NMR spiral surface microcoils: Design, fabrication, and imaging

NMR investigation of volume-limited chemical and biological samples requires a radio frequency (RF) microcoil with high signal-to-noise ratio (SNR) over the region of interest. Conventional approaches using solenoidal microcoils provide high sensitivity (RF field strength per unit current) and spectral resolution but require the sample and sample container to be enclosed by the coil. Planar surface microcoils provide an alternative configuration that allows direct access to the sample, but with the sacrifice of RF field uniformity. In this study we evaluate a family of planar RF microcoils (500 MHz, Archimedean geometry, 1-6 turns, inner radius 0.75 to 4 mm, and conductor widths of 75, 100, and 200 mum). The design, fabrication, and performance (electrical and NMR) of the coils are described. This coil configuration exhibits a high local SNR, easy fabrication, good electrical properties, and moderate spectral uniformity (suitable for imaging and low resolution NMR spectroscopy). This design can also be scaled to smaller dimensions. These results suggest that planar spiral RF microcoils will find applications in multimodality microscopy and microfludic devices where sample manipulation and coil integration with the microanalysis systems is necessary. (C) 2003 Wiley Periodicals, Inc.