Precise detection of trace magnetic nanoparticles based on spin-exchange-relaxation-free magnetometers

The precise quantitative analysis of magnetic nanoparticles is crucial for their applications in biomedicine. This work presents the research and development of a measurement system based on a compact spin–exchange–relaxation–free atomic magnetometer, capable of rapidly detecting the concentration and flow rate of magnetic nanoparticles in solution. By designing spatial magnetic field gradients, the system creates a quasi-zero field environment for the magnetometer while providing a large excitation magnetic field for the magnetic nanoparticles. The droplet method facilitates the preparation of minimal amounts of nanoparticle samples. With a sensitivity of 25 fT/Hz, the magnetometer system can measure concentrations as low as 0.1 mg/ml in a 2 μl sample, corresponding to a nanoparticle mass of 200 ng, with a measurement error of less than 11.8 ng. This method's strengths lie in its minimal sample consumption and single-measurement low mistake, rendering it highly suitable for rapid detection or applications involving small-volume samples, particularly in immunoassay reagents. In addition to measuring particle concentration, this system can also monitor the flow rate of nanoparticles during the measurement process, providing a noninvasive means for dynamic monitoring.