Bead magnetorelaxometry with an on-chip magnetoresistive sensor

Area of Science:

• Physics
• Materials Science
• Biotechnology

Background:

• Magnetorelaxometry (MRX) is a technique used to characterize magnetic nanoparticles.
• Conventional MRX often requires complex setups for generating magnetic fields and detecting signals.
• Microfluidic systems offer precise control over sample manipulation and integration with sensors.

Purpose of the Study:

• To demonstrate magnetorelaxometry measurements using a microfluidic system integrated with a planar Hall effect sensor.
• To investigate the feasibility of using the sensor's bias current as an alternating magnetic field source.
• To analyze the complex magnetic susceptibility spectra of magnetic bead suspensions.

Main Methods:

• Utilized a microfluidic system with an embedded planar Hall effect sensor chip.
• Employed the sensor's bias current to generate an alternating magnetic field for magnetizing magnetic beads.
• Recorded the complex magnetic susceptibility spectra as the 2nd harmonic of the sensor's response.
• Injected magnetic bead suspensions into the microfluidic system for measurements.

Main Results:

• Successfully detected complex magnetic susceptibility signals from magnetic bead suspensions.
• Observed that the signal intensity scales with the concentration of magnetic beads.
• The recorded spectra followed the Cole-Cole expression, characteristic of Brownian relaxation.
• Noted an offset in Brownian relaxation frequency compared to conventional MRX.
• Identified signal time dependence consistent with sedimented beads.

Conclusions:

• The integrated microfluidic and planar Hall effect sensor system is effective for magnetorelaxometry.
• This approach allows for the characterization of magnetic bead suspensions based on their magnetic properties.
• The findings suggest potential for developing compact and sensitive MRX devices for various applications.