Abstract
Magnetorelaxometry (MRX) is a promising new biosensing technique for point-of-care diagnostics. Historically, magnetic sensors have been primarily used to monitor the stray field of magnetic nanoparticles bound to analytes of interest for immunoassays and flow cytometers. In MRX, the magnetic nanoparticles (MNPs) are first magnetized and then the temporal response is monitored after removing the magnetic field. This new sensing modality is insensitive to the magnetic field homogeneity making it more amenable to low-power portable applications. In this work, we systematically investigated time-domain MRX by measuring the signal dependence on the applied field, magnetization time, and magnetic core size. The extracted characteristic times varied for different magnetic MNPs, exhibiting unique magnetic signatures. We also measured the signal contribution based on the MNP location and correlated the coverage with measured signal amplitude. Lastly, we demonstrated, for the first time, a GMR-based time-domain MRX bioassay. This approach validates the feasibility of immunoassays using GMR-based MRX and provides an alternative platform for point-of-care diagnostics.
Highlights
For the past two decades, magnetic biosensors have received considerable attention as they offer several key advantages over conventional and competing sensing methods[4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
The reference sensors were coated with Bovine serum albumin (BSA) while active sensors were functionalized with biotin, which facilitated binding with the magnetic nanoparticles (MNPs) through the high affinity streptavidin-biotin interaction
The results showed that other contributors need to be considered as well
Summary
For the past two decades, magnetic biosensors have received considerable attention as they offer several key advantages over conventional and competing sensing methods[4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. In addition to the inherent advantages of magnetic biosensing, MR biosensors can be operated at room temperature, have high low-field sensitivity, and have comparably high transduction efficiency These MR-based sensors operate on a quantum mechanical effect (either spin-dependent scattering or tunneling) where the resistance is proportional to the magnetic field with magnetoresistance ratios ranging from 5% to >200% for modern devices[8,28]. These MR biosensors utilized static magnetometry where one detects the MNP’s stray field in response to a DC or fixed frequency AC magnetic field. We use these findings to optimize the system and perform a proof-of-principle magnetic immunoassay, which is, to the best of our knowledge, the first time that GMR sensors have been reported for an MRX bioassay
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