Noise detected two dimensional NMR

Spin noise, the random fluctuation of atomic magnetic moments has developed into an important source of spectroscopic and imaging information in the last decade. The main aim of the pertinent proposal is to establish methods that exploit transverse nuclear spin noise for indirect detection in NMR spectroscopy. While existing methods relying on the detection of longitudinal spin noise are mainly used for magnetic resonance force microscopy (MRFM) on solid samples, we target spectroscopy of liquid samples. The resonance frequencies determined from transverse spin noise contains chemically relevant information, like chemical shifts and coupling constants. The experiments will be developed and implemented on state-of-the-art commercial NMR- spectrometers. Two distinct approaches to achieve this general goal will be pursued here: (1) detection of spin noise based on noise correlation and (2) stochastic coherence transfer effected by spin noise. In the first approach, based on previous work on detecting longitudinal magnetization fluctuations by the group of Weitekamp in the context of MRFM, we will use correlation experiments to distinguish purely random for correlated noise. Radio frequency pulses will be used to transfer coherence between two noise detection periods. Noise detected analogs of twodimensional pulse NMR experiments will thus become possible. For the second approach nuclear spin noise itself will be exploited for inducing coherence transfer between spins. To circumvent low sensitivity problems due to the low probability of the correlation of two noise events, we will initially not target pure 2D noise spectroscopy (i.e. an entirely rf-pulse-less scheme), but try a hybrid approach by exciting an initial coherence through a single radio frequency pulse. Special software needs to be developed for the processing of the data acquired by both methods. The proposed NMR methods will lay the foundation for various kinds of novel NMR experiments, applicable to spin systems in situations, where pulse excitation is either unpractical (e.g. extreme spectral widths, or in locations where no external radio frequency can be applied) or when the spin equilibrium should not be disturbed, like in cases of extremely long relaxation times. These developments shall establish indirect noise detection in NMR as an adequate tool to investigate diverse samples in materials science, catalysis, and biochemistry at different, in particular for much smaller (nano) scales and under extreme conditions.

We have achieved first proof of principle for spin noise detected multi-dimensional nuclear magnetic resonance (NMR) spectroscopy and have made substantial improvements in the data acquisition and processing schemes, which will enable one to carry NMR spectroscopy to the nanoscale. NMR spectroscopy and magnetic resonance imaging (MRI) provide non-invasive information about multiple nuclear species in bulk matter, with wide-ranging applications from basic physics and chemistry to biomedical imaging. Ability to probe many different magnetic nuclei such as 1H, 15N, 13C, 31P etc and differentiate their chemical and spatial positions gives an opportunity to elucidate the structure of different biomolecules by NMR spectroscopy and imaging by MRI. The major advantages of NMR comprise the non-invasive nature and to characterize molecules under physiological conditions and in some case even in cellular environment. The long term goal is to take such powerful technique to nanoscale level, which bears the prospect of multiplying its application potential. In that regime, which is way beyond current routine NMR application, noise magnetization dominates over polarized magnetization. We have used the transverse components of spin noise using cryoprobe at high field on a state-of-the art commercial NMR spectrometer to detect multidimensional NMR through spin noise. Although our demonstration experiment is ca. 108 times less sensitive than corresponding conventional (pulsed) NMR experiments, this ratio improves dramatically considering the potential of appropriate miniaturization of the sample an the NMR instrumentation in the future. The experimental data acquisition and processing algorithms designed over the course of this project, already now allow us to develop methods that will work on future miniaturized and optimized hardware at the nonoscopic scale.