Shim-on-Chip Design for Microfluidic NMR Detectors

Area of Science:

• Magnetic Resonance Imaging
• Microfluidics
• Spectroscopy

Background:

• Shimming small sample volumes in microfluidic Nuclear Magnetic Resonance (NMR) probes using conventional shim coils presents significant challenges due to limited sample size.
• Conventional shimming methods struggle with precise positioning of microliter samples within the inhomogeneous magnetic field of the NMR magnet.

Purpose of the Study:

• To introduce a novel Shim-on-Chip system for efficient shimming of capillary samples in microfluidic NMR applications.
• To demonstrate the effectiveness of this system as a simple, cost-efficient, and easily constructible alternative to traditional shim coils.

Main Methods:

• A Shim-on-Chip system was designed using a series of parallel wires placed perpendicular to the main magnetic field (B0).
• These wires, integrated into a flat ribbon cable positioned over the NMR detector (stripline), allowed for independent current control via a 16-channel digital-to-analog converter (DAC).
• The system was tested on a 144 MHz NMR spectrometer and a 400 MHz Rapid-Melt Dynamic Nuclear Polarization (DNP) system.

Main Results:

• The Shim-on-Chip system achieved narrow spectral line widths of 2.2 Hz (50% intensity) and 27 Hz (0.55% intensity) on a 144 MHz NMR spectrometer without auxiliary room temperature shims.
• The system demonstrated flexibility in generating magnetic fields to counteract one-dimensional magnetic field inhomogeneity, particularly suited for the elongated geometry of capillary samples.
• Effective shimming was also demonstrated in a 400 MHz DNP system, even with an off-center sample.

Conclusions:

• The Shim-on-Chip system offers a practical and intuitive solution for shimming microfluidic NMR samples, simplifying the process compared to conventional methods.
• Its integrated nature within the NMR probe ensures consistent sample centering, leading to improved spectral quality and easier manual adjustment.
• This technology presents a valuable advancement for microfluidic NMR spectroscopy and DNP applications, enhancing spectral resolution and simplifying experimental procedures.