Magic-angle Coil Spinning Research Articles

Monolithic MACS micro resonators

Magic Angle Coil Spinning (MACS) aids improving the intrinsically low NMR sensitivity of heterogeneous microscopic samples. We report on the design and testing of a new type of monolithic 2D MACS resonators to overcome known limitations of conventional micro coils. The resonators’ conductors were printed on dielectric substrate and tuned without utilizing lumped element capacitors. Self-resonance conditions have been computed by a hybrid FEM-MoM technique. Preliminary results reported here indicate robust mechanical stability, reduced eddy currents heating and negligible susceptibility effects. The gain in B1/P is in agreement with the NMR sensitivity enhancement according to the principle of reciprocity. A sensitivity enhancement larger than 3 has been achieved in a monolithic micro resonator inside a standard 4mm rotor at 500MHz. These 2D resonators could offer higher performance micro-detection and ease of use of heterogeneous microscopic substances such as biomedical samples, microscopic specimens and thin film materials.

(1)H high resolution magic-angle coil spinning (HR-MACS) μNMR metabolic profiling of whole Saccharomyces cervisiae cells: a demonstrative study.

The low sensitivity and thus need for large sample volume is one of the major drawbacks of Nuclear Magnetic Resonance (NMR) spectroscopy. This is especially problematic for performing rich metabolic profiling of scarce samples such as whole cells or living organisms. This study evaluates a 1H HR-MAS approach for metabolic profiling of small volumes (250 nl) of whole cells. We have applied an emerging micro-NMR technology, high-resolution magic-angle coil spinning (HR-MACS), to study whole Saccharomyces cervisiae cells. We find that high-resolution high-sensitivity spectra can be obtained with only 19 million cells and, as a demonstration of the metabolic profiling potential, we perform two independent metabolomics studies identifying the significant metabolites associated with osmotic stress and aging.

μHigh resolution-magic-angle spinning NMR spectroscopy for metabolic phenotyping of Caenorhabditis elegans.

Analysis of model organisms, such as the submillimeter-size Caenorhabditis elegans, plays a central role in understanding biological functions across species and in characterizing phenotypes associated with genetic mutations. In recent years, metabolic phenotyping studies of C. elegans based on (1)H high-resolution magic-angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy have relied on the observation of large populations of nematodes, requiring labor-intensive sample preparation that considerably limits high-throughput characterization of C. elegans. In this work, we open new platforms for metabolic phenotyping of C. elegans mutants. We determine rich metabolic profiles (31 metabolites identified) from samples of 12 individuals using a (1)H NMR microprobe featuring high-resolution magic-angle coil spinning (HR-MACS), a simple conversion of a standard HR-MAS probe to μHR-MAS. In addition, we characterize the metabolic variations between two different strains of C. elegans (wild-type vs slcf-1 mutant). We also acquire a NMR spectrum of a single C. elegans worm at 23.5 T. This study represents the first example of a metabolomic investigation carried out on a small number of submillimeter-size organisms, demonstrating the potential of NMR microtechnologies for metabolomics screening of small model organisms.

Refined Magic-Angle Coil Spinning Resonator for Nanoliter NMR Spectroscopy: Enhanced Spectral Resolution

The magic-angle coil spinning (MACS) resonator allows a simple approach for nanoliter nuclear magnetic resonance (NMR) detections with enhanced sensitivity and high-resolution under sample magic-angle spinning (MAS). Currently, the spectral resolution acquired with MACS is not efficient for detailed characterization of semisolids like biopsies, where subhertz resolution is necessary. Here, we describe the two sources of line broadening from MACS, sample temperature gradient and anisotropic magnetic susceptibility, and present a refined high-resolution magic-angle coil spinning (HR-MACS) resonator that improves the spectral resolution. We demonstrate with the high quality HR-MACS NMR spectra of micronematodes and tissue biopsy, and illustrate its potential for NMR-based metabolomics of nanoliter tissue samples.

Microfabricated Inserts for Magic Angle Coil Spinning (MACS) Wireless NMR Spectroscopy

This article describes the development and testing of the first automatically microfabricated probes to be used in conjunction with the magic angle coil spinning (MACS) NMR technique. NMR spectroscopy is a versatile technique for a large range of applications, but its intrinsically low sensitivity poses significant difficulties in analyzing mass- and volume-limited samples. The combination of microfabrication technology and MACS addresses several well-known NMR issues in a concerted manner for the first time: (i) reproducible wafer-scale fabrication of the first-in-kind on-chip LC microresonator for inductive coupling of the NMR signal and reliable exploitation of MACS capabilities; (ii) improving the sensitivity and the spectral resolution by simultaneous spinning the detection microcoil together with the sample at the “magic angle” of 54.74° with respect to the direction of the magnetic field (magic angle spinning – MAS), accompanied by the wireless signal transmission between the microcoil and the primary circuit of the NMR spectrometer; (iii) given the high spinning rates (tens of kHz) involved in the MAS methodology, the microfabricated inserts exhibit a clear kinematic advantage over their previously demonstrated counterparts due to the inherent capability to produce small radius cylindrical geometries, thus tremendously reducing the mechanical stress and tearing forces on the sample. In order to demonstrate the versatility of the microfabrication technology, we have designed MACS probes for various Larmor frequencies (194, 500 and 700 MHz) testing several samples such as water, Drosophila pupae, adamantane solid and LiCl at different magic angle spinning speeds.

Slow magic‐angle coil spinning: A high‐sensitivity and high‐resolution NMR strategy for microscopic biological specimens

High-resolution magic-angle spinning has become a valuable tool to study biologic samples; however, there are only a few high-resolution magic-angle spinning methodologies that have been explored specifically to deal with small semisolid biomaterials such as tissues. Here, we report a novel high-resolution (1)H NMR spectroscopic approach using magic-angle coil spinning. We demonstrate its potential for intact tissues by combining a resonant microcoil with a large-volume commercial magic-angle spinning rotor, where the microcoil offers incredible sensitivity and the large-volume magic-angle spinning rotor provides stable slow magic-angle spinning. This approach provides high-resolution spectra with high sensitivity and the preservation of living biologic specimens for an accurate chemical analysis.

Double-resonance magic angle coil spinning

We present an extension of magic angle coil spinning (MACS) solid-state NMR spectroscopy to double-resonance experiments, enabling implementation of powerful double-resonance solid-state NMR methodologies including cross polarization, proton decoupling, and two-dimensional correlation spectroscopy etc., while still enjoying the merits that are intrinsic to MACS, such as high concentration sensitivity, eliminated magnetic susceptibility-induced field distortion, and an easy-to-use approach with the conventional and widespread hardware.

Experimental and numerical examination of eddy (Foucault) currents in rotating micro-coils: Generation of heat and its impact on sample temperature

The application of nuclear magnetic resonance (NMR) to systems of limited quantity has stimulated the use of micro-coils (diameter <1mm). One method recently proposed for the union of micro-coils with Magic Angle sample Spinning (MAS), involves the integration of a tuned micro-coil circuit within standard MAS rotors inductively coupled to the MAS probe coil, termed “magic-angle coil spinning” (MACS). The spinning of conductive materials results in the creation of circulating Foucault (eddy) currents, which generate heat. We report the first data acquired with a 4mm MACS system and spinning up to 10kHz. The need to spin faster necessitates improved methods to control heating. We propose an approximate solution to calculate the power losses (heat) from the eddy currents for a solenoidal coil, in order to provide insight into the functional dependencies of Foucault currents. Experimental tests of the dependencies reveal conditions which result in reduced sample heating and negligible temperature distributions over the sample volume.