Second-Harmonic Magnetoacoustic Ultrasound from Magnetic Nanoparticles under Radiofrequency Electromagnetic Fields

TL;DR

This study demonstrates that magnetic nanoparticles generate second-harmonic ultrasound signals under radiofrequency electromagnetic fields, suggesting a potential mechanism for cell damage and new avenues for magnetoacoustic theragnostics.

Contribution

The paper provides experimental evidence of second-harmonic ultrasound generation by magnetic nanoparticles under RF EMFs, highlighting a novel magnetoacoustic interaction mechanism.

Findings

Second-harmonic ultrasound signals observed only in samples with MNPs.

Aligned MNP clusters significantly increase SH signal amplitude.

US generation may cause cell damage without temperature increase.

Abstract

We report experimental evidence of mechanical wave generation by magnetic nanoparticles (MNPs) under radiofrequency electromagnetic fields (EMFs, 65mT, 800 kHz, at 100ms bursts) in the ultrasonic (US) frequency range. We developed an experimental setup to detect the second harmonic (SH) signal under isothermal conditions. This SH-US signal was observed only in samples containing MNPs and consequently originated from the EMF interaction on samples containing MNPs. These findings suggest that US generation due to magneto-acoustic interaction in the MNPs could be responsible for the cell damage induced by EMF in cells containing MNPs without increasing the temperature. Experiments performed on magnetically aligned MNP clusters in gelatin significantly enhance the amplitude of the SH signal compared to non-aligned samples. This phenomenon could pave the way for new theoretical and practical approaches as for 'in vivo' magnetoacoustics theragnostic.