Magnetoacoustic Sensing of Magnetic Nanoparticles

Stephan Kellnberger, Amir Rosenthal, Ahne Myklatun, Gil G. Westmeyer, George Sergiadis, and Vasilis Ntziachristos

Phys. Rev. Lett. 116, 108103 – Published 10 March 2016

Abstract

The interaction of magnetic nanoparticles and electromagnetic fields can be determined through electrical signal induction in coils due to magnetization. However, the direct measurement of instant electromagnetic energy absorption by magnetic nanoparticles, as it relates to particle characterization or magnetic hyperthermia studies, has not been possible so far. We introduce the theory of magnetoacoustics, predicting the existence of second harmonic pressure waves from magnetic nanoparticles due to energy absorption from continuously modulated alternating magnetic fields. We then describe the first magnetoacoustic system reported, based on a fiber-interferometer pressure detector, necessary for avoiding electric interference. The magnetoacoustic system confirmed the existence of previously unobserved second harmonic magnetoacoustic responses from solids, magnetic nanoparticles, and nanoparticle-loaded cells, exposed to continuous wave magnetic fields at different frequencies. We discuss how magnetoacoustic signals can be employed as a nanoparticle or magnetic field sensor for biomedical and environmental applications.

Received 22 September 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.108103

Physics Subject Headings (PhySH)

Magnetic interactions Medical physics & public health

Nanoparticles Tumors

Magnetic techniques

Polymers & Soft MatterPhysics of Living Systems

Authors & Affiliations

Stephan Kellnberger^1,2,3,*, Amir Rosenthal^2,3,4, Ahne Myklatun^3,5, Gil G. Westmeyer^3,5,6, George Sergiadis⁷, and Vasilis Ntziachristos^2,3,†

¹Cardiovascular Research Center, Cardiology Division, Massachusetts General Hospital, Harvard Medical School, 185 Cambridge Street, Boston, Massachusetts 02114, USA
²Chair for Biological Imaging, Technische Universität München, Trogerstraße 9, 81675 München, Germany
³Institute for Biological and Medical Imaging, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 München, Germany
⁴Andrew and Erna Viterbi Faculty of Electrical Engineering, The Technion—Israel Institute of Technology, Haifa 32000, Israel
⁵Institute of Developmental Genetics (IDG), Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 München, Germany
⁶Department of Nuclear Medicine, Technische Universität München, Ismaninger Str. 22, 81675 München, Germany
⁷Department of Electrical and Computer Engineering, Aristotle University, Egnatia Str., 54124 Thessaloniki, Greece

^*Corresponding author. stephan.kellnberger@tum.de
^†Corresponding author. v.ntziachristos@tum.de

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Issue

Vol. 116, Iss. 10 — 11 March 2016

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Images

Figure 1
Concept of magnetoacoustic signal induction. (a) Components of the magnetoacoustic setup. Power supply (PS), modulator (M), water chiller (W), driver (D). (b) Magnetoacoustic sensing using a PZT transducer. The sample comprises a steel rod located within the coil. (c) rf-free magnetoacoustic sensing employing a fiber-Bragg-based interferometric ultrasound sensor in a horizontally arranged solenoid (water tank not displayed). The optical sensor comprises optical filters (F), an erbium-doped fiber amplifier (EFDA), a $99 / 1$ optical splitter (S), a demodulator (Demod), and the $π$ -shifted FBG sensing unit. (d) Magnetoacoustic sensing of a steel rod specimen using PZT based ultrasound detection. rf interference due to the nonlinearity of the rf amplifier (blue dotted line) and experimental confirmation of the second harmonic magnetoacoustic signal (red line) induced in conducting material at $f_{MA} = 2 f_{rf}$ . Inset shows the quadratic increase of detected magnetoacoustic signal (red crosses) as a function of the linearly rising $B$ field compared to the expected theory (dashed black curve) and a linear relationship (dotted green line).
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Figure 2
Magnetic fluid heating and magnetoacoustic signal induction. (a) Schematic of temperature sensing using different nanoparticles. (b) Heating rates of 6 different magnetic fluids after 10 min. magnetic field exposure. The magnetic field-normalized temperature increase is shown at 5 discrete frequency steps. (c) Magnetoacoustic sensing of magnetic nanoparticles using the interferometric ultrasound sensor. The red curve displays a magnetoacoustic signal from sample S1 at $f_{MA} = 2.3208 MHz$ excited at $f_{rf} = 1.1604 MHz$ . The blue dotted curve depicts the baseline measurement without coupling medium, confirming rf-interference free detection. (d) Magnetoacoustic sensing at $f_{rf} = 508.3 kHz$ using sample S2. The red curve shows the magnetoacoustic response at $f_{MA} = 2 f_{rf} = 1.0166 MHz$ while the blue curve represents the rf-free baseline measurement when the interferometer is turned off.
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Figure 3
Magnetoacoustic sensing of macrophages with nanoparticles. (a) Heating rates of ANA-1 cells loaded with magnetic particles C1-a (cyan diamond line), C1-b (purple triangle line), and C2-a (red dotted line) after subtraction of background heating. (b) Second harmonic acoustic response of ANA-1 cells incubated with fluidMAG-Amine (red dotted line). The control measurement of unlabeled ANA-1 cells (blue diamond line) and the noise measurement after disabling the optical sensor (green triangle line) show the nonlinear EMI response of the rf amplifier.
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