Low Power Microwave Irradiation Research Articles

Microwave-enhanced antibacterial activity of polydopamine-silver hybrid nanoparticles.

The ever-increasing risks posed by antibiotic-resistant bacteria have stimulated considerable interest in the development of novel antimicrobial strategies, including the use of nanomaterials that can be activated on demand and result in irreversible damage to pathogens. Microwave electric field-assisted bactericidal effects on representative Gram-negative and Gram-positive bacterial strains were achieved in the presence of hybrid polydopamine-silver nanoparticles (PDA-Ag NPs) under low-power microwave irradiation using a resonant cavity (1.3 W, 2.45 GHz). A 3-log reduction in the viability of bacterial populations was observed within 30 minutes which was attributed to the attachment of PDA-Ag NPs and associated membrane disruption in conjunction with the production of intra-bacterial reactive oxygen species (ROS). A synergistic effect between PDA and Ag has been demonstrated whereby PDA acts both as an Ag NP carrier and a microwave enhancer. These properties together with the remarkable adhesivity of PDA are opening a route to design of antibacterial adhesives and surface coatings for prevention of biofilm formation.

Mn-doped Ti-based MOFs for magnetic resonance imaging-guided synergistic microwave thermal and microwave dynamic therapy of liver cancer

Currently, precise ablation of tumors without damaging the surrounding normal tissue is still an urgent problem for clinical microwave therapy of liver cancer. Herein, we synthesized Mn-doped Ti MOFs (Mn-Ti MOFs) nanosheets by in-situ doping method and applied them for microwave therapy. Infrared thermal imaging results indicate Mn-Ti MOFs can rapidly increase the temperature of normal saline, attributing to the porous structure improving microwave-induced ion collision frequency. Moreover, Mn-Ti MOFs show higher 1O2 output than Ti MOFs under 2W of low-power microwave irradiation due to the narrower band-gap after Mn doping. At the same time, Mn endows the MOFs with a desirable T1 contrast of magnetic resonance imaging (r2/r1=2.315). Further, results on HepG2 tumor-bearing mice prove that microwave-triggered Mn-Ti MOFs nearly eradicate the tumors after 14 days of treatment. Our study offers a promising sensitizer for synergistic microwave thermal and microwave dynamic therapy of liver cancer.

Evolution of pore-fracture structure and permeability of coal by microwave irradiation under uniaxial compression

In a natural coal reservoir environment, the coal seam is constrained by in-situ stress and gas pressure. Damage on the coal microstructure due to microwave irradiation (MI) differs significantly different from that under no-load conditions. In this study, the effect of MI on the pore-fracture structure and seepage characteristics of load-constrained coal is investigated using a custom-developed microwave fracturing experimental device, nuclear magnetic resonance test device, and permeability test device. Based on the relationship between microwave and pore-fracture structure parameters and the permeability of loaded coal, the pore-fracture structure evolution and permeability growth law of loaded coal under MI are determined. The results show that the number of micropores in coal decreases and the T2 curve of micropores is shifted to the right under the combined effect of MI and external stress load. The numbers of mesopores, macro-pores, and micro-fractures increase, and the T2 curve exhibits a broader peak span. The pore-fracture structure evolution effect of loaded coal increases with the microwave power and MI time. Under high-power MI, the pore-fracture structure evolution of the loaded coal shows a “decrease - increase – decrease” trend as the stress load increases, whereas a “decrease – increase” trend is shown under low-power MI. Under the same microwave parameters, the permeability of unloaded and loaded coal increases by a maximum of 15.7 and 364.7 times, respectively. In particular, the permeability increases by 3.1–11.4 and 17.8–49.7 times under external stress loads of 4 and 2 MPa, respectively. The combination of high MI power and short MI duration under the same microwave energy facilitates the development of the pore-fracture structure and increases the permeability of loaded coal. Microwaves have a differential thermal effect on mineral in coal, which reduce the physical properties of the coal. Pore-fracture structure and permeability are further enhanced by the stress load.

Study on TiO2 Nanofilm That Reduces the Heat Production of Titanium Alloy Implant in Microwave Irradiation and Does Not Affect Fracture Healing.

Background Metal implants can produce heat and damage adjacent tissues under microwave irradiation, which makes local metal implants in the body a contraindication for microwave therapy. However, with the wide application of titanium alloy implants which have low permeability and low conductivity, this concept has been challenged. Our team members have confirmed through previous research that continuous low-power microwave irradiation does not cause thermal damage to the surrounding tissues of the titanium alloy. Is there any other way to further increase the dose of microwave irradiation while reducing the heat production of titanium alloy implants? In this study, the effect of TiO2 nanofilm on reducing the heat production of titanium alloy implants in microwave field was verified by animal experiments, and the effect of TiO2 nanofilm on fracture healing was observed. Methods 30 rabbits were selected. In the experiment of temperature measurement, 10 rabbits were randomly divided into experimental group (n = 5) and control group (n = 5), and the contralateral lower limb of the rabbits in experimental group was set as the sham operation group. The right femurs in the experimental group were implanted with Ti6Al4V plates coated with TiO2 nanofilm, and the right femurs in the control group were implanted with common titanium alloy plates without TiO2 nanofilm. The same surgical procedure was used in the sham operation group, but no plate was implanted. The temperature of the deep tissue above the metal implant was measured with an anti-interference thermocouple thermometer during 20 minutes of microwave irradiation. The other 20 rabbits were randomly divided into two groups, experimental group (n = 10) and control group (n = 10). The femoral shaft fracture models were established again. Ti6Al4V plates coated with TiO2 nanofilm and common titanium alloy plates were implanted in the two groups, respectively, and both groups were exposed to continuous microwave irradiation with a power of 40 W or 60 W for 30 days after operation. The fracture healing was evaluated by X-ray at 0 day, 14 days, and 30 days after microwave irradiation, respectively. The animals were sacrificed at 30 days after operation for histopathological assessment. Results The temperature in the experimental group, control group, and sham operation group increased significantly after 40 W and 60 W microwave irradiation (2.18 ± 0.15°C~6.02 ± 0.38°C). When exposed to 40 W microwave, the temperature rise of the control group was 4.0 ± 0.34°C, which was significantly higher than that of the experimental group 2.82 ± 0.15°C (P < 0.01) and the sham operation group 2.18 ± 0.33°C (P < 0.01). There was no significant difference in temperature rise between the experimental group and the sham operation group (P = 0.21). When exposed to 60 W microwave, the temperature rise of the control group was 6.02 ± 0.38°C, which was significantly higher than that of the experimental group 3.66 ± 0.14°C (P < 0.01) and sham operation group 2.96 ± 0.22°C (P < 0.01), and there was no significant difference between the experimental group and the sham operation group (P = 0.32). X-ray evaluation showed that there was no significant difference in callus maturity between the experimental group and the control group at 14 days (P = 0.554), but there was significant difference in callus maturity between the two groups at 30 days (P = 0.041). The analysis of bone histologic and histomorphometric data at 30 days was also consistent with this. Conclusion Under the animal experimental condition, compared with the common titanium alloy implant, the TiO2 nanofilm can reduce the heat production of the titanium alloy implant in the 2450 MHz microwave field and has no adverse effect on fracture healing. This study opens up a promising new idea for the application of microwave therapy to metal implants in human body.

Alkoxo bridged heterobimetallic CoIIISnIV compounds with face shared coordination octahedra: Synthesis, crystal structure and cyanosilylation catalysis

The self-assembly reaction of the Schiff base N,N’-ethylenebis(2-hydroxyacetophenoneimine) (H2L), CoCl2··6H2O and [SnPh2Cl2] led to the alkoxo-bridged heteroorganometallic CoIIISnIV complex [{SnPhCl2}(1κO2:2κO2N2-μ-L)(μ-OMe){CoPh}]·CH3OH·H2O (1) or [{SnPhCl2}(1κO2:2κO2N2-μ-L)(μ-OEt){CoPh}] (2) in MeOH or EtOH, respectively. The structures of these complexes are authenticated by single crystal X-ray diffraction analyses. They are derived from an intermetallic (Sn to Co) phenyl shift, leading to face-shared distorted octahedral coordination geometries. The complexes were tested as homogeneous catalysts for the solvent-free cyanosilylation reaction of benzaldehyde with trimethylsilyl cyanide (TMSCN) under low power microwave irradiation at 50°C. They exhibited a high catalytic activity, yielding (for catalyst 1) up to 93% of the cyano-derivative from benzaldehyde in 90 minutes.

Efficient and green synthesis of trisubstituted imidazoles by magnetically nanocatalyst and microwave assisted

Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) were prepared and used as an eco-friendly, reusable, low-cost and efficient catalyst for the synthesis of 2,4,5-trisubstituted imidazoles via three-component reaction of aromatic aldehydes with benzil and ammonium acetate under low power microwave irradiation and solvent-free condition. This one-pot procedure is very simple with good to excellent yields. Easy separation of Fe3O4 MNPs from the reaction mixture by an external magnet and the reusability of the catalyst are the considerable points of the reaction.

Microwave-Polyol Synthesis of Sub-10-nm PbS Nanocrystals for Metal Oxide/Nanocrystal Heterojunction Photodetectors

A rapid microwave-polyol technique is developed to grow bare-surface sub-10-nm lead sulfide (PbS) colloidal nanocrystals (NCs) of uniform size. Growth involves three distinct dynamical stages. PbS NCs homogeneously nucleate and undergo a fast growth process that spontaneously aggregates them into a continuous microstructure of PbS. Next, the interaction of low-power microwave irradiation with the NCs’ dipole moments along different crystallographic axes leads to the development of strain at the NCs’ grain boundaries, which ultimately causes dissociation of the aggregated microstructures into individual uniform-sized PbS NCs. The most distinctive feature of this growth technique is the bare nature and uniform size of the NCs produced. This gives the freedom to fabricate a highly packed NC thin film, which is essential for enhanced charge-transport properties. It simultaneously also precludes the need of undergoing a detrimental solid-state ligand-exchange process, which is indispensably required for casting thin films from conventional counterpart long-aliphatic-ligand-capped NCs. To realize the photosensitivity and charge-transport nature of these microwave-synthesized NCs, we fabricated a lateral heterojunction photoconductor and a phototransistor that work on the principal of electron transfer to the metal oxide layer. The photoconductor exhibits prominent multispectral photosensitivity in the visible region, demonstrating high external quantum efficiency and detectivity of 7.42 × 102% and 1.07 × 1011 jones, respectively. Further, it also shows superior photocurrent generation with respect to the conventional hot-injection-method-synthesized PbS NC-based photoconductor, indicating more efficient inter-NC charge transport in its NC thin film. The unencapsulated photoconductor exhibits a long air-storage lifetime, which reflects air stability of the device and PbS NCs. In addition to the photoconductor, the metal oxide/PbS heterojunction phototransistor also shows superior photosensitivity with a responsivity and a response time of 3 × 10–2A/W and 2.2 s, respectively.

Ketalization of Ketones to 1,3-Dioxolanes and Concurring Self-Aldolization Catalyzed by an Amorphous, Hydrophilic SiO2-SO3H Catalyst under Microwave Irradiation

The amorphous, mesoporous SiO2-SO3H catalyst with a surface area of 115 m2 g-1 and 1.32 mmol H+ per g was very efficient for the protonation of ketones on a 10% (m/m) basis, and the catalyst-bound intermediates can be trapped by polyalcohols to produce ketals in high yields or suffer aldol condensations within minutes under low-power microwave irradiation. The same catalyst can easily reverse the ketalization reaction.

Efficient microwave-assisted diastereoselective synthesis of indole-based 4,5-dihydrofurans via a one-pot, three-component reaction in water

The combination of two or more different heterocyclic moieties in a single molecule would enhance biological activity significantly. The indole and furan scaffolds are promising candidates in drug design, and they have been widely found in natural products and therapeutic agents. Owing to their pharmaceutical importance, there is an urgent need to design rapid, efficient and environmentally benign protocols for the synthesis of indole–dihydrofuran biheterocycles. Herein, we have developed a novel ecofriendly approach for the diastereoselective synthesis of indole-based 4,5-dihydrofurans through a three-component reaction of 3-cyanoacetyl indoles with various aldehydes and N-phenacylpyridinium bromides in the presence of potassium carbonate as an inexpensive and non-toxic base in water under low power microwave irradiation. The findings show that aromatic and heteroaromatic aldehydes tolerated well in this reaction. The products were obtained in 85–98% yields in 4–20 min. The advantages of this method consist of the environmental friendly reaction conditions, use of green solvent and safe base, availability of raw materials, wide range of usable substrates, short reaction times, excellent yields and absence of any tedious workup or purification.

Enhancement of electrochemical performance of nickel cobalt layered double hydroxide@nickel foam with potassium ferricyanide auxiliary electrolyte

Metal oxide nanostructures have been studied widely to overcome the limitations in the capacitance of the carbon-based supercapacitor electrode materials. An electrode with a very porous 3D structure is preferred to facilitate the mass transfer of large electrolyte ions. In this study, highly nanostructured, binder-free Ni-Co-based pseudocapacitive electrodes were synthesized directly on porous 3D structured nickel foam (NF) current collectors using low-power microwave irradiation. The electrochemical performance of the Ni-Co layered double hydroxide (Ni-Co-LDH) showed better performance than Ni-Co oxide (Ni-Co-O) with the further addition of redox additive/active electrolytes, such as K3Fe(CN)6. The specific capacitances of 4664 F g−1 for Ni-Co-LDH and 1758 F g−1 for Ni-Co-O at 5 mA cm−2 in the KOH/K3Fe(CN)6 electrolyte were improved greatly compared to the values of their corresponding materials in the conventional KOH electrolyte (2875 and 250 F g−1, respectively). Interestingly, the Ni-Co-LDH//AC asymmetric device exhibited a specific capacitance of 108.9 F g−1 and an energy density of 38.7 Wh kg−1 with a stability of 61.9% after 5000 cycles. The facile yet cost-effective synthesis of nanostructured electrodes provides a versatile approach for the design of high-performance pseudocapacitive electrodes for future energy-storage systems.

Investigation of Rapid Low-Power Microwave-Induction Heating Scheme on the Cross-Linking Process of the Poly(4-vinylphenol) for the Gate Insulator of Pentacene-Based Thin-Film Transistors.

In this study, a proposed Microwave-Induction Heating (MIH) scheme has been systematically studied to acquire suitable MIH parameters including chamber pressure, microwave power and heating time. The proposed MIH means that the thin indium tin oxide (ITO) metal below the Poly(4-vinylphenol) (PVP) film is heated rapidly by microwave irradiation and the heated ITO metal gate can heat the PVP gate insulator, resulting in PVP cross-linking. It is found that the attenuation of the microwave energy decreases with the decreasing chamber pressure. The optimal conditions are a power of 50 W, a heating time of 5 min, and a chamber pressure of 20 mTorr. When suitable MIH parameters were used, the effect of PVP cross-linking and the device performance were similar to those obtained using traditional oven heating, even though the cross-linking time was significantly decreased from 1 h to 5 min. Besides the gate leakage current, the interface trap state density (Nit) was also calculated to describe the interface status between the gate insulator and the active layer. The lowest interface trap state density can be found in the device with the PVP gate insulator cross-linked by using the optimal MIH condition. Therefore, it is believed that the MIH scheme is a good candidate to cross-link the PVP gate insulator for organic thin-film transistor applications as a result of its features of rapid heating (5 min) and low-power microwave-irradiation (50 W).

Eradication of Cytomegalovirus from Human Milk by Microwave Irradiation: A Pilot Study.

Cytomegalovirus (CMV)-infected human milk (HM) can lead to significant CMV morbidity and mortality in preterm very-low-birth weight infants. The eradication of CMV in HM while preserving its properties poses a major clinical challenge. We aimed to compare two methods used to neutralize the virus in HM, one recognized as partially effective (freezing) and another not tested to date (microwave exposure). We sampled HM from 31 CMV-seropositive mothers whose infants were hospitalized at the Lis Maternity Hospital. Fifteen samples that were positive for CMV antigen were divided into five 5 mL aliquots: the first a control, the second was frozen at -20°C for 1 day, the third was frozen at -200°C for 3 days, and the fourth and fifth aliquots were exposed for 30 seconds to microwave radiation at a low-power setting (500 W) and high-power setting (750 W), respectively. Only microwave radiation at a high-power setting led to complete neutralization of CMV in all samples. Low-power microwave irradiation had a 13% failure rate while 3-day freezing and 1-day freezing had failure rates of 7% and 20%, respectively. It is possible to eradicate CMV successfully in HM by using microwave radiation at a high-power setting. Further studies are needed to evaluate the effect of microwave heating on breast milk properties.

Rapid surface functionalization of carbon fibres using microwave irradiation in an ionic liquid

Carbon fibre surfaces have been successfully modified using molecular grafting under low power microwave irradiation (20 W) in both 1,2-dichlorobenzene and emimTFSI. Results showed an improved IFSS by 18% for organic solvent and 28% for ionic liquid.

The effect of microwave irradiation on transglycosylation pathway of stevioside with starches or cyclodextrins catalyzed by a cyclodextrin glucanotransferase

Microwave irradiation may alternate reaction specifity in multipath reactions. In this experiment, transglycosylation of stevioside with starches or α/β-cyclodextrin (CD) reached reaction equilibrium only in 3min under low power microwave irradiation, when 10U/g stevioside of a CGTase was applied. Microwave irradiation does not dramatically affect the transglycosylation pathway of the starches with stevioside, but it remarkably affects the transglycosylation pathway of α/β-CD onto stevioside. Unlike the case under conventional heating, the transformation between α-CD and β-CD was dramatically declined by microwave. With α/β-cyclodextrins as glycosyl donor, highly grafted products were diminished under microwave irradiation. Gelatinized starch produced much more cyclodextrins than hydrolyzed starch did, which made higher stevioside conversion with gelatinized starch.

Testing Innovative Technique Based on Microwave Irradiation, for Stimulating Common Bean Germination and Development

In the last decades a new goal for agriculture is to develop environmentally friendly innovative technologies. One of the interest solutions, in perspective, is the treatment of plants with low power microwave irradiation in order to obtain a higher and healthier production. This approach could also contribute to mitigation of harmful effects produced by excessive use of chemical products in treatment of seeds and also field culture phytoprotection. Investigating effects of microwave irradiation, on the germination of common bean ( Phaseolus vulgaris L. cv. Ardeleana) seeds, and on the growth and development of bean plantules, in specific experimental conditions. The trial was developed within Laboratories of the Advanced Research Centre for Environmental Protection and Assessment of Life Quality from USAMV Cluj-Napoca. The growing experiment of 10 - 8 days (with 49 individuals each) was developed until the seeds have grown up to 15 cm height, in conditions of microwave irradiated and no irradiated conditions. The studied parameters were: length of stems, length of roots, and seedling vigour index. Data were statistically processed with STATISTICA v 6.0 Office. The studied parameters were quantified by biometric approach (length of stems and roots). The use of low power microwave irradiation in germination of common bean in laboratory conditions may be taken into consideration for large scale cultivation. Further research is needed in order to establish appropriate practices for the success of this innovative technique.

Rapid Microbial Lysing and DNA Fragmentation by Microwave Focusing

Bacterial infections are a major health problem worldwide. Identification of disease-causing organisms by culture-based approaches is time-consuming and often lacks sensitivity. Molecular approaches such as PCR and microwave-accelerated metal-enhanced fluorescence (MAMEF) assays1, are more sensitive and faster than traditional culture-based approaches, but require isolation of the target DNA. In order to determine the effect of both boiling and microwave irradiation on microbial lysing and DNA fragmentation, cultures of Neisseria gonorrhoeae and Listeria monocytogenes (108 CFU /mL) were either boiled (range 40° - 70°C) or lysed in a 900-watt microwave on isolator-mounted microscope slides, both with and without the assistance of disjointed antenna gold bow-tie structures. The temperatures of cultures were obtained prior to and after lysing and the resulting lysate cultured on selective agar plates. DNA isolation and fragmentation efficiency were determined by gel electrophoresis and PCR. N. gonorrhoeae lysed at a lower temperature (°C) than L. monocytogenes. Microbial lysing and DNA fragmentation was more effectively carried out in the presence dis-jointed gold triangle structures, but only when small sample volume were used. Standard boiling was successful for bacterial lysing and DNA fragmentation, but required higher temperatures and longer times than microwave focusing. PCR results suggest that low power microwave irradiation is ideal for PCR methods while higher microwave powers are required to generate DNA fragments ideal for MAMEF analysis. Microbial lysing and DNA fragmentation can be achieved by either boiling or microwave, but microwave lysing is more efficient for DNA fragmentation and is significantly faster. Microwave lysing is the recommended method when rapid isolation and DNA fragmentation is required.1Melendez, et at. (2013). Blind Evaluation of the Microwave-Accelerated Metal-Enhanced Fluorescence Ultrarapid and Sensitive Chlamydia Trachomatis test by use of Clinical Samples, Journal of Clinical Microbiology, 51(9), 2913-2920.

Rapid synthesis of a flower-like ZnO/rGO/Ag micro/nano-composite with enhanced photocatalytic performance by a one-step microwave method

Flower-like ZnO/rGO/Ag micro/nano-composites (MNCs) have been engineered by a one-step microwave technique using graphene oxide, AgNO3 and Zn(CH3COO)2 as raw materials without adding any external toxic reagent. This is a facile and rapid process requiring only low power microwave irradiation (120 W). Various characterization results showed that the flower-like ZnO/rGO/Ag MNCs consisted of a ZnO nanosheet and Ag nanoparticles and reduced graphene oxide (rGO) deposited on ZnO nanosheet surface. The composite shows an enhanced and faster ultraviolet and simulated daylight photocatalytic property, i.e. 92.73% and 70.43% degradation of methyl orange in 20 minutes as compared to the values of 70.91% and 60.82%, 55.48% and 50.61% by bare ZnO and rGO/ZnO, respectively. The enhanced photocatalytic property is attributed to an efficient charge transfer process from ZnO to both Ag and rGO. This method would be beneficial for synthesizing efficient ZnO-based ternary photocatalysts with a combination of metal and rGO.

5-color multiplexed microwave-accelerated metal-enhanced fluorescence: detection and analysis of multiple DNA sequences from within one sample well within a few seconds.

We present a potentially highly sensitive and selective bio-assay for the potential detection of any five different DNA sequences from one sample in one well. The assay is based on a DNA "rapid catch and signal" (DNA-RCS) technology developed for the detection of different DNA sequences from a sample well area. Our signal amplification utilizes the metal-enhanced fluorescence (MEF) of dyes attached to the probe-DNAs, which hybridizes with the pre-formed mixture of anchor-DNA scaffolds on silver island films (SiFs). Low-power microwave irradiation accelerates both the formation of the anchor-DNA scaffold on the SiF-surface and anchor/probe DNA hybridization, i.e. "rapid catch" of target DNAs from a bulk solution, decreasing the assay run time from hours to only a few seconds. Localization of signaling dye-labels close to the SiFs make them extremely photostable, which allows for collecting/integrating the signal over a long time period. To demonstrate a 5 color DNA assay (5-plex) we have used a range of readily available Alexa™ dyes. Advantages and perspectives of the RCS-technologies ability to detect 5 different DNA sequences from within one plate-well are discussed.

SYNTHESIS OF MESOPOROUS MCM-41 MATERIALS WITH LOW-POWER MICROWAVE HEATING

Crystalline, high-surface-area, hexagonal mesoporous MCM-41 having uniform pore sizes and good thermal stability was successfully synthesized at 90°–120°C in 30 min using low-power microwave irradiation. This appears to be the first comprehensive and quantitative investigation of the comparatively rapid synthesis of mesoporous MCM-41 using low-power microwave heating of 80 W (90°C) and 120 W (120°C). The influence of reaction temperature and the duration of heating were carefully investigated, and the calcined MCM-41 materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA, and FT-IR. The mesoporous MCM-41 product synthesized in 30 min at 120 W and calcined at 550°C had a very high surface area of 1438 m2/g and was highly ordered, containing uniform pores with diameters in the range of 3.5–4.5 nm. The wall thickness of the materials highly depended on the power of the microwave energy used during synthesis. Synthesis of the mesoporous MCM-41 products at 120°C resulted in a structure with thinner walls. The mesoporous MCM-41 materials synthesized in the present work had good thermal stability.

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids

We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D 13C–13C exchange spectroscopy to probe the peptide backbone torsion angles (ϕ, ψ) in a series of selectively 13C-labeled 40-residue β-amyloid (Aβ1–40) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39T and 8K, using a static double-resonance NMR probe and low-power microwave irradiation at 264GHz. In frozen solutions of Aβ1–40 fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16–21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl 13C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous 13C lineshapes are incorporated in the simulations. The experimental 2D 13C–13C exchange spectra place constraints on the ϕ and ψ angles between the two carbonyl labels. Although the data are not sufficient to determine ϕ and ψ uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D 13C–13C exchange spectra can be obtained from a 3.5mg sample of Aβ1–40 fibrils in 4h or less, despite the broad 13C chemical shift anisotropy line shapes that are observed in static samples.