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Open AccessArticle

Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles

1
Institute of Electrical and Biomedical Engineering, UMIT—Private University for Health Sciences, Medical Informatics and Technology, 6060 Hall in Tirol, Austria
2
Twinleaf LLC, Plainsboro Township, NJ 08536, USA
3
Department Biosignals, Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany
4
Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, 98693 Ilmenau, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Ahmed Toaha Mobashsher
Sensors 2021, 21(4), 1212; https://doi.org/10.3390/s21041212
Received: 31 December 2020 / Revised: 3 February 2021 / Accepted: 5 February 2021 / Published: 9 February 2021
(This article belongs to the Section Physical Sensors)
Magnetic nanoparticles (MNP) offer a large variety of promising applications in medicine thanks to their exciting physical properties, e.g., magnetic hyperthermia and magnetic drug targeting. For these applications, it is crucial to quantify the amount of MNP in their specific binding state. This information can be obtained by means of magnetorelaxometry (MRX), where the relaxation of previously aligned magnetic moments of MNP is measured. Current MRX with optically pumped magnetometers (OPM) is limited by OPM recovery time after the shut-off of the external magnetic field for MNP alignment, therewith preventing the detection of fast relaxing MNP. We present a setup for OPM-MRX measurements using a commercially available pulsed free-precession OPM, where the use of a high power pulsed pump laser in the sensor enables a system recovery time in the microsecond range. Besides, magnetometer raw data processing techniques for Larmor frequency analysis are proposed and compared in this paper. Due to the high bandwidth (≥100 kHz) and high dynamic range of our OPM, a software gradiometer in a compact enclosure allows for unshielded MRX measurements in a laboratory environment. When operated in the MRX mode with non-optimal pumping performance, the OPM shows an unshielded gradiometric noise floor of about 600 fT/cm/Hz for a 2.3 cm baseline. The noise floor is flat up to 1 kHz and increases then linearly with the frequency. We demonstrate that quantitative unshielded MRX measurements of fast relaxing, water suspended MNP is possible with the novel OPM-MRX concept, confirmed by the accurately derived iron amount ratios of MNP samples. The detection limit of the current setup is about 1.37 μg of iron for a liquid BNF-MNP-sample (Bionized NanoFerrite) with a volume of 100 μL. View Full-Text
Keywords: optically pumped magnetometer; free-precession decay; pulsed magnetometer; magnetic nanoparticles; magnetorelaxometry; unshielded; low dead time; high bandwidth; portable setup optically pumped magnetometer; free-precession decay; pulsed magnetometer; magnetic nanoparticles; magnetorelaxometry; unshielded; low dead time; high bandwidth; portable setup
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MDPI and ACS Style

Jaufenthaler, A.; Kornack, T.; Lebedev, V.; Limes, M.E.; Körber, R.; Liebl, M.; Baumgarten, D. Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles. Sensors 2021, 21, 1212. https://doi.org/10.3390/s21041212

AMA Style

Jaufenthaler A, Kornack T, Lebedev V, Limes ME, Körber R, Liebl M, Baumgarten D. Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles. Sensors. 2021; 21(4):1212. https://doi.org/10.3390/s21041212

Chicago/Turabian Style

Jaufenthaler, Aaron; Kornack, Thomas; Lebedev, Victor; Limes, Mark E.; Körber, Rainer; Liebl, Maik; Baumgarten, Daniel. 2021. "Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles" Sensors 21, no. 4: 1212. https://doi.org/10.3390/s21041212

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