Understanding the opposite optomagnetic responses of different-sized magnetic nanoparticles

Magnetic nanoparticle agglutination-based optomagnetic biosensing can rapidly detect various biomolecules, such as viral proteins, nucleic acids, and cancer biomarkers, making it promising for point-of-care testing in hospitals and other health care facilities. In this technique, target biomolecules bind to magnetic nanoparticles, causing them to aggregate. Manipulating these aggregates creates a measurable optomagnetic signal.

However, studies have shown that the optomagnetic signal of magnetic nanoparticle dimers is opposite to that of magnetic nanoparticle monomers, a phenomenon that has not been explained. Yang et al. developed and experimentally verified a numerical model to investigate the distinct responses of monomers and dimers.

By calculating the optomagnetic signal in a magnetic nanoparticle agglutination assay, the authors showed that Mie scattering of the dimers leads to its inverse optomagnetic response compared to the monomers. Previous work had suspected, but not confirmed, the culprit of this phenomenon was Mie scattering, an effect seen when particles have diameters nearing the wavelength of the incident light.

“This numerical model offers a means to investigate the intricate relationships between various physical properties, including optical, magnetic, and thermodynamic properties, as well as their effects on the optomagnetic sensing performance,” said author Jing Zhong.

Based on this model, the authors proposed an optomagnetic signal analysis method that is more accurate within a wider detection range than the conventional method. A better understanding of Mie scattering in magnetic nanoparticle agglutination-based optomagnetic biosensing will help researchers analyze the optomagnetic spectrum and advance this technology.

“The model could be used to develop novel optomagnetic sensors that allow more sensitive and precise analyses of on-particle biorecognitions,” said author Bo Tian.

Source: “Mie scattering in magnetic nanoparticle agglutination-based optomagnetic biosensing,” by Yulin Yang, Jiajun Cui, Xinchao Cui, Wenzhong Liu, Bo Tian, and Jing Zhong, Applied Physics Letters (2024). The article can be accessed at https://doi.org/10.1063/5.0241272 .