NANOLITER VOLUME, HIGH-RESOLUTION NMR MICROSPECTROSCOPY USING A 60-MU-M PLANAR MICROCOIL

Previous studies demonstrated the feasibility of using 100-mu m inner diameter planar spiral inductors (microcoils) as detectors in H-1 nucl ear magnetic resonance (NMR) microspectroscopy. However, high-resoluti on NMR applications were not possible due to poor spectral resolution and low signal-to-noise ratio (SNR). These limitations in performance have now been largely overcome by using a nonconductive liquid fluoroc arbon (FC-43) to minimize the effects of susceptibility mismatch betwe en materials, and by carefully optimizing the microcoil geometry for m aximum SNR. In this study, liquid samples were loaded into a fused sil ica capillary (75-mu m inner diameter, 147-mu m outer diameter). The c apillary was positioned 50 mu m above a 3.5-turn microcoil so that app roximately 1 nL of the sample was present in the sensitive region of t he microcoil. The microcoil was fabricated on a gallium arsenide subst rate with an inner diameter of 60 mu m, an outer diameter of 200 mu m, trace width of 10 mu m, trace spacing of 10 mu m, and trace height of 3 mu m. At 5.9 T (250 MHz) in H-1-NMR microspectroscopy experiments u sing a spectral width of 1 kHz, 4096 sampled data points, and a recove ry delay of 1 s, a SNR of 25 (per acquisition) and a spectral linewidt h of less than 2 Hz were obtained from a sample of water. These result s demonstrate that planar microcoils can be used for high-resolution N MR microspectroscopy. Such coils may also be suitable for localized NM R studies at the cellular level and as detectors in capillary electrop horesis or microbore liquid chromatography.