Breast cancer represents a significant global health concern among women. The intricate processes and pathways underlying metastasis contribute to the challenging prognoses experienced by some patients. Extracellular vesicles (EVs) are membrane-bound structures characterized by phospholipid bilayers, capable of secretion by a multitude of cell types. The contents of these vesicles encompass a diverse assortment of lipids, proteins, nucleic acids, and cellular metabolites. The tumor microenvironment (TME) comprises a complex network involving tumor cells, non-cancerous cells, and an array of molecules they generate and release. Components include the extracellular matrix, cancer-associated fibroblasts, inflammatory immune cells, tumor-associated vasculature, and EVs discharged by these cellular entities. Within the TME, EVs serve as a mechanism akin to the "Trojan Horse," exerting significant influence in tumor initiation, progression, metastasis, and responses to therapeutic interventions. EVs originating from tumor cells and associated entities within the TME bolster processes such as stimulating angiogenesis adjacent to tumor sites, establishing pre-metastatic niches in distant anatomical regions, and inducing transformative changes in cancer cells to acquire characteristics promoting invasion, angiogenesis, immune evasion, distant metastasis, and resistance to chemotherapy. Noteworthy is the unique capacity of EVs to traverse biological barriers due to their inherent biocompatibility, rendering them promising candidates for innovative drug delivery systems. This attribute presents an avenue to surmount the constraints of traditional cancer treatments. This scholarly inquiry delves into the pathogenic mechanisms of EVs in breast cancer and delves into prospective therapeutic interventions, offering a groundwork for forthcoming precision-guided therapies tailored to breast cancer.

We developed a highly sensitive measurement system of ac magnetic fields for magnetic nanoparticle imaging (MPI). First, we developed a detection system using pickup coils made of cooled Cu Litz-wire and high-critical-temperature superconductor (HTS) tape. The pickup coils were connected to a resonant capacitor in order to enhance the signal voltage generated in the pickup coils. The magnetic field noise at the resonant frequency of about 9 kHz was as low as 13 fT/Hz ^1/2 and 12 fT/Hz ^1/2 for the Cu and HTS coils, respectively. Next, we demonstrated the detection of nanoparticles using the cooled Cu coil and the third harmonic signal generated by the nonlinear magnetization of nanoparticles. An excitation field having a frequency of 3 kHz and root mean square value of 1.6 mT was applied to the magnetic particles, and the third harmonic signal at 9 kHz was detected that reduced the interference from the excitation field. We demonstrated the detection of 100 μg of magnetic nanoparticles. We obtained a clear contour map of the magnetic field from the particles, and could detect the particles located as far as 100 mm under the pickup coil.

The core size distribution is an important physical characteristic of magnetic nanoparticles (MNPs) because it seriously affects biomedical and biological applications. In this study, we proposed an improved method for estimating the distributions, which optimizes the excitation frequency based on AC susceptibility to avoid the effects of Brownian relaxation. Moreover, the first, third, and fifth magnetization harmonics under different excitation field strengths are used for estimating core size distributions to avoid measuring higher harmonics. The experiment results show that the improved AC harmonic method can accurately and quickly estimate the distribution of large core sizes compared with the method of static magnetization (M–H) curves, which is a competitive advantage in MNP immunoassays.

We developed a narrowband magnetic particle imaging (MPI) system that uses third-harmonic signal detection and electrical scanning of the field free point (FFP). Comparing with mechanical scanning, we can decrease the measurement time significantly and increase the signal-to-noise ratio as well. For electrical scanning, we designed and constructed gradient and shift coils. The gradient coil consisting of four pieces of planar coils generated the gradient field with a field gradient of 0.4 T/m at a height of 25 mm from the coil surface. The FFP can be moved ±8 mm by supplying a current of ±6.6 A to the shift coil. Using the developed system, we detected two magnetic nanoparticle (MNP) samples located at a depth of 35 mm below the pickup coil with a spacing of 10 mm. By applying an excitation field of 1 mT at 22.75 kHz, we measured the third-harmonic signal from the MNP samples and obtained a contour map of the signal field in an area of 16 × 16 mm ² . Then, we converted the field map into an MNP distribution using singular value decomposition method. It was shown that the spatial resolution of the reconstructed MNP distribution was improved compared with that of the measured contour map of the signal field. The spatial resolution for MNP detection in MNP distribution was 5 mm and two MNP samples were distinguished clearly. This result indicated that MPI using electrical scanning of the FFP was successfully performed.