Nuclear magnetic resonance (NMR) spectroscopy device

Abstract

The invention relates to a Nuclear Magnetic Resonance (NMR) spectroscopy device adapted for carrying out 1D and nD homo- and heteronuclear NMR spectroscopy measurements of a plurality of nuclei, comprising an RF coil adapted to transmit RF to and/or receive RF from a measuring volume, wherein the RF coil forms part of a non-tuned radiofrequency circuit. The invention further relates to a method of NMR data acquisition, a method of manufacturing a NMR spectroscopy device and a NMR-device holder.

Claims

1. A Nuclear Magnetic Resonance (NMR) spectroscopy device for carrying out one dimensional and/or multidimensional heteronuclear spectroscopy measurements of a plurality of nuclides, the NMR spectroscopy device comprising: a magnet for maintaining a substantially constant magnetic field in a measuring volume; and a fluidic device, including a chip substrate, wherein a micro-coil is provided on the chip substrate, the micro-coil being an RF coil adapted to transmit RF radiation to and/or receive RF radiation from the measuring volume, wherein the micro-coil connects to and forms part of a non-tuned non-matched radiofrequency circuit.

2. The NMR spectroscopy device according to claim 1, wherein the RF coil has a detection volume of less than 1 milliliter.

3. The NMR spectroscopy device of claim 2, wherein the detection volume is less than 100 microliters.

4. The NMR spectroscopy device of claim 3, wherein the detection volume is less than 100 nanoliters.

5. A method of carrying out Nuclear Magnetic Resonance (NMR) one dimensional and/or multidimensional heteronuclear spectroscopy measurements of a plurality of nuclides, the method comprising the steps of: providing a sample comprising a plurality of nuclides in the measuring volume of the NMR spectroscopy device of claim 1: executing a data acquisition sequence on the NMR spectroscopy device; acquiring data from the sample pursuant to said data acquisition sequence.

6. The method according to claim 5, wherein the data acquisition sequence includes decoupling on one of the nuclides' Larmor frequencies.

7. The NMR spectroscopy device of claim 1, further comprising holder configured for allowing the hosting of the fluidics device, said holder comprising a first side and a second side, wherein the first side is provided with a non-tuned RF circuit having electrodes for connecting to the fluidic device; and the second side is provided with fluidic connection points, wherein the holder is manufactured from a non-magnetic material.

8. The NMR-device holder according to claim 7, comprising first holes and second holes, the first holes correspond to the electrodes on the first side and the second holes correspond to fluidic connection points on the second side.

9. The NMR spectroscopy device of claim 7, wherein the holder is manufactured from aluminum.

10. The NMR spectroscopy device of claim 1, wherein the micro-coil is a spiral coil.

11. The NMR spectroscopy device of claim 1, further comprising a sample inlet/outlet provided on the chip substrate.

12. The NMR spectroscopy device of claim 11, wherein a fluidic channel, configured to dwell in the measuring volume, is centered on the chip substrate.

13. The NMR spectroscopy device of claim 11, wherein the micro-coil is positioned on a bottom of the chip substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 presents in a schematic way an embodiment of an NMR device according to an aspect of the invention.

(2) FIG. 2 presents seven spectra for seven different nuclides comprised in the same sample which have been acquired using the device of FIG. 1.

(3) FIG. 3 presents in a schematic way an example of .sup.13C spectra acquired for different NOE and/or decoupling schemes.

(4) FIG. 4 presents in a schematic way an embodiment of .sup.1H-.sup.13C-HSQC spectra obtained from neat acetic acid-2-.sup.13C.

(5) FIG. 5 presents in a schematic way an embodiment of .sup.19F spectra.

(6) FIG. 6 presents in a schematic way an embodiment of .sup.19F.sup.31P-HSQC spectra.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIG. 1 presents in a schematic way an embodiment of a NMR device according to an aspect of the invention. In view “a” a top view of the device is presented.

(8) In a particular embodiment of the device 10 according to the invention, a 32-turn microcoil may have a low resistance (ρ=7Ω) and may be connected directly to a coaxial cable without any tuning/matching circuit. It is found that such arrangement is technically meaningful for the following reasons.

(9) First, a spiral coil, like a coaxial cable, can be shown to have broad-band characteristics and its impedance is remaining close to its DC value in the frequency range between 0 MHz up to about 500 MHz or more.

(10) Secondly, the current passed from an RF source through a coaxial cable in a resistor R remains finite even when R tends to zero, despite the fact that the transmitted power also tends to zero due to power reflection.

(11) Thirdly, the capability of the RF pulse to produce the oscillating excitation magnetic field B.sub.1 (to be superposed on the constant magnetic field B.sub.0 in the measuring volume) depends upon the transmitted current and not the transmitted power. It will be appreciated that usually the B.sub.1 filed is orthogonal to the B.sub.0 field. The B.sub.1 field is in fact proportional to the current, and inversely proportional to the sample-to-coil distance. It has been found, both computationally and empirically, that the current passed through the unmatched (non-tuned) coil set-up is sufficient to produce a very usable B.sub.1 excitation field in the measuring volume across the full frequency range, as is schematically depicted in the nutation experiments at .sup.2H, .sup.19F and .sup.1H Larmor frequencies, see view “d” in FIG. 1. Once a reasonable value of B.sub.1 is reached, the same set-up has also close-to-optimal detection efficiency due to the reciprocity theorem, described in Hoult, D. I. The principle of reciprocity in signal strength calculations—A mathematical guide. Concepts in Magnetic Resonance 12, 173-187 (2000). It is further found that during signal reception a low-impedance coil can in fact easily drive a 50Ω coaxial cable and load. Moreover, a further advantageous phenomenon is detected—the low impedance of the coil minimizes its Johnson noise.

(12) .sup.1H and .sup.19F, being so-called high-frequency nuclides, are widely addressed with NMR spectroscopy because of their relatively high sensitivity. It is found that with the device according to the invention detection of nuclides having low gyromagnetic ratios may be enabled. For example, it is found that with the device according to the invention NMR spectroscopy of .sup.2H, .sup.13C, .sup.15N, .sup.31P, .sup.7Li, .sup.11B, .sup.29Si is possible. In general, direction of nuclides of importance for biomolecular science, organic chemistry, bio- or inorganic chemistry, or material studies may be enabled with the device according to the invention.

(13) Preferably, the device according to the invention is embodied as an insert into a standard magnetic resonance apparatus. This has an advantage that the magnet for providing the constant B.sub.0 field may be avoided as the B.sub.0 field of the NMR apparatus may be readily used.

(14) View “b” of FIG. 1 presents in a schematic way an embodiment of a fluidic device 10a according to the invention. A suitable sample inlet/outlet 2 may be provided on a chip substrate 3. A fluidic channel 4 adapted to dwell in the measuring volume of the device 10a is preferably centered on the substrate 3. The coil 6 may be arranged on the bottom of the substrate 3, having typically between 1 and 50 turns. It will be appreciated that a suitable plurality of the copper electrodes 5 may be envisaged. It will be appreciated that a suitable plurality of coils 6 may be envisaged. The copper electrodes are preferably provided using suitable lithographic method. An equivalent electrical circuit of the device 10a is schematically presented in view “c”.

(15) It is found that the device according to the invention enables carrying out of the NMR experiments at any particular static magnetic field strength (B.sub.0). More in particular, the data acquisition sequence may comprise sequences for heteronuclear 1D and nD experiments and/or sequences including decoupling with the Larmor frequency of a nuclide coupled to the direct-detected nuclide.

(16) FIG. 2 presents seven spectra for seven different nuclides comprised in the same sample which have been acquired using the device of FIG. 1. In order to demonstrate the broad-band character of the device according to the invention, spectra of seven different nuclides present in the same sample were sequentially recorded in the 400-61 MHz frequency range, measuring, consecutively .sup.1H, .sup.19F, .sup.31P, .sup.7Li, .sup.11B, .sup.23Na and .sup.2H.

(17) The good operational performance of the device according to the invention is illustrated by the 30 kHz wide .sup.19F NMR spectrum showing the BF.sub.4 and PF.sub.6 anion signals, the latter appearing to the same coupling constant observed in the doublet with characteristic .sup.1J.sub.PF coupling of 710 Hz, corresponding to the same coupling constant observed in the multiplet in the .sup.31P spectrum.

(18) It is found that the signal to noise ratio of the RF coil forming part of a non-tuned circuit used in the device according to the invention is comparable to the signal to noise ratio found in the state of the art coils used in tuned circuits. In accordance with an aspect of the invention the NMR spectroscopy device may comprise a plurality of coils, which may be adapted to be addressed sequentially and/or contemporaneously. More in particular, the said plurality of coils can be part of a non-tuned radiofrequency circuit, or wherein at least one of the said plurality of coils is part of the non-tuned radiofrequency circuit. In the latter configuration one or more of the remaining coils may be tuned to a particular Larmor frequency.

(19) Less NMR-sensitive nuclides, such as .sup.13C, are generally detected using indirect-detection techniques in which the spectral information of the less-sensitive nuclide is recovered from its effect on the more sensitive nuclide, assuming they are coupled. To carry out such experiments one must generally employ different probes or a special probe containing separate coils and/or tuning and matching circuits for the individual nuclides to be addressed.

(20) The broad-band nature of the device according to the invention enables execution of ubiquitously employed heteronuclear 2D NMR experiments, with the single non-tuned NMR coil addressing frequencies of different nuclides, having Larmor frequencies separated by hundreds of MHz. Most popular 2D experiments include HSQC (heteronuclear single-quantum coherence) and HMBC (heteronuclear multiple-bond coherence) experiments, performed to assign the proton-carbon backbone of organic molecules. The good performance and straightforward handling of the non-tuned coil set-up has been proven by inventors carrying out the full set of per se standard experiments, such as .sup.1H.sup.1H-COSY, .sup.1H.sup.1H-NOESY, .sup.1H.sup.13C-HSQC and .sup.1H.sup.13C-HMBC, performed on a 18 μg sample of ethylcinnamate. The heteronuclear 2D experiments with the device according to the invention permit full assignment of all .sup.1H and .sup.13C signals at natural abundance levels of these isotopes.

(21) As a further illustration of the capabilities of the device according to the invention .sup.19F measurements may be performed for samples from medicinal chemistry, polymers, agrochemistry, MRI contrast agents.

(22) .sup.1H.sup.13C-HSQC, .sup.1H.sup.13C-HMBC, .sup.19F.sup.13C-HSQC, .sup.19F.sup.13C-HMBC measurements have been carried out on a trifluoroethanol sample using the device according to the invention. The acquired data demonstrated detailed information on all the one-bond, two-bond and three-bond coupling constants. Particularly informative are the cross peaks in the HMBC spectra, which show complex multiplet patterns that are both skewed but in opposite directions attributable to the fact that the .sup.19F-.sup.13C and .sup.1H-.sup.13C coupling constants have opposite signs. It has been demonstrated that the device according to the invention is capable of providing similar results in terms of quality and sensitivity compared to the conventional (tuned) systems.

(23) In addition, it is found that the device according to the invention is particularly suitable for carrying out measurements targeting urinary excretion of taurine. Still in addition, a direct detection of the trifluoromethylphenol is possible using the device according to the invention due to its high sensitivity to .sup.19F. A detection limit of about 100 picomole is found to be feasible for the device according to the invention.

(24) Summarizing, a front end of the device according to the invention comprising a (micro)coil-on a chip terminating a coaxial cable with no tuning and matching circuitry functions as a high-resolution versatile coil NMR system with broad-band character enabling execution of mono- and multi-dimensional heteronuclear data acquisition.

(25) The device according to the invention may be used in medical applications, in forensic studies, in measuring (neat) biofluids without using additives or deuterated solvents, which are usually compulsory in the state of the art NMR spectroscopic systems.

(26) The device according to the invention may be embodied as an insert into a magnetic resonance apparatus, or may be used as a stand-alone portable or table-top system. The device according to the invention may further be integrated with other lab-on-chip platforms supporting different applications for on-line monitoring of chemical reactions or for enabling rapid analysis of biological fluids.

(27) FIG. 3 presents in a schematic way an example of .sup.13C spectra acquired for different decoupling schemes. Each experiment was acquired with 128 scans, total acquisition time was about 9 minutes.

(28) The presented spectra are obtained from neat acetic acid-2-13C, using the following decoupling schemes: 1) spectrum 1 is acquired with no decoupling; 2) spectrum 2 is acquired with no decoupling with NOE enhancement; 3) spectrum 3 is acquired with NOE enhancement; 4) spectrum 4 is acquired with decoupling and NOE enhancement.

(29) It will be appreciated that different NOE enhancement schemes may be envisaged. For example, a Steady State may be used. In this mode a single resonance is saturated at low power before acquiring the FID. Alternatively, a truncated driven NOE (TOE) may be envisaged. This mode is as Steady State, but is saturated for various shorter times so the buildup of NOE can be observed. Still alternatively, Transient NOE may be envisaged. In this mode a single resonance may be selectively inverted or all resonances may be frequency labeled by a 90 degree pulse and a variable delay. The NOE acquisition mode is known per se and will not be explained in further details.

(30) FIG. 4 presents in a schematic way an embodiment of .sup.1H-.sup.13C spectra obtained from neat acetic acid-2-.sup.13C. In this embodiment .sup.1H-.sup.13C HSQC coupled acquisition (see item 41), 16 increments in the indirect detection and 4 scans per increment was carried out, acquisition time 3 minutes.

(31) Spectrum 42 relates to a decoupled acquisition, wherein 8 increments in the indirect detection and 4 scans per increment were used, the acquisition time was 2 minutes.

(32) FIG. 5 presents in a schematic way an embodiment of .sup.19F spectra. The source was 1M NaPF.sub.6 dissolved in water. Spectrum (1) shows coupled results while spectrum (2) shows decoupled results.

(33) FIG. 6 presents in a schematic way an embodiment of .sup.19F.sup.31P spectra. Items 61 depict .sup.19F.sup.31P-HSQC coupled acquisition, 8 increments in the indirect detection and 8 scans per increment, acquisition time 3 minutes. Item 62 depicts a decoupled acquisition, 8 increments in the indirect detection and 8 scans per increment, acquisition time 3 minutes. The source was 1M NaPF.sub.6 dissolved in water.

(34) While specific embodiments have been described above, it will be appreciated that the invention may be practiced otherwise than as described. Moreover, specific items discussed with reference to any of the isolated drawings may freely be inter-changed supplementing each outer in any particular way. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described in the foregoing without departing from the scope of the claims set out below.