Evaluation of double-tuned single-sided planar microcoils for the analysis of small 13 C enriched biological samples using 1 H-13 C 2D heteronuclear correlation NMR spectroscopy.

Microcoils provide a cost-effective approach to improve detection limits for mass-limited samples. Single-sided planar microcoils are advantageous in comparison to volume coils, in that the sample can simply be placed on top. However, the considerable drawback is that the RF field that is produced by the coil decreases with distance from the coil surface, which potentially limits more complex multi-pulse NMR pulse sequences. Unfortunately, 1 H NMR alone is not very informative for intact biological samples due to line broadening caused by magnetic susceptibility distortions, and 1 H-13 C 2D NMR correlations are required to provide the additional spectral dispersion for metabolic assignments in vivo or in situ. To our knowledge, double-tuned single-sided microcoils have not been applied for the 2D 1 H-13 C analysis of intact 13 C enriched biological samples. Questions include the following: Can 1 H-13 C 2D NMR be performed on single-sided planar microcoils? If so, do they still hold sensitivity advantages over conventional 5 mm NMR technology for mass limited samples? Here, 2D 1 H-13 C HSQC, HMQC, and HETCOR variants were compared and then applied to 13 C enriched broccoli seeds and Daphnia magna (water fleas). Compared to 5 mm NMR probes, the microcoils showed a sixfold improvement in mass sensitivity (albeit only for a small localized region) and allowed for the identification of metabolites in a single intact D. magna for the first time. Single-sided planar microcoils show practical benefit for 1 H-13 C NMR of intact biological samples, if localized information within ~0.7 mm of the 1 mm I.D. planar microcoil surface is of specific interest.

A CMOS NMR needle for probing brain physiology with high spatial and temporal resolution.

Magnetic resonance imaging and spectroscopy are versatile methods for probing brain physiology, but their intrinsically low sensitivity limits the achievable spatial and temporal resolution. Here, we introduce a monolithically integrated NMR-on-a-chip needle that combines an ultra-sensitive 300 µm NMR coil with a complete NMR transceiver, enabling in vivo measurements of blood oxygenation and flow in nanoliter volumes at a sampling rate of 200 Hz.

Rapid Chemical Reaction Monitoring by Digital Microfluidics-NMR: Proof of Principle Towards an Automated Synthetic Discovery Platform.

Microcoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub-microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF-NMR. The study represents a key first step towards larger DMF-NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time.

NMR spectroscopy of single sub-nL ova with inductive ultra-compact single-chip probes.

Nuclear magnetic resonance (NMR) spectroscopy enables non-invasive chemical studies of intact living matter. However, the use of NMR at the volume scale typical of microorganisms is hindered by sensitivity limitations, and experiments on single intact organisms have so far been limited to entities having volumes larger than 5 nL. Here we show NMR spectroscopy experiments conducted on single intact ova of 0.1 and 0.5 nL (i.e. 10 to 50 times smaller than previously achieved), thereby reaching the relevant volume scale where life development begins for a broad variety of organisms, humans included. Performing experiments with inductive ultra-compact (1 mm2) single-chip NMR probes, consisting of a low noise transceiver and a multilayer 150 µm planar microcoil, we demonstrate that the achieved limit of detection (about 5 pmol of 1H nuclei) is sufficient to detect endogenous compounds. Our findings suggest that single-chip probes are promising candidates to enable NMR-based study and selection of microscopic entities at biologically relevant volume scales.