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The sensitivity of electron spin resonance has been improved up to the quantum limit through the use of a Josephson parametric microwave amplifier combined with high-quality-factor superconducting microresonators cooled at millikelvin temperatures. The detection and characterization of paramagnetic species by electron spin resonance (ESR) spectroscopy is widely used throughout chemistry, biology and materials science 1 , from in vivo imaging 2 to distance measurements in spin-labelled proteins 3 . ESR relies on the inductive detection of microwave signals emitted by the spins into a coupled microwave resonator during their Larmor precession. However, such signals can be very small, prohibiting the application of ESR at the nanoscale (for example, at the single-cell level or on individual nanoparticles). Here, using a Josephson parametric microwave amplifier combined with high-quality-factor superconducting microresonators cooled at millikelvin temperatures, we improve the state-of-the-art sensitivity of inductive ESR detection by nearly four orders of magnitude 4 , 5 . We demonstrate the detection of 1,700 bismuth donor spins in silicon within a single Hahn 6 echo with unit signal-to-noise ratio, reduced to 150 spins by averaging a single Carr–Purcell–Meiboom–Gill sequence 7 . This unprecedented sensitivity reaches the limit set by quantum fluctuations of the electromagnetic field instead of thermal or technical noise, which constitutes a novel regime for magnetic resonance. The detection volume of our resonator is ∼0.02 nl, and our approach can be readily scaled down further to improve sensitivity, providing a new versatile toolbox for ESR at the nanoscale.

Electron spin resonance (ESR) dosimetry was applied to human tooth enamel in order to obtain individual absorbed doses for victims of the Hiroshima bomb who lived in the ‘black rain’ area. The so-called ‘black rain’ fell in the form of precipitation on the western part of Hiroshima city and the northwestern suburbs within a few hours after the explosion of the atomic bomb on 6 August 1945, and exposed the population in this area. Only three tooth samples were collected from this area. Since the teeth were located at positions 1, 2 and 4, only the lingual portion was used for the analysis. The results showed that the excess dose after subtracting natural radiation for one (position 4; hh1) was background, for the second (position 2; hh2) it was 133 mGy, and for the other (position 1; hh3) it was 243 mGy. Based on these results, we further investigated the radiation dose attributed to dental X-rays and head CT scan. Such dose of the hh3 radiographic examination was estimated to be 57–160 mGy, which implies an additional exposure around 135 mGy after subtraction. On the other hand, the dose data of hh1 after subtracting dental X-rays was negative. This may mean that such additional doses are an overestimation. In addition, the effect of sunlight should be considered, which is the same direction of overestimation. As a result, the residual dose of 140 mGy suggests the inclusion of radiation from the ‘black rain.’

In this research, the porous polymer structures (IPN) were made from natural isoprene rubber (NR) and poly(methyl methacrylate) (PMMA). The effects of molecular weight and crosslink density of polyisoprene on the morphology and miscibility with PMMA were determined. Sequential semi-IPNs were prepared. Viscoelastic, thermal and mechanical properties of semi-IPN were studied. The results showed that the key factor influencing the miscibility in semi-IPN was the crosslinking density of the natural rubber. The degree of compatibility was increased by doubling the crosslinking level. The degree of miscibility at two different compositions was compared by simulations of the electron spin resonance spectra. Compatibility of semi-IPNs was found to be more efficient when the PMMA content was less than 40 wt.%. A nanometer-sized morphology was obtained for a NR/PMMA ratio of 50/50. Highly crosslinked elastic semi-IPN followed the storage modulus of PMMA after the glass transition as a result of certain degree of phase mixing and interlocked structure. It was shown that the morphology of the porous polymer network could be easily controlled by the proper choice of concentration and composition of crosslinking agent. A dual phase morphology resulted from the higher concentration and the lower crosslinking level. This was used for developing porous structures from the elastic semi-IPN. The mechanical performance was correlated with morphology, and the thermal stability was comparable with respect to pure NR. Investigated materials might be interesting for use as potential carriers of bioactive molecules aimed for innovative applications such as in food packaging.

Thermoluminescence dating of fire-heated flint artefacts, and directly associated newly discovered remains of Homo sapiens , indicate that the Middle Stone Age site of Jebel Irhoud in Morocco is 383–247 thousand years old. Early dawn for Homo sapiens The exact place and time that our species emerged remains obscure because the fossil record is limited and the chronological age of many key specimens remains uncertain. Previous fossil evidence has placed the emergence of modern human biology in eastern Africa around 200,000 years ago. In this issue of Nature , Jean-Jaques Hublin and colleagues report new human fossils from Jebel Irhoud, Morocco; their work is accompanied by a separate report on the dating of the fossils by Shannon McPherron and colleagues. Together they report remains dating back 300,000–350,000 years. They identify numerous features, including a facial, mandibular and dental morphology, that align the material with early or recent modern humans. They also identified more primitive neurocranial and endocranial morphology. Collectively, the researchers believe that this mosaic of features displayed by the Jebel Irhoud hominins assigns them to the earliest evolutionary phase of Homo sapiens . Both papers suggest that the evolutionary processes behind the emergence of modern humans were not confined to sub-Saharan Africa. The timing and location of the emergence of our species and of associated behavioural changes are crucial for our understanding of human evolution. The earliest fossil attributed to a modern form of Homo sapiens comes from eastern Africa and is approximately 195 thousand years old 1 , 2 , therefore the emergence of modern human biology is commonly placed at around 200 thousand years ago 3 , 4 . The earliest Middle Stone Age assemblages come from eastern and southern Africa but date much earlier 5 , 6 , 7 . Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of H. sapiens 8 . A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible. These ages are also consistent with the faunal and microfaunal 9 assemblages and almost double the previous age estimates for the lower part of the deposits 10 , 11 . The north African site of Jebel Irhoud contains one of the earliest directly dated Middle Stone Age assemblages, and its associated human remains are the oldest reported for H. sapiens . The emergence of our species and of the Middle Stone Age appear to be close in time, and these data suggest a larger scale, potentially pan-African, origin for both.

Here we introduce chiLife, a Python package for site-directed spin label (SDSL) modeling for electron paramagnetic resonance (EPR) spectroscopy, in particular double electron–electron resonance (DEER). It is based on in silico attachment of rotamer ensemble representations of spin labels to protein structures. chiLife enables the development of custom protein analysis and modeling pipelines using SDSL EPR experimental data. It allows the user to add custom spin labels, scoring functions and spin label modeling methods. chiLife is designed with integration into third-party software in mind, to take advantage of the diverse and rapidly expanding set of molecular modeling tools available with a Python interface. This article describes the main design principles of chiLife and presents a series of examples.

Magnetic resonance spectroscopy of single biomolecules under near-physiological conditions could substantially advance understanding of their biological function, but this approach remains very challenging. Here we used nitrogen-vacancy centers in diamonds to detect electron spin resonance spectra of individual, tethered DNA duplexes labeled with a nitroxide spin label in aqueous buffer solutions at ambient temperatures. This work paves the way for magnetic resonance studies on single biomolecules and their intermolecular interactions in native-like environments.

Impact by hailstone, volcanic rock, bird strike, or also dropping tools can cause damage to aircraft materials. For maximum safety, the goal is to increase Charpy impact strength (auc) of a carbon-fiber-reinforced thermoplastic polyphenylene sulfide polymer (CFRTP-PPS) composite for potential application to commercial aircraft parts. The layup was three cross-weave CF plies alternating between four PPS plies, [PPS-CF-PPS-CF-PPS-CF-PPS], designated [PPS]4[CF]3. To strengthen, a new process for CFRP-PPS was employed applying homogeneous low voltage electron beam irradiation (HLEBI) to both sides of PPS plies prior to lamination assembly with untreated CF, followed by hot press under 4.0 MPa at 573 K for 8 min. Experimental results showed a 5 kGy HLEBI dose was at or near optimum, increasing auc at each accumulative probability, Pf. Optical microscopy of 5 kGy sample showed a reduction in main crack width with significantly reduced CF separation and pull-out; while, scanning electron microscopy (SEM) and electron dispersive X-ray (EDS) mapping showed PPS adhering to CF. Electron spin resonance (ESR) of a 5 kGy sample indicated lengthening of PPS chains as evidenced by a reduction in dangling bond peak. It Is assumed that 5 kGy HLEBI creates strong bonds at the interface while strengthening the PPS bulk. A model is proposed to illustrate the possible strengthening mechanism.

Many RNA-binding proteins undergo liquid–liquid phase separation, which underlies the formation of membraneless organelles, such as stress granules and P-bodies. Studies of the molecular mechanism of phase separation in vitro are hampered by the coalescence and sedimentation of organelle-sized droplets interacting with glass surfaces. Here, we demonstrate that liquid droplets of fused in sarcoma (FUS)—a protein found in cytoplasmic aggregates of amyotrophic lateral sclerosis and frontotemporal dementia patients—can be stabilized in vitro using an agarose hydrogel that acts as a cytoskeleton mimic. This allows their spectroscopic characterization by liquid-phase NMR and electron paramagnetic resonance spectroscopy. Protein signals from both dispersed and condensed phases can be observed simultaneously, and their respective proportions can be quantified precisely. Furthermore, the agarose hydrogel acts as a cryoprotectant during shock-freezing, which facilitates pulsed electron paramagnetic resonance measurements at cryogenic temperatures. Surprisingly, double electron–electron resonance measurements revealed a compaction of FUS in the condensed phase. An agarose hydrogel mimicking cytoskeleton stabilizes protein liquid droplets and enables precise quantification of protein percentage in phase-separated droplets and in the dispersed phases as well as intramolecular distances via NMR and EPR.

Electron paramagnetic resonance (EPR) is an excellent choice for detecting free radicals in biological samples. Biologically relevant radicals are extremely short-lived and cannot be detected directly, emphasizing the need for an appropriate compound to generate stable adducts that can be measured by EPR. Spin trapping with nitrone compounds like 5,5-dimethyl-1-pyrroline N-oxide (DMPO) is a method commonly employed for detecting free radicals. However, due to the instability of nitrone radical adducts, using the cell-permeable 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethyl pyrrolidine (CMH) appears to be a more effective approach within biological tissues. Here, we compare the use of DMPO and CMH to detect the most abundant reactive oxygen species radical, superoxide ( O 2 ⋅ - ), in zebrafish and present an optimized protocol for performing EPR with a CMH spin probe in both zebrafish hearts and larvae. Together, our data suggest that EPR using the CMH probe is a reliable method to detect O 2 ⋅ - in zebrafish pathologies linked to oxidative stress, such as cardiovascular diseases.

We report an approach that extends the applicability of ultrasensitive force-gradient detection of magnetic resonance to samples with spin-lattice relaxation times (T ₁) as short as a single cantilever period. To demonstrate the generality of the approach, which relies on detecting either cantilever frequency or phase, we used it to detect electron spin resonance from a T ₁ = 1 ms nitroxide spin probe in a thin film at 4.2 K and 0.6 T. By using a custom-fabricated cantilever with a 4 μm-diameter nickel tip, we achieve a magnetic resonance sensitivity of 400 Bohr magnetons in a 1 Hz bandwidth. A theory is presented that quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. Good agreement was found between nitroxide T ₁ 's measured mechanically and inductively, indicating that the cantilever magnet is not an appreciable source of spin-lattice relaxation here. We suggest that the new approach has a number of advantages that make it well suited to push magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule to single-spin sensitivity.