RESULTS AND PUBLICATIONS
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Hyperpolarised water
Hyperpolarized water
Hyperpolarized water through dissolution dynamic nuclear polarization with UV-generated radicals
Pinon AC, Capozzi A, Ardenkjaer-Larsen JH
DTU partner
Communications Chemistry, 2020
In recent years, hyperpolarization of water protons via dissolution Dynamic Nuclear Polarization (dDNP) has attracted increasing interest in the magnetic resonance community. Hyperpolarized water may provide an alternative to Gd-based contrast agents for angiographic and perfusion Magnetic Resonance Imaging (MRI) examinations, and it may report on chemical and biochemical reactions and proton exchange while perfoming Nuclear Magnetic Resonance (NMR) investigations. However, hyperpolarizing water protons is challenging. The main reason is the presence of radicals, required to create the hyperpolarized nuclear spin state. Indeed, the radicals will also be the main source of relaxation during the dissolution and transfer to the NMR or MRI system. In this work, we report water magnetizations otherwise requiring a field of 10,000 T at room temperature on a sample of pure water, by employing dDNP via UV-generated, labile radicals. We demonstrate the potential of our methodology by acquiring a 15N spectrum from natural abundance urea with a single scan, after spontaneous magnetization transfer from water protons to nitrogen nuclei.
dDNP hyperpolarised nitrogen-15 and animals models
Increasing the sensitivity of hyperpolarized [15N2]urea detection by serial transfer of polarization to spin-coupled protons
Kreis F, Wright AJ, Somai V, Katz-Brull R, Brindle KM
HMO and UCAM partners
Magnetic Resonance in Medicine, 2020
Purpose: Hyperpolarized 15N-labeled molecules have been proposed as imaging agents for investigating tissue perfusion and pH. However, the sensitivity of direct 15N detection is limited by the isotope's low gyromagnetic ratio. Sensitivity can be increased by transferring 15N hyperpolarization to spin-coupled protons provided that there is not significant polarization loss during transfer. However, complete polarization transfer would limit the temporal window for imaging to the order of the proton T1 (2-3 s). To exploit the long T1 offered by storing polarization in 15N and the higher sensitivity of 1 H detection, we have developed a pulse sequence for partial polarization transfer. Methods: A polarization transfer pulse sequence was modified to allow partial polarization transfer, as is required for dynamic measurements, and that can be implemented with inhomogeneous B1 fields, as is often the case in vivo. The sequence was demonstrated with dynamic spectroscopy and imaging measurements with [ 15N2]urea. Results: When compared to direct 15N detection, the sequence increased the signalto-noise ratio (SNR) by a factor of 1.72 ± 0.25, where both experiments depleted ~20% of the hyperpolarization (>10-fold when 100% of the hyperpolarization is used). Simulations with measured cross relaxation rates showed that this sequence gave up to a 50-fold increase in urea proton polarization when compared to spontaneous polarization transfer via cross relaxation. Conclusion: The sequence gave an SNR increase that was close to the theoretical limit and can give a significant SNR benefit when compared to direct 13C detection of hyperpolarized [13C]urea
Directly Bound Deuterons Increase X-Nuclei Hyperpolarization using Dynamic Nuclear Polarization
Rooney CHE, Galiel A, Shaul D, Tyler DJ, Grist JT, Katz-Brull R
UOXF and HMO partners
ChemPhysChem, 2023
Deuterated 13C sites in sugars (D-glucose and 2-deoxy-D-glucose) showed 6.3-to-17.5-fold higher solid-state dynamic nuclear polarization (DNP) levels than their respective protonated sites at 3.35T. This effect was found to be unrelated to the protonation of the bath. Deuterated 15N in sites bound to exchangeable protons ([15N2]urea) showed a 1.3-fold higher polarization than their respective protonated sites at the same magnetic field. This relatively smaller effect was attributed to incomplete deuteration of the 15N sites due to the solvent mixture. For a 15N site that is not bound to protons or deuterons ([15N]nitrate), deuteration of the bath did not affect the polarization level. These findings suggest a phenomenon related to DNP of X-nuclei directly bound to deuteron(s) as opposed to proton(s). It appears that direct binding to deuterons increases the solid-state DNP polarization level of X-nuclei which are otherwise bound to protons.
Real-time influence of intracellular acidification and Na+/H+ exchanger inhibition on in-cell pyruvate metabolism in the perfused mouse heart: A 31P-NMR and hyperpolarized 13C-NMR study
Shaul D, Lev-Cohain N, Sapir G, Sosna J, Gomori JM, Joskowicz L, Katz-Brull R
HMO partner
NMR in Biomedicine, 2023
Disruption of acid–base balance is linked to various diseases and conditions. In the heart, intracellular acidification is associated with heart failure, maladaptive cardiac hypertrophy, and myocardial ischemia. Previously, we have reported that the ratio of the in-cell lactate dehydrogenase (LDH) to pyruvate dehydrogenase (PDH) activities is correlated with cardiac pH. To further characterize the basis for this correlation, these in-cell activities were investigated under induced intracellular acidification without and with Na+/H+ exchanger (NHE1) inhibition by zoniporide. Male mouse hearts (n = 30) were isolated and perfused retrogradely. Intracellular acidification was performed in two ways: (1) with the NH4Cl prepulse methodology; and (2) by combining the NH4Cl prepulse with zoniporide. 31P NMR spectroscopy was used to determine the intracellular cardiac pH and to quantify the adenosine triphosphate and phosphocreatine content. Hyperpolarized [1-13C]pyruvate was obtained using dissolution dynamic nuclear polarization. 13C NMR spectroscopy was used to monitor hyperpolarized [1-13C]pyruvate metabolism and determine enzyme activities in real time at a temporal resolution of a few seconds using the product-selective saturating excitation approach. The intracellular acidification induced by the NH4Cl prepulse led to reduced LDH and PDH activities (−16% and −39%, respectively). This finding is in line with previous evidence of reduced myocardial contraction and therefore reduced metabolic activity upon intracellular acidification. Concomitantly, the LDH/PDH activity ratio increased with the reduction in pH, as previously reported. Combining the NH4Cl prepulse with zoniporide led to a greater reduction in LDH activity (−29%) and to increased PDH activity (+40%). These changes resulted in a surprising decrease in the LDH/PDH ratio, as opposed to previous predictions. Zoniporide alone (without intracellular acidification) did not change these enzyme activities. A possible explanation for the enzymatic changes observed during the combination of the NH4Cl prepulse and NHE1 inhibition may be related to mitochondrial NHE1 inhibition, which likely negates the mitochondrial matrix acidification. This effect, combined with the increased acidity in the cytosol, would result in an enhanced H+ gradient across the mitochondrial membrane and a temporarily higher pyruvate transport into the mitochondria, thereby increasing the PDH activity at the expense of the cytosolic LDH activity. These findings demonstrate the complexity of in-cell cardiac metabolism and its dependence on intracellular acidification. This study demonstrates the capabilities and limitations of hyperpolarized [1-13C]pyruvate in the characterization of intracellular acidification as regards cardiac pathologies.
Signal enhancement of hyperpolarized 15N sites in solution—increase in solid-state polarization at 3.35 T and prolongation of relaxation in deuterated water mixtures
Gamliel A, Shaul D, Gomori JM, and Katz-Brull R.
HMO partners
NMR in Biomedicine, 2022
Purpose: Hyperpolarized 15N-labeled molecules have been proposed as imaging agents for investigating tissue perfusion and pH. However, the sensitivity of direct 15N detection is limited by the isotope's low gyromagnetic ratio. Sensitivity can be increased by transferring 15N hyperpolarization to spin-coupled protons provided that there is not significant polarization loss during transfer. However, complete polarization transfer would limit the temporal window for imaging to the order of the proton T1 (2-3 s). To exploit the long T1 offered by storing polarization in 15N and the higher sensitivity of 1 H detection, we have developed a pulse sequence for partial polarization transfer. Methods: A polarization transfer pulse sequence was modified to allow partial polarization transfer, as is required for dynamic measurements, and that can be implemented with inhomogeneous B1 fields, as is often the case in vivo. The sequence was demonstrated with dynamic spectroscopy and imaging measurements with [ 15N2]urea. Results: When compared to direct 15N detection, the sequence increased the signalto-noise ratio (SNR) by a factor of 1.72 ± 0.25, where both experiments depleted ~20% of the hyperpolarization (>10-fold when 100% of the hyperpolarization is used). Simulations with measured cross relaxation rates showed that this sequence gave up to a 50-fold increase in urea proton polarization when compared to spontaneous polarization transfer via cross relaxation. Conclusion: The sequence gave an SNR increase that was close to the theoretical limit and can give a significant SNR benefit when compared to direct 13C detection of hyperpolarized [13C]urea
Tolerance of Rodents to an Intravenous Bolus Injection of Sodium Nitrate in a High Concentration
Nitrate, the inorganic anion NO3−, is found in many foods and is an endogenous mammalian metabolite, which is supplied mostly through the diet. Although much is known about the safety of sodium nitrate when given per os, methodological safety data on intravenous bolus injection of sodium nitrate to rodents are lacking. Recently, we have proposed a new use for nitrate, as a contrast agent for magnetic resonance imaging that will be metal free and leave no traces in the body and the environment further to the imaging examination. It was shown that a stable isotope-labelled analog of this ion (15NO3−), in a sodium nitrate solution form and hyperpolarized state, produces a high magnetic resonance signal with prolonged visibility. Therefore, sodium nitrate was targeted for further preclinical development in this context. In the absence of methodological safety data on the potential effects of a high concentration sodium nitrate bolus intravenous injection into rodents, we carried out such an investigation in mice and rats (n = 12 of each, 6 males and 6 females in each group, altogether 24 animals). We show here that an intravenous bolus administration of sodium nitrate at a concentration of 150 mM and a dose of 51 mg/Kg does not lead to adverse effects in mice and rats. This is the first investigation of the tolerance of rodents to an intravenous injection of sodium nitrate.
Accumulation of 3-aminopropylphosphonate in the ex vivo brain observed by phosphorus-31 nuclear magnetic resonance
Shaul D, Grieb B,, Lev-Cohain N, Sosna J, Gomori JM, Katz-Brull R
HMO partner
NMR in Biomedicine, 2022
3-aminopropylphosphonate (3-APP) is known for its use as an exogenous indicator of extracellular volume and pH in phosphorus-31 nuclear magnetic resonance (31P NMR) studies. We used 3-APP for estimating the extracellular volume in NMR studies of several ex vivo preparations including retrograde perfused mouse heart (n = 4), mouse liver slices (n = 2), xenograft breast cancer tumors (n = 7, MCF7), and rat brain slices (n = 4). In the former three preparations, the 3-APP signal was stable in lineshape and intensity for hours and the chemical shift of the signal in the presence of the biological sample was the same as in the perfusion medium without the biological sample. However, in studies of brain slices, the 3-APP signal appeared split into two, with an upfield component (0.7 ± 0.1 ppm to the left) increasing with time and showing a wider linewidth (66.7 ± 12.6 vs. 39.1 ± 7.6 Hz, the latter is of the perfusion medium signal). This finding suggests that 3-APP inadvertently accumulated in brain slices, most likely as a membrane bound form. This observation limits the use of 3-APP as an inert biochemical indicator in brain preparations and should be taken into account when using 3-APP in vivo.
Genetic algorithm-based optimization of NMR pulse sequences
Somai V, Kreis F, Tsyben A, Cia ML, Hesse F, Wright AJ, Brindle KM
UCAM partner
Magnetic Resonance in Medicine, 2021
Purpose: The performance of pulse sequences in vivo can be limited by fast relaxation rates, magnetic field inhomogeneity, and nonuniform spin excitation. We describe here a method for pulse sequence optimization that uses a stochastic numerical solver that in principle is capable of finding a global optimum. The method provides a simple framework for incorporating any constraint and implementing arbitrarily complex cost functions. Efficient methods for simulating spin dynamics and incorporating frequency selectivity are also described. Methods: Optimized pulse sequencesfor polarization transfer between protons and X-nuclei and excitation pulsesthat eliminate J-coupling modulation were evaluated experimentally using a surface coil on phantoms, and also the detection of hyperpolarized [2-13C]lactate in vivo in the case of J-coupling modulation-free excitation. Results: The optimized polarization transfer pulses improved the SNR by ~50% with a more than twofold reduction in the B1 field, and J-coupling modulationfree excitation was achieved with a more than threefold reduction in pulse length. Conclusion: This process could be used to optimize any pulse when there is a need to improve the uniformity and frequency selectivity of excitation as well as to design new pulses to steer the spin system to any desired achievable state.
Assessing the effect of anesthetic gas mixtures on hyperpolarized 13C pyruvate metabolism in the rat brain
Healicon R, Rooney CHE, Ball V, Shinozaki A, Miller JJ, Smart S, Radford-Smith D, Anthony D, Tyler DJ, Grist JT
UOXF partner
Magnetic Resonance in Medicine, 2022
To determine the effect of altering anesthetic oxygen protocols on measurements of cerebral perfusion and metabolism in the rodent brain. Methods Seven rats were anesthetized and underwent serial MRI scans with hyperpolarized [1–13C]pyruvate and perfusion weighted imaging. The anesthetic carrier gas protocol used varied from 100:0% to 90:10% to 60:40% O2:N2O. Spectra were quantified with AMARES and perfusion imaging was processed using model-free deconvolution. A 1-way ANOVA was used to compare results across groups, with pairwise t tests performed with correction for multiple comparisons. Spearman's correlation analysis was performed between O2% and MR measurements. Results There was a significant increase in bicarbonate:total 13C carbon and bicarbonate:13C pyruvate when moving between 100:0 to 90:10 and 100:0 to 60:40 O2:N2O % (0.02 ± 0.01 vs. 0.019 ± 0.005 and 0.02 ± 0.01 vs. 0.05 ± 0.02, respectively) and (0.04 ± 0.01 vs. 0.03 ± 0.01 and 0.04 ± 0.01 vs. 0.08 ± 0.02, respectively). There was a significant difference in 13C pyruvate time to peak when moving between 100:0 to 90:10 and 100:0 to 60:40 O2:N2O % (13 ± 2 vs. 10 ± 1 and 13 ± 2 vs. 7.5 ± 0.5 s, respectively) as well as significant differences in cerebral blood flow (CBF) between gas protocols. Significant correlations between bicarbonate:13C pyruvate and gas protocol (ρ = −0.47), mean transit time and gas protocol (ρ = 0.41) and 13C pyruvate time-to-peak and cerebral blood flow (ρ = −0.54) were also observed. Conclusions These results demonstrate that the detection and quantification of cerebral metabolism and perfusion is dependent on the oxygen protocol used in the anesthetized rodent brain.
Developing a metabolic clearance rate framework as a translational analysis approach for hyperpolarized 13C magnetic resonance imaging
Grist JT, Bogh N, Sovso Hansen E, Schneider AM, Healicon R, Ball V, Milller JJJ, Smart S, Couch Y, Buchan AM, Tyler DJ, Laustsen C
UOXF partner
Scientific Reports, 2023
Hyperpolarized carbon-13 magnetic resonance imaging is a promising technique for in vivo metabolic interrogation of alterations between health and disease. This study introduces a formalism for quantifying the metabolic information in hyperpolarized imaging. This study investigated a novel perfusion formalism and metabolic clearance rate (MCR) model in pre-clinical stroke and in the healthy human brain. Simulations showed that the proposed model was robust to perturbations in T1, transmit B1, and kPL. A significant difference in ipsilateral vs contralateral pyruvate derived cerebral blood flow (CBF) was detected in rats (140 ± 2 vs 89 ± 6 mL/100 g/min, p < 0.01, respectively) and pigs (139 ± 12 vs 95 ± 5 mL/100 g/min, p = 0.04, respectively), along with an increase in fractional metabolism (26 ± 5 vs 4 ± 2%, p
PHIP-SAH
Instrumentation for Hydrogenative Parahydrogen-Based Hyperpolarization Techniques
Schmidt AB, Bowers RC, Buckenmaier K, Chekmenev EY, de Maissin H, Eills J, Ellermann F, Gl:oggler S, Gordon JW, Knecht S, Koptyug IV, Kuhn J, Pravdivtsev AN, Reineri F, Theis T, Them K, Hövener JB
UNITO partner
PNAS, 2021
The unique properties of the entangled, antisymmetric nuclear spin state of dihydrogen, parahydrogen (pH2), has intrigued physicists, chemists, and other scientists for almost a century. pH2 was used as a model system in the early days of quantum mechanics1 and is used for fueling rockets as well as combustion-free cars today. In the 1980s, pH2 was discovered as a convenient and potent source of spin order, allowing the enhancement of the signals of magnetic resonance (MR) by several orders of magnitude…..Here, we review the different instrumentations for pH2 hyperpolarization, with an emphasis on biomedical applications. To keep this review concise, we focus on setups for hydrogenative pH2-based hyperpolarization alone and the most recent literature (∼last 5 years); still, we refer to pioneering and game-changing developments whenever appropriate and when other methods (SABRE, DNP, SEOP, etc.) show similar instrumentational aspects. Dedicated reviews on SABRE related instrumentation, spin-order transfer, and pH2 production are expected to be published elsewhere.
Hydrogenative-PHIP polarized metabolites for biological studies
Reinferi F, Cavallari E, Carrera C, Aime S
UNITO partner
Magnetic Resonance Materials in Physics, Biology and Medicine
ParaHydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, but its application to biological investigations has been hampered, so far, due to chemical challenges. PHIP is obtained by means of the addition of hydrogen, enriched in the para-spin isomer, to an unsaturated substrate. Both hydrogen atoms must be transferred to the same substrate, in a pairwise manner, by a suitable hydrogenation catalyst; therefore, a de-hydrogenated precursor of the target molecule is necessary. This has strongly limited the number of parahydrogen polarized substrates. The non-hydrogenative approach brilliantly circumvents this central issue, but has not been translated to in-vivo yet. Recent advancements in hydrogenative PHIP (h-PHIP) considerably widened the possibility to hyperpolarize metabolites and, in this review, we will focus on substrates that have been obtained by means of this method and used in vivo. Attention will also be paid to the requirements that must be met and on the issues that have still to be tackled to obtain further improvements and to push PHIP substrates in biological applications.
Metabolic Reactions Studied by Zero- and Low-Field Nuclear Magnetic Resonance
Eills J, Picazo-Frutos R, Bondar O, Cavallari E, Carrera C, Barker SJ, Utz M, Aime S, Reiner F, Budker D, Blanchard JW
UNITO partner
arXiv, 2022
State-of-the-art magnetic resonance imaging uses hyperpolarized molecules to track metabolism in vivo, but large superconducting magnets are required, and the strong magnetic fields largely preclude measurement in the presence of conductive materials and magnify problems of magnetic susceptibility inhomogeneity. Operating at zero and low field circumvents these limitations, but until now has not been possible due to limited sensitivity. We show that zero- and low-field nuclear magnetic resonance can be used for probing two important metabolic reactions: the conversion of hyperpolarized fumarate to malate and pyruvate to lactate. This work paves the way to a heretofore unexplored class of biomedical imaging applications.
Rapid Hyperpolarization and Purification of the Metabolite Fumarate in Aqueous Solution
Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at 13C polarization levels of 30–45%.
ParaHydrogen Polarized Ethyl-[1-13C]pyruvate in Water, a Key Substrate for Fostering the PHIP-SAH Approach to Metabolic Imaging
Carrera C, Cavallari E, Digilio G, Bondar O, Aime S, Reineri F
UNITO partner
ChemPhysChem 2021
An efficient synthesis of vinyl-[1-13C]pyruvate has been reported, from which 13C hyperpolarized (HP) ethyl-[1-13C]pyruvate has been obtained by means of ParaHydrogen Induced Polarization (PHIP). Due to the intrinsic lability of pyruvate, which leads quickly to degradation of the reaction mixture even under mild reaction conditions, the vinyl-ester has been synthesized through the intermediacy of a more stable ketal derivative. 13C and 1H hyperpolarizations of ethyl-[1-13C]pyruvate, hydrogenated using ParaHydrogen, have been compared to those observed on the more widely used allyl-derivative. It has been demonstrated that the spin order transfer from ParaHydrogen protons to 13C, is more efficient on the ethyl than on the allyl-esterdue to the larger J-couplings involved. The main requirements needed for the biological application of this HP product have been met, i. e. an aqueous solution of the product at high concentration (40 mM) with a good 13C polarization level (4.8 %) has been obtained. The in vitro metabolic transformation of the HP ethyl-[1-13C]pyruvate, catalyzed by an esterase, has been observed. This substrate appears to be a good candidate for in vivo metabolic investigations using PHIP hyperpolarized probes.
Effect of the hydrogenation solvent in the PHIP-SAH hyperpolarization of [1-13C]pyruvate
Bondar O, Cavallaari E, Carrera C, Aime S, Reineri F
UNITO partner
Catalysis Today 2022
ParaHydrogen Induced Polarization-Side Arm Hydrogenation (PHIP-SAH) is an inexpensive tool to obtain hyperpolarized pyruvate (and other metabolites) that can be applied to in vivo diagnostics, for the investigation of metabolic processes. This method is based on hydrogenation, using hydrogen enriched in the para-isomer, of unsaturated substrates, catalyzed, usually, by a homogeneous rhodium(I) complex. In this work, the effect of the solvent on the hydrogenation efficiency and the hyperpolarization level were investigated. Coordinating solvents, such as acetone and methanol, can increase significantly either the efficiency or the hyperpolarization level, but they are not compatible with the intended metabolic applications. The phase extraction of the hyperpolarized product (sodium pyruvate) in an aqueous solution was obtained carrying out the hydrogenation reaction in chloroform and toluene. The traces of the organic solvents in the water phase were removed, by means of filtration through a lipophilic resin, thus improving the biocompatibility of the aqueous solution of the hyperpolarized product.
Design and Testing of Diagnostic MRI/MRS Applications Based On Signal Enhancement by Parahydrogen-Induced Polarization
Parahydrogen-induced polarization is a hyperpolarization method that exploits the spin order of hydrogen enriched in the para-isomer, by means of a chemical reaction. Recently, its field of application has been extended significantly, through the introduction of non-hydrogenative PHIP (i. e. SABRE) and of innovative h-PHIP strategies that allowed to increase the intensity of the MR signals in molecules relevant for biological applications. This Concept article aims to show the potentialities of this hyperpolarization method in the field of diagnostics, through the discussion of some of the reported applications of parahydrogen polarized substrates. A section is also dedicated to the methods that have been introduced for the purification of parahydrogen polarized products, in order to make them suitable for biological studies.
Nanodiamond polarisation
Long-lived ensembles of shallow NV- centers in flat and nanostructured diamond by photoconversion
Shallow, negatively charged nitrogen-vacancy centers (NV−) in diamond have been proposed for high-sensitivity magnetometry and spin-polarization transfer applications. However, surface effects tend to favor and stabilize the less useful neutral form, the NV0 centers. Here, we report the effects of green laser irradiation on ensembles of nanometer-shallow NV centers in flat and nanostructured diamond surfaces as a function of laser power in a range not previously explored (up to 150 mW/μm2 ). Fluorescence spectroscopy, optically detected magnetic resonance (ODMR), and charge-photoconversion detection are applied to characterize the properties and dynamics of NV− and NV0 centers. We demonstrate that high laser power strongly promotes photoconversion of NV0 to NV− centers. Surprisingly, the excess NV− population is stable over a timescale of 100 ms after switching off the laser, resulting in long-lived enrichment of shallow NV−. The beneficial effect of photoconversion is less marked in nanostructured samples. Our results are important to inform the design of samples and experimental procedures for applications relying on ensembles of shallow NV− centers in diamond.
Divergent effects of laser irradiation on ensembles of nitrogen-vacancy centers in bulk and nano-diamonds: implications for biosensing
Ensembles of negatively charged nitrogen vacancy centers (NV-) in diamond have been proposed for sensing of magnetic fields and paramagnetic agents, and as a source of spin-order for the hyperpolarization of nuclei in magnetic resonance applications. To this end, strongly fluorescent nanodiamonds represent promising materials, with large surface areas and dense ensembles of NV-. However, surface effects tend to favor the less useful neutral form, the NV0 centers. Here, we study the fluorescence properties and optically detected magnetic resonance (ODMR) of NV- centers as a function of laser power in strongly fluorescent bulk diamond and in nanodiamonds obtained by nanomilling the native material. In bulk diamond, we find that increasing laser power increases ODMR contrast, consistent with a power-dependent increase in spin-polarization. Surprisingly, in nanodiamonds we observe a non-monotonic behavior, with a decrease in ODMR contrast at higher laser power that can be ascribed to more efficient NV- -> NV0 photoconversion in nanodiamonds compared to bulk diamond, resulting in depletion of the NV- pool. We also studied this phenomenon in cell cultures following internalization of NDs in macrophages. Our findings show that surface effects in nanodiamonds substantially affect the NV properties and provide indications for the adjustment of experimental parameters.
Photoconversion of shallow nitrogen-vacancy centers in flat and nanostructured diamond under high-power laser irradiation
Shallow, negatively-charged Nitrogen-Vacancy centers (NV- ) in diamond have been proposed for high-sensitivity magnetometry and spinpolarization transfer applications. However, surface effects tend to favor and stabilize the less useful neutral form, the NV0 centers. Here, we report the effects of green laser irradiation on ensembles of nanometer-shallow NV centers in flat and nanostructured diamond surfaces as a function of laser power in a range not previously explored (up to 150 mW/μm 2 ). Raman spectroscopy, opticallydetected-magnetic-resonance (ODMR) and charge-photoconversion fluorescence detection are applied to characterize the properties and dynamics of NV- and NV0 centers. We demonstrate that high laser power strongly promotes photoconversion of NV0 to NV- centers. Surprisingly, the excess NV- population is stable over a time scale of one hundred milliseconds after switching off the laser, resulting in long-lived enrichment of shallow NV- . The beneficial effect of photoconversion is less marked in nanostructured samples. Our results are important to inform the design of samples and experimental procedures for applications relying on ensembles of shallow NV- centers in diamond.
Advances in Stabilization and Enrichment of Shallow Nitrogen-Vacancy Centers in Diamond for Biosensing and Spin-Polarization Transfer
Negatively charged nitrogen-vacancy (NV−) centers in diamond have unique magnetooptical properties, such as high fluorescence, single-photon generation, millisecond-long coherence times, and the ability to initialize and read the spin state using purely optical means. This makes NV− centers a powerful sensing tool for a range of applications, including magnetometry, electrometry, and thermometry. Biocompatible NV-rich nanodiamonds find application in cellular microscopy, nanoscopy, and in vivo imaging. NV− centers can also detect electron spins, paramagnetic agents, and nuclear spins. Techniques have been developed to hyperpolarize 14N, 15N , and 13C nuclear spins, which could open up new perspectives in NMR and MRI. However, defects on the diamond surface, such as hydrogen, vacancies, and trapping states, can reduce the stability of NV− in favor of the neutral form (NV0 ), which lacks the same properties. Laser irradiation can also lead to charge-state switching and a reduction in the number of NV− centers. Efforts have been made to improve stability through diamond substrate doping, proper annealing and surface termination, laser irradiation, and electric or electrochemical tuning of the surface potential. This article discusses advances in the stabilization and enrichment of shallow NV− ensembles, describing strategies for improving the quality of diamond devices for sensing and spin-polarization transfer applications. Selected applications in the field of biosensing are discussed in more depth.
Nanodiamonds – synthesis, production and coating
Laser-Synthesis of NV-Centers-Enriched Nanodiamonds: Effect of Different Nitrogen Sources
Due to the large number of possible applications in quantum technology fields—especially regarding quantum sensing—of nitrogen-vacancy (NV) centers in nanodiamonds (NDs), research on a cheap, scalable and effective NDs synthesis technique has acquired an increasing interest. Standard production methods, such as detonation and grinding, require multistep post-synthesis processes and do not allow precise control in the size and fluorescence intensity of NDs. For this reason, a different approach consisting of pulsed laser ablation of carbon precursors has recently been proposed. In this work, we demonstrate the synthesis of NV-fluorescent NDs through pulsed laser ablation of an N-doped graphite target. The obtained NDs are fully characterized in the morphological and optical properties, in particular with optically detected magnetic resonance spectroscopy to unequivocally prove the NV origin of the NDs photoluminescence. Moreover, to compare the different fluorescent NDs laser-ablation-based synthesis techniques recently developed, we report an analysis of the effect of the medium in which laser ablation of graphite is performed. Along with it, thermodynamic aspects of the physical processes occurring during laser irradiation are analyzed. Finally, we show that the use of properly N-doped graphite as a target for laser ablation can lead to precise control in the number of NV centers in the produced NDs.
Mechanistic insights of seeded diamond growth from molecular precursors
We report mechanistic insights of the bottom-up synthesis of nanodiamonds (NDs) from adamantane derivatives as molecular precursors. Thermal cracking of tetracosane below the decomposition temperature of adamantane, 1-adamantylamine or 2-azaadamantane revealed the initial steps of seeded diamond growth mechanism based on pyrolysis studies.
Germanium iodide mediated synthesis of nanodiamonds from adamantane “seeds” under moderate high-pressure high-temperature conditions
There is an emerging demand for nanodiamonds with controlled structures or shapes for applications in biomedical imaging and sensing. Synthetic conditions proceeding at less harsh temperatures and pressures are considered crucial to control nanodiamond formation process. We report a germanium iodide (GeI4) mediated synthesis of nanodiamonds from diamondoid molecules and alkane hydrocarbon under moderate high-pressure high-temperature (m-HPHT) conditions. For the first time, GeI4 is used to generate nanodiamonds at 3.5 GPa and 500 °C, which is considerably lower than the conditions reported for common HPHT methods for nanodiamond synthesis. The strategy reported herein allows synthesizing nanodiamonds based on well-defined molecular precursors, which paves the way to a bottom-up diamond synthesis designed at a molecular level.
Nanodiamond Theranostic for Light-Controlled Intracellular Heating and Nanoscale Temperature Sensing
Temperature is an essential parameter in all biological systems, but information about the actual temperature in living cells is limited. Especially, in photothermal therapy, local intracellular temperature changes induce cell death but the local temperature gradients are not known. Highly sensitive nanothermometers would be required to measure and report local temperature changes independent of the intracellular environment, including pH or ions. Fluorescent nanodiamonds (ND) enable temperature sensing at the nanoscale independent of external conditions. Herein, we prepare ND nanothermometers coated with a nanogel shell and the photothermal agent indocyanine green serves as a heat generator and sensor. Upon irradiation, programmed cell death was induced in cancer cells with high spatial control. In parallel, the increase in local temperature was recorded by the ND nanothermometers. This approach represents a great step forward to record local temperature changes in different cellular environments inside cells and correlate these with thermal biology.
Fluorescent Nanodiamond–Nanogels for Nanoscale Sensing and Photodynamic Applications
Fluorescent nanodiamonds (NDs) are carbon-based nanoparticles with various outstanding magneto optical properties. After preparation, NDs have a variety of different surface groups that determine their physicochemical properties. For biological applications, surface modifications are crucial to impart a new interface for controlled interactions with biomolecules or cells. Herein, a straightforward synthesis concept denoted “adsorption crosslinking” is applied for the efficient modification of NDs, which sequentially combines fast noncovalent adsorption based on electrostatic interactions and subsequent covalent crosslinking. As a result, a very thin and uniform nanogel (NG) coating surrounding the NDs is obtained, which imparts reactive groups as well as high colloidal stability. The impact of the reaction time, monomer concentration, molecular weight, structure of the crosslinker on the resulting NG shell, the availability of reactive chemical surface functions, and the quantum sensing properties of the coated NDs are assessed and optimized. Postmodification of the NG-coated NDs is achieved with phototoxic ruthenium complexes yielding ND-based probes suitable for photodynamic applications. The adsorption crosslinking ND functionalization reported herein provides new avenues toward functional probes and traceable nanocarriers for high-resolution bioimaging, nanoscale sensing, and photodynamic applications.
High Pressure Induced Formation of Carbon Nanorods from Tetracosane
Morphology control of carbon nanostructures is essential for improving their performance in many applications. Direct pyrolysis of organic precursors, however, usually yields bulk amorphous carbon. Therefore, traditional methods for controlling the morphology of carbon nanostructures involve multistep processes and complex precursor molecules. While various methods have been developed under ambient pressure, the impact of pressure on the morphology of the resulting carbon nanostructures remains unexplored. Herein, we present the synthesis of carbon nanorods by direct pyrolysis of the low-cost aliphatic hydrocarbon tetracosane under high pressure conditions. The diameters of the carbon nanorods are adjusted by simply varying the 2 synthetic pressures. High pressure allows controlling both the nanorod morphology as well as the degree of order, and local conductivity of the thus prepared nanorods has been confirmed by conductive AFM measurements. Our method promises a convenient strategy to synthesize carbon nanostructures with controlled morphology and high ordered chemical structure, which opens opportunities for potential electronic and electrochemical applications.
Magnetic resonance acquisition technology for hyperpolarised multinuclear MRI
Design and Analysis of Field-of-View independent k-space Trajectories for Magnetic Resonance Imaging
This manuscript describes a method of three-dimensional k-space sampling that is based on a generalised form of the previously introduced “Seiffert Spirals,” which exploits the equality between undersampling and the reconstruction of a field of view which is larger than what is represented by the primary sampling density, leading to an imaging approach that does not require any prior commitment to an imaging field of view. The concept of reconstructing arbitrary FOVs based on a low-coherently sampled k-space is demonstrated analytically by simulations of the corresponding point spread functions and by an analysis of the noise power spectrum of undersampled datasets. In-vivo images highlight the feasibility of the presented approach by reconstructing white noise governed images from an undersampled datasets with a smaller encoded FOV. Beneficial properties are especially given by an artefact behaviour, which is widely comparable to the introduction of white noise in the image domain. Furthermore, these aliasing properties provide a promising precondition for the combination with non-linear reconstruction techniques such as Compressed Sensing. All presented results show dominant lowcoherent aliasing properties, leading to a noise-like aliasing behaviour, which enables parameterization of the imaging sequence according to a given resolution and scan-time, without the need for FOV considerations.
RF Coil Design for Accurate Parallel Imaging on 13C MRSI using 23Na Sensitivity Profiles
Purpose: To develop a coil-based method to obtain accurate sensitivity profiles in 13C MRI at 3T from the endogenous 23Na. An eight-channel array is designed for 13C MR acquisitions. As application examples, the array is used for two-fold accelerated acquisitions of both hyperpolarized 13C metabolic imaging of pig kidneys and the human brain. Methods: A flexible coil array was tuned optimally for 13C at 3T (32.1 MHz), with the coil coupling coefficients matched to be nearly identical at the resonance frequency of 23Na (33.8 MHz). This is done by enforcing a high decoupling (obtained through highly mismatched preamplifiers) and adjusting the coupling frequency response. The SNR performance is compared to reference coils. Results: The measured sensitivity profiles on a phantom showed high spatial similarity for 13C and 23Na resonances, with average noise correlation of 9 and 11%, respectively. For acceleration factors 2, 3, and 4, the obtained maximum g-factors were 1.0, 1.1, and 2.6, respectively. The 23Na profiles obtained in vivo could be used successfully to perform two-fold acceleration of hyperpolarized 13C 3D acquisitions of both pig kidneys and a healthy human brain. Conclusion: A receive array has been developed in such a way that the 13C sensitivity profiles could be accurately obtained from measurements at the 23Na frequency. This technique facilitates accelerated acquisitions for hyperpolarized 13C imaging. The SNR performance obtained at the 13C frequency, compares well to other state-of-the-art coils for the same purpose, showing slightly better superficial and central SNR.
Reviews - hyperpolarisation
Hyperpolarized 13C magnetic resonance imaging for noninvasive assessment of tissue inflammation
Inflammation is a central mechanism underlying numerous diseases and incorporates multiple known and potential future therapeutic targets. However, progress in developing novel immunomodulatory therapies has been slowed by a need for improvement in noninvasive biomarkers to accurately monitor the initiation, development and resolution of immune responses as well as their response to therapies. Hyperpolarized magnetic resonance imaging (MRI) is an emerging molecular imaging technique with the potential to assess immune cell responses by exploiting characteristic metabolic reprogramming in activated immune cells to support their function. Using specific metabolic tracers, hyperpolarized MRI can be used to produce detailed images of tissues producing lactate, a key metabolic signature in activated immune cells. This method has the potential to further our understanding of inflammatory processes across different diseases in human subjects as well as in preclinical models. This review discusses the application of hyperpolarized MRI to the imaging of inflammation, as well as the progress made towards the clinical translation of this emerging technique.
Hyperpolarized Carbon-13 MRI in Breast Cancer
One of the hallmarks of cancer is metabolic reprogramming, including high levels of aerobic glycolysis (the Warburg effect). Pyruvate is a product of glucose metabolism, and 13C-MR imaging of the metabolism of hyperpolarized (HP) [1-13C]pyruvate (HP 13C-MRI) has been shown to be a potentially versatile tool for the clinical evaluation of tumor metabolism. Hyperpolarization of the 13C nuclear spin can increase the sensitivity of detection by 4–5 orders of magnitude. Therefore, following intravenous injection, the location of hyperpolarized 13C-labeled pyruvate in the body and its subsequent metabolism can be tracked using 13C-MRI. Hyperpolarized [13C]urea and [1,4-13C2 ]fumarate are also likely to translate to the clinic in the near future as tools for imaging tissue perfusion and post-treatment tumor cell death, respectively. For clinical breast imaging, HP 13C-MRI can be combined with 1H-MRI to address the need for detailed anatomical imaging combined with improved functional tumor phenotyping and very early identification of patients not responding to standard and novel neoadjuvant treatments. If the technical complexity of the hyperpolarization process and the relatively high associated costs can be reduced, then hyperpolarized 13C-MRI has the potential to become more widely available for large-scale clinical trials.
Deuterium Metabolic Imaging
Metabolic imaging with deuterium labeled substrates
Deuterium metabolic imaging (DMI) is an emerging clinically-applicable technique for the non-invasive investigation of tissue metabolism. The generally short T1 values of 2 H-labeled metabolites in vivo can compensate for the relatively low sensitivity of detection by allowing rapid signal acquisition in the absence of significant signal saturation. Studies with deuterated substrates, including [6,60 - 2 H2]glucose, [ 2 H3]acetate, [2 H9]choline and [2,3-2 H2]fumarate have demonstrated the considerable potential of DMI for imaging tissue metabolism and cell death in vivo. The technique is evaluated here in comparison with established metabolic imaging techniques, including PET measurements of 2-deoxy-2-[18F]fluoro-Dglucose (FDG) uptake and 13C MR imaging of the metabolism of hyperpolarized 13C-labeled substrates.