Magnetic Susceptibility-Based Detection of Fusobacterium Nucleatum in Human Saliva

This letter presents an innovative method for rapid and precise measurement of bacteria in liquid samples for point-of-care testing. The method utilizes the bacteria concentration-dependent ac susceptibility of magnetic nanoparticles, allowing for efficient and practical bacterial detection. The ac susceptibility of the magnetic nanoparticles/bacteria aggregate exhibits a decrease proportional to the bacteria concentration, attributed to the influence of bacteria on the magnetic coupling between the magnetic nanoparticles and magnetic dynamic response of the aggregate. To validate the performance of our method, we conducted measurements on Fusobacterium nucleatum samples obtained from both healthy individuals and cancer patients. The results demonstrated a robust correlation (correlation factor up to 0.94) between our measurements and the results obtained through quantitative polymerase chain reaction (qPCR) analysis, highlighting the high precision and accuracy of our method in quantifying bacteria, which is comparable to a qPCR system. The simplified apparatus not only reduces costs but also saves time by eliminating the need for DNA amplification of short segments, making it a promising alternative for rapid and precise bacterial measurement in point-of-care testing.

I. Introduction

Magnetic nanoparticles (MNPs) have attracted significant interest in biology and medicine due to their diverse applications, including biosensing, targeted drug delivery, magnetic resonance imaging, and magnetic hyperthermia [Laurent 2008, Etemadi 2020, Shikano 2022, Tonthat 2023a, 2023b, 2023c]. Magnetic immunoassays using MNPs have emerged as a promising diagnostic tool for point-of-care testing. This innovative approach utilizes MNPs coated with specific detecting antibodies that selectively capture biological targets, such as viruses, bacteria, and proteins, through antigen–antibody reactions [Wu 2019, Cao 2020, Yari 2023. To maximize the potential of MNPs in bioassays, understanding and tailoring their magnetic behavior is crucial. Major magnetic property characterization methods, such as magnetization and susceptibility measurements [Wu 2019, Zhong 2012, 2014a, 2014b], play pivotal roles in gaining insights into the magnetic properties of MNPs, thereby enhancing bioassay performance. Recent advancements, including magnetic relaxation and ac susceptibility-based measurement methods, have further enabled the sensitive detection of various biological targets [Kötitz 1999, Astalan 2004, Chung 2005, Krishna 2016, Mizoguchi 2016, Enpuku 2017, Hirota 2023].