375","author":"Linares","year":"2012","journal-title":"J. Immunol. Methods"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"62","DOI":"10.1016\/j.jviromet.2014.08.025","article-title":"Multi-colored immunochromatography using nanobeads for rapid and sensitive typing of seasonal influenza viruses","volume":"209","author":"Sakurai","year":"2014","journal-title":"J. Virol. Methods"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"641","DOI":"10.1373\/clinchem.2012.200360","article-title":"Lateral flow assay with near-infrared dye for multiplex detection","volume":"59","author":"Swanson","year":"2013","journal-title":"Clin. Chem."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"11684","DOI":"10.3390\/s120911684","article-title":"A Fast and Sensitive Quantitative Lateral Flow Immunoassay for Cry1Ab Based on a Novel Signal Amplification Conjugate","volume":"12","author":"Chen","year":"2012","journal-title":"Sensors"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"9481","DOI":"10.1021\/ac5012624","article-title":"Persistent luminescence strontium aluminate nanoparticles as reporters in lateral flow assays","volume":"86","author":"Paterson","year":"2014","journal-title":"Anal. Chem."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"14215","DOI":"10.1021\/am503517s","article-title":"Immunochromatographic assay for ultrasensitive detection of aflatoxin B1 in maize by highly luminescent quantum dot beads","volume":"6","author":"Ren","year":"2014","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2486","DOI":"10.1039\/C9LC00104B","article-title":"Sensitivity enhancement in lateral flow assays: A systems perspective","volume":"19","author":"Bishop","year":"2019","journal-title":"Lab Chip"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Sch\u00fcler, D. (2007). Molecular Bioengineering of Bacterial Magnetic Particles for Biotechnological Applications. Magnetoreception and Magnetosomes in Bacteria, Springer.","DOI":"10.1007\/11741862"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Varadan, V.K., Chen, L., and Xie, J. (2008). Nanomedicine: Design and Applications of Magnetic Nanomaterials, Nanosensors and Nanosystems, John Wiley & Sons.","DOI":"10.1002\/9780470715611"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Jacinto, M.J., Trabuco, J.R.C., Vu, B.V., Garvey, G., Khodadady, M., Azevedo, A.M., Aires-Barros, M.R., Chang, L., Kourentzi, K., and Litvinov, D. (2018). Enhancement of lateral flow assay performance by electromagnetic relocation of reporter particles. PLoS ONE, 13.","DOI":"10.1371\/journal.pone.0186782"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Nikitin, M.P., Orlov, A.V., Sokolov, I.L., Minakov, A.A., Nikitin, P.I., Ding, J., Bader, S.D., Rozhkova, E.A., and Novosad, V. (2018). Ultrasensitive Detection Enabled by Nonlinear Magnetization of Nanomagnetic Labels. arXiv.","DOI":"10.1039\/C8NR01511B"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"260","DOI":"10.1016\/j.jmmm.2017.10.078","article-title":"Multiplex biosensing with a highly sensitive magnetic nanoparticle quantification method","volume":"459","author":"Nikitin","year":"2018","journal-title":"J. Magn. Magn. Mater."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"423","DOI":"10.1016\/j.bios.2015.12.049","article-title":"Rapid dry-reagent immunomagnetic biosensing platform based on volumetric detection of nanoparticles on 3D structures","volume":"79","author":"Orlov","year":"2016","journal-title":"Biosens. Bioelectron."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"195","DOI":"10.1016\/j.bios.2011.08.019","article-title":"Detection of rolling circle amplified DNA molecules using probe-tagged magnetic nanobeads in a portable AC susceptometer","volume":"29","author":"Mezgerb","year":"2011","journal-title":"Biosens. Bioelectron."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Makiranta, J., Verho, J., Lekkala, J., and Matintupa, N. (September, January 30). Novel Measurement Method for Magnetic Particles. Proceedings of the 2006 International Conference of the IEEE Engineering in Medicine and Biology Society, New York, NY, USA.","DOI":"10.1109\/IEMBS.2006.259441"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"372","DOI":"10.1109\/JSEN.2004.839892","article-title":"Integrated inductive sensors for the detection of magnetic microparticles","volume":"5","author":"Baglio","year":"2005","journal-title":"IEEE Sens. J."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"120","DOI":"10.1109\/TNANO.2007.909068","article-title":"Faraday\u2019s Induction Experiment in Nano-Transformers","volume":"7","author":"Kim","year":"2008","journal-title":"IEEE Trans. Nanotechnol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"465501","DOI":"10.1088\/0957-4484\/21\/46\/465501","article-title":"Magnetic bead detection using nano-transformers","volume":"21","author":"Kim","year":"2010","journal-title":"Nanotechnology"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"111","DOI":"10.1042\/EBC20150012","article-title":"Lateral flow assays","volume":"60","author":"Koczula","year":"2016","journal-title":"Essays Biochem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"47","DOI":"10.1016\/j.bios.2015.05.050","article-title":"Nanoparticle-based lateral flow biosensors","volume":"73","year":"2015","journal-title":"Biosens. Bioelectron."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Gilmore, J., Islam, M., and Martinez-Duarte, R. (2016). Challenges in the Use of Compact Disc-Based Centrifugal Microfluidics for Healthcare Diagnostics at the Extreme Point of Care. Micromachines, 7.","DOI":"10.3390\/mi7040052"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"438","DOI":"10.1016\/j.biotechadv.2013.01.006","article-title":"Point-of-care assays for tuberculosis: Role of nanotechnology\/microfluidics","volume":"31","author":"Wang","year":"2013","journal-title":"Biotechnol. Adv."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1016\/j.chempr.2017.01.009","article-title":"Small but Perfectly Formed? Successes, Challenges, and Opportunities for Microfluidics in the Chemical and Biological Sciences","volume":"2","author":"Chiu","year":"2017","journal-title":"Chem"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"2210","DOI":"10.1039\/c3lc50169h","article-title":"Paper-based microfluidic point-of-care diagnostic devices","volume":"13","author":"Yetisen","year":"2013","journal-title":"Lab Chip"},{"key":"ref_27","unstructured":"James, H.R. (2017, June 07). OSH Park\u2014An Electric Ecosystem. Available online: https:\/\/oshpark.com\/."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"841","DOI":"10.1119\/1.19136","article-title":"Classical Electrodynamics, 3rd ed","volume":"67","author":"Jackson","year":"1999","journal-title":"Am. J. Phys."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"763","DOI":"10.1016\/0011-2275(91)90241-N","article-title":"Calibration constant calculations for magnetic susceptibility measurements","volume":"31","author":"Khoder","year":"1991","journal-title":"Cryogenics"},{"key":"ref_30","first-page":"1","article-title":"Experimental Researches in Electricity. Fifteenth Series","volume":"129","author":"Faraday","year":"1839","journal-title":"Philos. Trans. R. Soc. Lond."},{"key":"ref_31","unstructured":"Chahal, A. (2019, October 03). AMPERES|INTEGRATED Engineering Software. Available online: https:\/\/www.integratedsoft.com\/Products\/amperes.aspx."},{"key":"ref_32","unstructured":"(2019, July 22). Standard Adembeads. Available online: https:\/\/www.ademtech.com\/magnetic-particles\/in-vitro-diagnostic\/standard-adembeads."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/24\/5433\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T13:40:54Z","timestamp":1760190054000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/24\/5433"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,12,10]]},"references-count":32,"journal-issue":{"issue":"24","published-online":{"date-parts":[[2019,12]]}},"alternative-id":["s19245433"],"URL":"https:\/\/doi.org\/10.3390\/s19245433","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,12,10]]}}}