PNNL

Abstract

We present the numerical optimization and experimental characterization of two microstrip-based nuclear magnetic resonance (NMR) detectors. The first detector, introduced in our previous work, was a flat wire detector with a strip resting on a substrate,1 and the second detector was created by adding a ground plane on top of the strip conductor, separated by a sample-carrying capillary and a thin layer of insulator. The dimensional parameters of the detectors were optimized using numerical simulations with regards to radio frequency (RF) sensitivity and homogeneity, with particular attention given to the effect of the ground plane. The influence of copper surface finish and substrate surface on the spectral resolution was investigated, and a resolution of 0.8 – 1.5 Hz was obtained on 1 nL dionized water depending on sample positioning. For 0.13 nmol sucrose (0.2 M in 0.63 nL H2O) encapsulated between two Fluorinert plugs, high RF homogeneity (A810°/A90° = 70 – 80%) and high sensitivity (expressed in the limit of detection nLOD_m=0.73-1.21 nmol s^(1/2)) were achieved, allowing for high-performance 2D NMR spectroscopy of subnanoliter samples. The results reported here represent the first demonstration of high-resolution NMR spectroscopy at this size scale without the use of specialized pulse sequences to preserve spectral resolution.