Device for the NMR Analysis of Substances in a Sample, Respiratory Gas Analysis Device, Fuel Sensor and Method

Abstract

A device for analyzing substances in a sample on the basis of a measurement of nuclear magnetic resonances including a magnetic field device configured to generate a magnetic field. The device is configured such that, in order to detect magnetic resonances induced in the sample by the generation of the magnetic field, provision is made of at least one magnetic field sensor which comprises at least one sensitive component with diamond structures. The diamond structures have nitrogen vacancy centers.

Claims

1. A device for analysis of substances in a sample based on a measurement of magnetic nuclear spin resonances, comprising: a magnetic field device configured to generate a magnetic field; and at least one magnetic field sensor configured to detect magnetic resonances induced in the sample by of the magnetic field, the at least one magnetic field sensor including at least one sensitive component having diamond structures, the diamond structures including nitrogen vacancy centers.

2. The device as claimed in claim 1, wherein the at least one magnetic field sensor further includes at least one first electromagnetic device configured to introduce electromagnetic excitation radiation in an optical range, at least one second electromagnetic device configured to introduce electromagnetic radiation in a microwave range, and at least one detection device configured to detect emitted fluorescence radiation.

3. The device as claimed in claim 2, wherein: the at least one magnetic field sensor further includes at least one filtering device configured to filter electromagnetic radiation, and the at least one filtering device includes at least one optical filter layer configured to filter the excitation radiation out of the emitted fluorescence radiation.

4. The device as claimed in claim 1, wherein: the at least one sensitive component is included in a plurality of sensitive components, the at least one magnetic field sensor further includes an arrangement of the plurality of sensitive components, and each sensitive component of the plurality of sensitive components is configured for individual evaluation.

5. The device as claimed in claim 1, wherein the at least one sensitive component has needle structures or tube structures configured for surface enlargement.

6. The device as claimed in claim 1, wherein the at least one sensitive component has capillary structures.

7. The device as claimed in claim 1, wherein the sensitive component has at least one Peltier element configured for heating and/or cooling.

8. The device as claimed in claim 1, further comprising: an ionization device configured to ionize substances in the sample.

9. The device as claimed in claim 1, further comprising: a generating device configured to generate a positive potential in the at least one sensitive component.

10. A method of analyzing substances in a sample based on measurement of magnetic nuclear spin resonances comprising: inducing magnetic resonances in the sample by generating a magnetic field; and detecting the induced magnetic resonances using diamond structures with nitrogen vacancy centers.

11. The method as claimed in claim 10, further comprising: evaluating fluorescence radiation emitted by the diamond structures as a measure of the induced magnetic resonances on introduction of electromagnetic radiation in an optical range and introduction of electromagnetic radiation in a microwave range.

12. A respiratory gas analysis device, comprising: an NMR device configured to analyze substances in a sample based on a measurement of magnetic nuclear spin resonances, the NMR device including (i) a magnetic field device configured to generate a magnetic field, and (ii) at least one magnetic field sensor configured to detect magnetic resonances induced in the sample by the magnetic field, the at least one magnetic field sensor including at least one sensitive component having diamond structures, the diamond structures including nitrogen vacancy centers.

13. The respiratory gas analysis device as claimed in claim 12, further comprising: a condensing device configured to condense exhaled respiratory air and to cool the sensitive component.

14. The respiratory gas analysis device as claimed in claim 12, wherein the respiratory gas analysis device is configured to measure hydrogen peroxide and/or hydrogen sulfide.

15. The device as claimed in claim 1, wherein the device is included in a fuel sensor.

16. The device as claimed in claim 2, wherein: the electromagnetic excitation radiation in the optical range has a wavelength range of 530 nm to 570 nm, and the electromagnetic radiation in the microwave range has a frequency range of 2000 MHz to 4000 MHz.

17. The method as claimed in claim 11, wherein: the electromagnetic radiation in the microwave range is introduced with varying frequency, and the method includes evaluating resulting minima in the fluorescence radiation emitted by the diamond structures in relation to the frequency of the electromagnetic radiation in the microwave range.

18. The respiratory gas analysis device as claimed in claim 13, wherein the condensing device is a cold trap.

Description

[0026] Further features and advantages of the invention will be apparent from the description of working examples which follows, in conjunction with the drawings. It is possible here for the individual features each to be implemented alone or in combination with one another.

[0027] The figures show:

[0028] FIG. 1 schematic diagram of a nitrogen vacancy center in diamond;

[0029] FIG. 2 schematic section diagram of an embodiment of an analysis device of the invention as a monolithically integrated NMR sensor element for use as a fuel quality sensor;

[0030] FIG. 3 schematic section diagram of a further embodiment of an analysis device of the invention as a monolithically integrated NMR sensor element for use in an analysis device; and

[0031] FIG. 4 schematic diagram of a respiratory gas analysis device of the invention.

DESCRIPTION OF WORKING EXAMPLES

[0032] The core of the invention is the exploitation of nitrogen vacancy centers in diamond for measurement of magnetic nuclear spin resonances, by means of which it is possible to provide very sensitive measurement devices which are especially also suitable for miniaturized applications.

[0033] FIG. 1 illustrates the nitrogen vacancy center (NV center), which is known per se, in diamond. What is shown is the carbon atom lattice that forms the diamond structure. One of the carbon atoms is replaced by a nitrogen atom N (arrow 1). A directly adjacent carbon atom is missing in the diamond lattice. This is identified in this diagram by V (vacancy) (arrow 2). Such an NV center in diamond has a particular energy spectrum at room temperature. In the normal state, i.e. on excitation with light in the optical range and without further irradiation in the microwave range and without application of a magnetic field, the NV center on optical excitation shows fluorescence in the red wavelength range. If, as well as the optical excitation, microwave radiation is additionally also introduced, there is a measurable drop in the fluorescence, i.e. a fluorescence minimum, at a particular frequency, especially at 2.88 GHz. This phenomenon can be explained in that the electrons of the NV center in this case are raised from the level m.sub.s=1 of the .sup.3A state to the level m.sub.s=1 of the .sup.3E state and thence recombine in a non-radiative manner. On application of an external magnetic field, there is splitting of the level m.sub.s=1 (Zeeman splitting), and, on application of the fluorescence across the frequency of the microwave excitation, two minima are observed in the fluorescence spectrum, the frequency separation of which is proportional to the magnetic field strength (Balasubramanian et al., Nature, vol. 455, page 648 (2008)). The magnetic field sensitivity is defined here by the minimum resolvable frequency shift and may reach up to 100 pT/Hz. When the microwave frequency corresponds to the energy separation between the level m.sub.s=0 and m.sub.s=1, there is thus a drop in the fluorescence. In the case of an external magnetic field, there is a split in the level m.sub.s=1, and two defined microwave frequencies at which the fluorescence decreases (minima) are observed. The frequency separation in the case of these defined microwave frequencies is proportional to the magnetic field, and so it is possible to infer the magnetic field strength by evaluation of the fluorescence minima.

[0034] Nuclear spin resonance spectroscopy, which is known per se, is based on the fact that many atoms or isotopes have a magnetic moment in their nuclear spin. These isotopes include the naturally occurring .sup.1H isotopes, for example in hydrogen peroxide (H.sub.2O.sub.2), and the .sup.13C isotope present in all organic compounds. These magnetic moments are aligned in a static manner without external excitation. Through application of an external magnetic field, these spins begin to precess and a magnetic alternating field with characteristic frequency occurs. The frequency can be assigned to the respective atomic species and the bonding state. The measurement principle underlying the invention detects the characteristic frequencies with the aid of a magnetic field sensor based on diamond structures with NV centers. The nuclear spin resonances are visible as noise in the fluorescence spectra of the NV centers. By specific pump-probe sequences, called XY8N decoupling sequences, it is possible to filter the nuclear spin resonances out of the noise. The analysis of these noise spectra then allows, as in conventional nuclear spin resonance spectroscopy, a chemical analysis of the sample constituents. It has already been shown by Staudacher et al. (Science, vol. 339, pages 561-563 (2013)) that, for example, both distinction between .sup.13C and .sup.1H and distinction of various substances is possible by the measurement principle of the invention.

[0035] FIG. 2 shows a possible embodiment of a monolithically integrated NMR sensor element of the invention as an analysis device 20 of the invention. Bonded to a carrier substrate 21, for example a silicon substrate, is an LED structure 22 with an integrated light source 33. Alternatively, rather than an LED structure, for example, a VCSEL laser chip may be provided. The light source 33 should preferably emit a wavelength in the green range of the visible light spectrum, especially in the wavelength range between about 530 nm and about 570 nm, since the photon absorption of the NV centers is at a maximum within this range. The carrier substrate 21 further comprises a photodiode 23, for example a p-n photodiode, or an arrangement of two or more photodiodes. Above the photodiode is an optical filter layer 24. Above the filter layer 24 is arranged a diamond layer 25 in admixture with NV centers as the sensitive component of the analysis device 20. In the spatial proximity of the diamond layer 25 is provided an RF antenna as means 26 of introducing the microwave radiation. In association with a voltage-controlled oscillator (VCO), the requisite electromagnetic excitation radiation in the microwave range can be introduced by the microwave antenna 26. The antenna 26 may, for example, be an RF strip antenna positioned at the edge of the photodiode array 23. In the case of simultaneous electromagnetic excitation radiation in the optical range by means of the light source 33, the characteristic nuclear spin resonances in the NV centers emit a characteristic fluorescence spectrum detectable via the photodiode 23. At the same time, the optical filter layer 24 filters the excitation light out of the fluorescence spectrum. The measurement signal which is then evaluated is the change in the fluorescence intensity on excitation with the pump-probe sequence (XY8N decoupling sequence).

[0036] Since the minimum resolvable frequency shift is connected to the lifetime of the excited spin states in the NV centers, it may be advantageous, for measurement of the nuclear spin resonances, to utilize the effect of coupling of NV electron spins to the N nuclear spin, and to transmit the frequency information to the N nuclear spin state with ml=1, which has a lifetime of days, whereas the lifetime of the excited spin states in the NV centers is in the region of milliseconds (Laraoui et al., Nature Comm., DOI: 10.1038/ncomms2685). By means of this measure, it is possible in principle to resolve frequency shifts in the nuclear spin resonances to be measured of a few Hz.

[0037] The lower portion of the schematic section view shown shows a reference magnetic 27 which can provide, for example, a magnetic field with a strength of 100 mT. The reference magnet 27 is especially formed by a coil in the spatial proximity of the other components of the analysis device. By means of the magnet 27, the external magnetic field required for excitation of the characteristic spin precession is generated. Compared to standard NMR instruments, the reference magnet 27 can be much smaller, since, by contrast with conventional NMR, it is not necessary to synchronize a collective of identically directed nuclear spins in a relatively large sample volume; instead, individual nuclear spins in a small sample volume have to be read out.

[0038] Through structuring of the diamond layer 25, for example in the form of tubes or needles, it is possible to increase the surface area, by means of which the sensitivity can be increased. By means of capillary structures in the diamond layer 25, the sample can be retained for a longer period of time, which allows the measurement time to be prolonged and hence the measurability to be improved.

[0039] The analysis device 20 further comprises an element 28 for heating and/or cooling. By heating the device on completion of measurement, it is possible, for example, to remove sample residues on the diamond layer 25. If the diamond layer 25 contains capillaries, for example, in order to retain a sample for longer, the sample liquid can be evaporated after the measurement by heating the device by means of the heating element 28. This can be utilized for regeneration of the sensor. Cooling by means of the element 28 can be used in order to re-establish defined measurement conditions after heating. In addition, cooling in the sense of a cold trap can be used in order to condense any gaseous sample.

[0040] Advantageously, a multitude of NV centers or NV sensors to be evaluated individually is present in the diamond layer 25. Correspondingly, the photodiode 23 can also be configured as an arrangement of two or more photodiodes. By means of this measure, the concentration sensitivity for a particular molecular species can be increased further.

[0041] The configuration of an analysis device 20 of the invention shown in FIG. 2 can especially be used as a fuel sensor, for example as a fuel quality sensor. However, the analysis device of the invention is not restricted thereto. The liquid to be analyzed, i.e. the fuel, for example, is conducted over the diamond layer 25 through microfluidic channels 29. It may be preferable here that the liquid flow is interrupted during the measurement; this is achieved by switching an appropriate inlet valve 30. During the measurement, the inlet valve 30 is thus closed, in order to keep the liquid to be analyzed within the region of the sensitive component 25, i.e. of the diamond layer. After the measurement, the valve 30 is opened, such that the liquid to be analyzed in the channels 29 can be exchanged by virtue of a pressure differential between the inlet of the sensor in the region of the inlet valve 30 and between the opposite outlet, indicated here by an arrow 31. The material 32 which is permeated by the channels 29 is appropriately optically transparent, such that the optical excitation radiation from the light source 33 can reach the NV centers in the diamond layer 25 without significant losses.

[0042] FIG. 3 illustrates a further example of an analysis device 40 of the invention, which can be integrated, for example, into a respiratory gas analysis device. In a comparable manner to the configuration illustrated in FIG. 2, the analysis device 40 comprises a carrier substrate 41 into which a photodiode array 43 is integrated. Above the region comprising the photodiode array 43 is an optical filter layer 44. Arranged atop the optical filter layer 44 is a diamond layer 45 with integrated NV centers (sensitive component). In the spatial proximity of the diamond layer 45 is a microwave antenna 46 for introduction of electromagnetic excitation radiation in the microwave range. Arranged atop the carrier substrate 41 is an LED structure 42 (or a VCSEL structure) with a light source for emission of electromagnetic radiation in the optical range. The structure 42 is structured in such a way that the sample to be analyzed can flow through it, indicated here by the arrow 51. Beneath the carrier substrate 41 is an element 48 for cooling and heating of the analysis device 40. This may, for example, be a heatable Peltier element. In the spatial proximity of these structures is a magnet 47 intended to generate the reference magnetic field, in order to induce the spin precession and the magnetic resonances in the NV centers of the diamond layer 45. For the analysis device of the invention, for example, a magnetic field of B=100 mT is sufficient, since the measurement principle used in accordance with the invention via the NV centers in diamond is extremely sensitive. The overall dimensions of such a monolithically integratable NMR sensor structure may, for example, be about 5 cm5 cm. Thus, the analysis device of the invention is very suitable for miniaturized applications. For example, such an analysis device may be incorporated into a handheld respiratory gas analysis device which can be used by a patient as required on an everyday basis.

[0043] Especially in the case of devices which are used for analysis of gaseous samples, for example respiratory gas, condensation of the gaseous sample is appropriately envisaged. In the case of the device 40, the element 48 can be used for this purpose to implement a cold trap. When the gaseous sample is conducted through the channels of the structure 42 (arrow 51), the carrier 41 is cooled together with the sensitive diamond layer 45 arranged thereon, such that the sample condenses directly on the diamond layer 45. The analysis can subsequently be effected in a liquid phase of the sample. On completion of measurement, particularly the region of the diamond layer 45 can be treated by means of the combined heating and cooling element 48, such that the condensate is removed again by evaporation, and the analysis device 40 can be prepared for a new measurement.

[0044] FIG. 4 illustrates the integration of the analysis device 40 from FIG. 3 into a respiratory gas analysis device 60. The respiratory gas analysis device has a mouthpiece 61 through which the exhaled respiratory air from a patient or from a user in general is blown into the device 60. For reasons of hygiene, the mouthpiece may be equipped with a microbial filter. The respiratory gas analysis device 60 further comprises an analysis chamber 62 which contains the analysis device (measurement device) already elucidated with reference to FIG. 3. By means of corresponding conduction of an air flow 63 within the device, the air arrives in the channel structures of the analysis device 40, such that the exhaled respiratory air (respiratory gas) is conducted across the diamond layer 45 of the analysis device 40. In this case, the combined heating and cooling element 48 provides a cold trap, such that the respiratory gas, when it arrives in the region of the diamond layer 45, condenses and can be analyzed in the liquid phase by the principle of the invention.