Microfluidic-Integrated Chip Resonators for Electron Spin Sensing in Submicromolar, Submicroliter Solutions.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Microfluidics
• Materials Science

Background:

• Planar microresonators reduce sample volumes for magnetic resonance spectroscopies to the nanoliter scale.
• Interrogating nanoliter samples on planar sensors is challenging due to the lack of microfluidic devices offering small volume and long-term stability.

Purpose of the Study:

• To develop microfluidic devices for submicroliter sample volumes with long-term physical stability and storability.
• To integrate these microfluidics with planar sensors for enhanced electron paramagnetic resonance (EPR) spectroscopy.
• To demonstrate a 3D-printed microfluidic with self-contained actuation for sample retraction and storage.

Main Methods:

• Fabrication of microfluidic devices using laser cutting or 3D printing.
• Integration with planar inverse anapole (PIA) microresonators.
• Acquisition of continuous wave (CW) electron paramagnetic resonance (EPR) spectra of nitroxide radicals.

Main Results:

• Demonstrated microfluidic devices with submicroliter total volume and long-term sample stability.
• Achieved a concentration sensitivity of 330 ± 40 nmol L⁻¹ and a limit of 800 ± 100 nmol L⁻¹/mT√Hz.
• Confirmed an active sample volume of no greater than 30 nL.

Conclusions:

• Developed innovative microfluidic devices for stable, dead-volume-free placement of nanoliter-scale solutions on planar sensors.
• Significantly advanced the sensitivity of EPR spectroscopy through microfluidic integration.
• Enabled long-term storage and handling of small-volume samples for magnetic resonance applications.