Proton NMR spectroscopy at 7 Tesla (7T) was evaluated as a new method to quantify human fat composition noninvasively. In validation experiments, the composition of a known mixture of triolein, tristearin, and trilinolein agreed well with measurements by 1 H NMR spectroscopy. Triglycerides in calf subcutaneous tissue and tibial bone marrow were examined in 20 healthy subjects by 1 H spectroscopy. Ten well-resolved proton resonances from triglycerides were detected using stimulated echo acquisition mode sequence and small voxel (?0.1 ml), and T 1 and T 2 were measured. Triglyceride composition was not different between calf subcutaneous adipose tissue and tibial marrow for a given subject, and its variation among subjects, as a result of diet and genetic differences, fell in a narrow range. After correction for differential relaxation effects, the marrow fat composition was 29.1 6 3.5% saturated, 46.4 6 4.8% monounsaturated, and 24.5 6 3.1% diunsaturated, compared with adipose fat composition, 27.1 6 4.2% saturated, 49.6 6 5.7% monounsaturated, and 23.4 6 3.9% diunsaturated. Proton spectroscopy at 7T offers a simple, fast, noninvasive, and painless method for obtaining detailed information about lipid composition in humans, and the sensitivity and resolution of the method may facilitate longitudinal monitoring of changes in lipid composition in response to diet, exercise, and

The detection of biological molecules and their interactions is a significant component of modern biomedical research. In current biosensor technologies, simultaneous detection is limited to a small number of analytes by the spectral overlap of their signals. We have developed an NMR-based xenon biosensor that capitalizes on the enhanced signal-to-noise, spectral simplicity, and chemical-shift sensitivity of laser-polarized xenon to detect specific biomolecules at the level of tens of nanomoles. We present results using xenon ''functionalized'' by a biotin-modified supramolecular cage to detect biotin-avidin binding. This biosensor methodology can be extended to a multiplexing assay for multiple analytes.R ecent biosensor technologies exploit surface plasmon resonance (1), fluorescence polarization (2), and fluorescence resonance energy transfer (3) as detection methods. Although the sensitivity of such techniques is excellent, extending these assays to multiplexing capabilities has proven challenging because of the difficulty in distinguishing signals from different binding events. Although NMR spectroscopy is able to finely resolve signals from different molecules and environments, the spectral complexity and low sensitivity of NMR spectroscopy normally preclude its use as a detector of molecular targets in complex mixtures. Notable successes (4, 5) in the application of NMR to such problems are still limited by long acquisition times or a limited number of detectable analytes. Laser-polarized xenon NMR benefits from good signal-to-noise and spectral simplicity with the added advantage of substantial chemical-shift sensitivity.Optical pumping (6) has enhanced the use of xenon as a sensitive probe of its molecular environment (7,8). Laserpolarized xenon is being developed as a diagnostic agent for medical magnetic resonance imaging (9) and spectroscopy (10) and as a probe for the investigation of surfaces and cavities in porous materials and biological systems. Xenon provides information both through direct observation of its NMR spectrum (11)(12)(13)(14)(15)(16)(17) and by the transfer of its enhanced polarization to surrounding spins (18,19). In a protein solution, weak xenonprotein interactions render the chemical shift of xenon dependent on the accessible protein surface and even allow the monitoring of the protein conformation (20). To use xenon as a specific sensor of molecules, it would be valuable to ''functionalize'' the xenon for the purpose of reporting specific interactions with a molecular target.In this report, we demonstrate an example of such a functionalized system that exhibits molecular target recognition. Fig. 1 shows the chemical principle used for our initial study, a biosensor molecule designed to bind both xenon and protein.The molecule consists of three parts: the cage, which contains the xenon; the ligand, which directs the functionalized xenon to a specific protein; and the tether, which links the ligand and the cage. The ligand and target can be any two molecules or constructs. In su...