Dynamic Magnetic Excitation Detection Method for Low-Concentration Superparamagnetic Particles via Quartz Crystal Microbalance

Magnetic biomarker detection and monitoring at low concentrations are critical for the early diagnosis of many diseases and for accurately identifying specific biomolecules. Previously reported highly sensitive detection methods rely on magnetic sensors to detect the stray fields of magnetic labels (usually magnetic beads). The random noise generated by the Brownian motion of magnetic beads in solution makes it difficult to reduce further the limit of detection (LOD) of this measurement. Therefore, we propose a low-concentration magnetic beads sensor and a dynamic magnetic excitation detection method. The intensity of magnetization motion under the ac excitation magnetic field detected by the quartz crystal microbalance (QCM) realizes the measurement of the magnetic bead concentration in the solution. The experimental results show that the LOD of the proposed sensor in $2.8~\mu \text{m}$ magnetic bead solution is 10 ng/mL and displays an approximate linear detection characteristic in the range of 20–100 ng/mL. The intensity of magnetization detected by QCM has an approximately linear relationship with the magnetic bead concentration. Given the wide application of magnetic-labeled biomolecule detection and its huge application prospects in early disease detection and precision medicine, this method provides an inexpensive, fast, and flexible detection technology for the general labeling analysis of magnetic labels in biomolecule detection.