A tabletop Optically Pumped Magnetometer setup for the monitoring of magnetic nanoparticle clustering and immobilization using Thermal Noise Magnetometry

TL;DR

This paper introduces a tabletop optically pumped magnetometer setup for Thermal Noise Magnetometry, providing a flexible, accessible alternative to SQUID sensors for monitoring magnetic nanoparticle clustering and immobilization in various biological and chemical processes.

Contribution

The study demonstrates the feasibility of using OPMs in a tabletop setup for TNM, matching SQUID performance and enabling new applications in biological and chemical nanoparticle analysis.

Findings

OPM setup agrees with SQUID measurements for nanoparticle samples.

The setup effectively monitors nanoparticle aggregation and immobilization.

It is suitable for biological processes with slow magnetization dynamics.

Abstract

Many characterization techniques for magnetic nanoparticles depend on the usage of external fields. This is not the case in Thermal Noise Magnetometry (TNM), where thermal fluctuations in the magnetic signal of magnetic nanoparticle ensembles are measured without any external excitation. This can provide valuable information about the fundamental dynamical properties of the particles, due to the purely observative experiments of this relatively new technique. Until now, TNM signals have been detected only by a superconducting quantum interference device (SQUID) sensor. We present a tabletop setup using Optically Pumped Magnetometers (OPMs) in a small magnetic shield, offering a flexible and accessible alternative and show the agreement between both measurement systems for two different commercially available nanoparticle samples. We argue that the OPM setup with high accessibility complements the SQUID setup with high sensitivity and bandwidth. Furthermore, because of its excellent sensitivity in the lower frequencies, the OPM tabletop setup is well suited to monitor aggregation processes where the magnetization dynamics of the particles tend to slow down, e.g. in biological processes. As a proof of concept, we show for three different immobilization and clustering processes the changes in the noise spectrum measured in the tabletop setup: 1) the aggregation of particles due to the addition of ethanol, 2) the formation of polymer structures in the sample due to UV exposure, and 3) the cellular uptake of the particles by THP-1 cells. From our results we conclude that the tabletop setup offers a flexible and widely adoptable sensor measurement unit to monitor the immobilization and clustering of magnetic nanoparticles over time for different applications.