A benchtop induction-based AC magnetometer for a fast characterization of magnetic nanoparticles

Abstract

In this study, we report a development of a benchtop induction-based AC magnetometer to realize a simple, wideband, and sensitive AC magnetometer for bio-sensing applications and characterization of magnetic nanoparticles (MNPs). We investigate the inductance and parasitic capacitance of six different pickup coil geometries and compare their sensitivity and usable frequency range. In the pickup coil design, the number of turns and coil section separation are varied from 200 to 400 turns, and 1 to 4 sections, respectively. We find that the usable frequency range is greatly affected by the pickup coil’s inductance due to the self-resonance phenomena compared to their parasitic capacitance. A low noise instrument amplifier circuit (AD8429, Analog Devices, USA) was integrated and fabricated on a printed circuit board to amplify the weak signal from the pickup coil. We also implement a generalized Goertzel algorithm to achieve fast signal amplitude and phase extractions at a frequency. The developed magnetometer shows a sensitivity of 10-8 Am2/√Hz at 6 Hz and a frequency range of up to 158 kHz. Using the developed AC magnetometer, we demonstrate the viscosity effect on the frequency response of thermally blocked, single-core nanoparticles (SHP30, Ocean Nanotech, USA) in glycerol solutions. The excitation frequency is swept from 5 Hz to 158 kHz at a field amplitude of 0.55 mTpp within the acquisition time of 5 minutes (51 points). As a result, the viscosity change is confirmed by the peak shifting in the imaginary magnetization curve towards lower frequency values when the wt/V% of the glycerol solution is increased. The hydrodynamic size and the average anisotropy energy ratio σ are estimated to be 60.6 nm and 25, respectively, from the complex AC magnetization. It can be expected that the developed AC magnetometer can be a valuable tool in providing a fast and reliable assessment of MNPs for bio-sensing applications.

A Review of Characterization Techniques for Ferromagnetic Nanoparticles and the Magnetic Sensing Perspective

“…Then, a variety of AC susceptometers using this technology appeared. This method can provide rapid magnetic characterization of magnetic nanoparticles [34]. The AC magnetometers can detect the magnetic responses using the Neel and Brown relaxation parameters.…”

“…To have the most accurate measurement, there is a vital need for the sensors to be very sensitive and also have a high range of excitation frequency. This will provide knowledge about all magnetic relaxations that exist in the nanoparticle system [34][35][36]. This way, it is possible to determine the magnetic properties of the nanoparticles.…”

“…This device has a constant excitation field with a value greater than 4.25 Oe and has the capability to operate between 10 kHz and 1 MHz. In [34], an induction AC magnetometer, for determining the profile of magnetic nanoparticles in bio-sensing applications, is presented. This device contains inductive coils, which offer a simple structure, economically efficient operation, as well as high frequency and dynamic range, compared to other magnetic sensors like SQUIDs, optically pumped magnetometers, or fluxgate magnetometers.…”

The Hybrid System for the Magnetic Characterization of Superparamagnetic Nanoparticles

“…The setup was able to measure magnetic losses by integrating a magnetic hysteresis loop in a range of 49 kHz to 1030 kHz. Another benchtop magnetometer was presented by Saari et al [14]. The authors wound a small excitation coil with Litz wire and tested different designs of two oppositely wound detection coils that allowed for measurements in the range from 5 Hz to 158 kHz.…”