Planar-coil-based Micro-detection in Nuclear Magnetic Resonance Spectroscopy

This paper reports the design, fabrication and preliminary tests of lab-built probes for microliter-level NMR spectroscopy (Nuclear Magnetic Resonance). The detection is based on the planar microcoils fabricated on glass substrate by MEMS (Micro Electronic Mechanical System) technology with SU-8 photoresist. The measured Q values are about 20 at 63.89 MHz for the microcoils, i.d. $1000 \mu $m, wire width $80 \mu $m, 7 turns. The characterization of the lab-built microcoil-based probes has been performed in NMR experiments for 4 g/L CuSO4 samples of $200 \mu $L. Using the square microcoil fabricated, with the cone-type container the SNR (Signal-to-Noise Ratio) and the Linewidth at 1.5 Tesla is 101.7 and 450.1 Hz, respectively. And with the tube-type container the SNR and the Linewidth is 17 and 229.6 Hz, respectively. It was shown that the resolution degraded about one-hundred percent due to container-introduced distortion on B0 container. On the other hand a good couple of container shape with the profile of B1 will improve the sensitivity. And the resolution could be improved by optimization on the structure of the probe. Towards nano-liter NMR spectroscopy, the sample volume under detection could be reduced further. Honestly to say, the planar microcoil NMR has unsealed the integration with chip-based microfluidics in the emerging world of micro-Total Analysis Systems ($\mu $ TAS).