Ultrasensitive Detection Enabled by Nonlinear Magnetization of Nanomagnetic Labels

TL;DR

This paper demonstrates ultrasensitive detection of nanomagnetic labels using their nonlinear magnetization response, achieved through irreversible magnetic state transitions in ferromagnetic disks, enabling real-time biodistribution tracking in live animals.

Contribution

The study introduces a novel detection method leveraging nonlinear magnetic responses of patterned ferromagnetic disks, significantly enhancing sensitivity for biological and medical applications.

Findings

Record sensitivity of ~3.5x10^-9 emu achieved at room temperature.

Successful detection and quantification of unbound disks in live animals.

Nonlinear magnetic response enables ultrasensitive detection in complex biological environments.

Abstract

Geometrically confined magnetic particles due to their unique response to external magnetic fields find a variety of applications, including magnetic guidance, heat and drug delivery, magneto-mechanical actuation, and contrast enhancement. Highly sensitive detection and imaging techniques based on nonlinear properties of nanomagnets were recently proposed as innovative strong-translational potential methods applicable in complex, often opaque, biological systems. Here we report on significant enhancement of the detection capability using optical-lithography-defined, ferromagnetic iron-nickel alloy disk-shaped particles. We show that an irreversible transition between a strongly non-collinear (vortex) and single domain states, driven by an alternating magnetic field translates into a nonlinear magnetic response that enables ultrasensitive detection of these particles. The record sensitivity of ~ 3.5x10-9 emu, which is equivalent to ~39 pg of magnetic material is demonstrated at room temperature for arrays of patterned disks. We also show that unbound disks re-suspended in aqueous buffer can be successfully detected and quantified in real-time when administrated into a live animal allowing for tracing their biodistribution. Use of nanoscale ferromagnetic particles with engineered nonlinear properties opens prospects for further enhancing sensitivity, scalability and tunability of noise-free magnetic tag detection in high-background environments for various applications spanning from biosensing and medical imaging to anti-counterfeiting technologies.