High-Sensitivity NMR Probe Systems

Abstract

Nuclear magnetic resonance (NMR) has become the method of choice for many types of applications. Still, sensitivity is a limiting factor in the applicability ofNMR, leading to long measurement times in advanced multidi- mensional experiments, and becoming prohibitive when very limited sample quantities are available. This lowsen- sitivity is mostly an intrinsic consequence of the low en- ergy scale of the nuclear moment in a static field, when compared to other thermodynamic energies like kBT. The commercial developments are mostly aimed at an increase in the static field and simultaneously a reduction of the noise using cryocooled detection coils. Current research shows a number of interesting developments toward the enhancement of the nuclear polarization by optical pump- ing or by transfer from the electronic bath in dynamic nuclear polarization (DNP) experiments. A more techno- logical approach is based on the miniaturization of the RF coils. In the next decade, one may expect the advent of the lab on a chip with in situ chemical processing and NMR analysis capabilities. A brave new method to improve detection sensitivity is based on very sensitive micromechanical force detectors. Recently, itwas demon- strated that the low-temperature force detection sensitiv- ity is sufficient to detect the magnetic moment of a single (electron) spin. These developments show that the NMR detection limits in terms of absolute sensitivity or imaging resolution are still open to significant improvements.