Surface NMR using quantum sensors in diamond

NMR is a noninvasive, molecular-level spectroscopic technique widely used for chemical characterization. However, it lacks the sensitivity to probe the small number of spins at surfaces and interfaces. Here, we use nitrogen vacancy (NV) centers in diamond as quantum sensors to optically detect NMR signals from chemically modified thin films. To demonstrate the method’s capabilities, aluminum oxide layers, common supports in catalysis and materials science, are prepared by atomic layer deposition and are subsequently functionalized by phosphonate chemistry to form self-assembled monolayers. The surface NV-NMR technique detects spatially resolved NMR signals from the monolayer, indicates chemical binding, and quantifies molecular coverage. In addition, it can monitor in real time the formation kinetics at the solid–liquid interface. With our approach, we show that NV quantum sensors are a surface-sensitive NMR tool with femtomole sensitivity for in situ analysis in catalysis, materials, and biological research.

The characterization of surface processes at the molecular level is essential for understanding fundamental processes in industrial catalysis, energy conversion, electronic circuits, targeted drug delivery, and biosensing (1). However, many analytical techniques used in surface science are inaccessible under ambient or chemically relevant conditions. Therefore, it remains challenging to perform chemical analysis under the conditions in which these processes occur (2, 3). Commonly used surface sensitive methods, such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and secondary ion mass spectroscopy can perform chemical analysis but require ultra-high vacuum and expensive equipment (4). Great efforts have been devoted to extending XPS analysis to near ambient conditions (2). Indeed, both near-ambient pressure XPS and extended X-ray absorption fine structure have significantly expanded the applicability of these X-ray–based techniques for understanding reaction mechanisms at chemically active interfaces (2, 5). However, both methods require intense synchrotron radiation to achieve high sensitivity and resolution, which limits their practical accessibility and increases their cost. State-of-the-art surface-sensitive spectroscopy techniques, such as sum frequency generation and second harmonic generation, can perform analysis under ambient conditions but require technically complex equipment such as femtosecond lasers (6). Even with all these techniques available, molecular dynamics or chemical reaction kinetics at surfaces are still challenging to probe experimentally (7) (SI Appendix, Supplementary Note 1).NMR spectroscopy is one of the major tools for chemical and structural analysis in chemistry, biology, and materials science. Solid-state NMR in particular (8) has advanced understanding of a range of systems, including metal organic frameworks (9), batteries (10), and catalysts (11). However, sensitivity remains a challenge for traditional NMR spectroscopy, making studies at surfaces difficult because of the limited numbers of nuclear spins. Recently, surface-enhanced NMR spectroscopy (DNP-SENS) relying on hyperpolarization such as dynamic nuclear polarization (12, 13) or xenon-based techniques (14) gained research momentum and enabled probing spins located at surfaces. However, even in highly porous materials with greater than 1,000 m²/g surface area, the concentration of NMR-active nuclei of interest often remains low (e.g., 1 mmol of surface atoms/g), which requires long averaging times to obtain solid-state NMR spectra with reasonable signal-to-noise ratios (SNR) (12) (SI Appendix, Supplementary Note 2).Here, we demonstrate the use of quantum sensors in diamond as a surface-sensitive spectroscopy technique that works at ambient conditions and can probe planar interfaces on the microscopic length scale with far greater sensitivity (femtomoles, see Materials and Methods) than conventional NMR. The spectroscopic technique relies on the nitrogen vacancy (NV) point defect, consisting of a nitrogen impurity (N) and an adjacent vacancy (V) in the carbon lattice of diamond. These spin-1 defects allow for optical detection of magnetic resonance and have been established as highly sensitive nanoscale magnetic field sensors (15, 16). Near-surface NV centers are sensitive to magnetic fields from the Larmor precession of nuclei from samples positioned outside of the diamond. This enables nanoscale NMR detection—even down to a single molecule (17) or spin (18, 19). The measurement volume of such NV sensors (20, 21) corresponds to a hemisphere whose radius is roughly their depth below the surface in the diamond lattice (e.g., 5 to 10 nm). At this small length scale, the thermal polarization of the nuclear spins can be neglected since spin noise dominates for a small number of spins (22, 23). For that reason, the NMR signal strength is independent of the applied magnetic field B₀, reducing experimental complexity and costs, which makes the technique accessible to a broader community. Previously published nanoscale NV-NMR experiments detected NMR signals from either bulk samples [such as viscous oils (21, 22, 24)] or samples tethered to (17) or placed directly on the diamond surface (25). In this work, we propose the use of NV centers in diamond combined with state-of-the-art thin film deposition techniques as a general platform to detect NMR signals with high sensitivity and spatial resolution even from nondiamond surfaces. This approach is general and allows for the probing of a variety of surfaces and interfaces with NMR, thereby enabling their chemistry to be explored. Here, we use atomic layer deposition (ALD), a technology that can be applied to synthesize films of a wide variety of materials with high thickness precision to coat the diamond with amorphous aluminum oxide (Al₂O₃). Al₂O₃ provides an exemplary surface of high technical relevance in optoelectronic applications and acts as structural support in various catalytic processes (26). In a proof-of-concept study for this surface-sensitive spectroscopic technique, we probe the chemical modification of the Al₂O₃ surface with phosphonate anchoring during the formation of a self-assembling monolayer (SAM) (27).     

Increased Salt Intake Decreases Diet-Induced Thermogenesis in Healthy Volunteers: A Randomized Placebo-Controlled Study

High salt intake ranks among the most important risk factors for noncommunicable diseases. Western diets, which are typically high in salt, are associated with a high prevalence of obesity. High salt is thought to be a potential risk factor for obesity independent of energy intake, although the underlying mechanisms are insufficiently understood. A high salt diet could influence energy expenditure (EE), specifically diet-induced thermogenesis (DIT), which accounts for about 10% of total EE. We aimed to investigate the influence of high salt on DIT. In a randomized, double-blind, placebo-controlled, parallel-group study, 40 healthy subjects received either 6 g/d salt (NaCl) or placebo in capsules over 2 weeks. Before and after the intervention, resting EE, DIT, body composition, food intake, 24 h urine analysis, and blood pressure were obtained. EE was measured by indirect calorimetry after a 12 h overnight fast and a standardized 440 kcal meal. Thirty-eight subjects completed the study. Salt intake from foods was 6 g/d in both groups, resulting in a total salt intake of 12 g/d in the salt group and 6 g/d in the placebo group. Urine sodium increased by 2.29 g/d (p < 0.0001) in the salt group, indicating overall compliance. The change in DIT differed significantly between groups (placebo vs. salt, p = 0.023). DIT decreased by 1.3% in the salt group (p = 0.048), but increased by 0.6% in the placebo group (NS). Substrate oxidation indicated by respiratory exchange ratio, body composition, resting blood pressure, fluid intake, hydration, and urine volume did not change significantly in either group. A moderate short-term increase in salt intake decreased DIT after a standardized meal. This effect could at least partially contribute to the observed weight gain in populations consuming a Western diet high in salt.     

Viscoelastic Polyurethane Foams for Use as Auxiliary Materials in Orthopedics

One of the essential factors in prostheses is their fitting. To assemble a prosthesis with the residual limb, so-called liners are used. Liners used currently are criticized by users for their lack of comfort, causing excessive sweating and skin irritation. The objective of the work was to develop viscoelastic polyurethane foams for use in limb prostheses. As part of the work, foams were produced with different isocyanate indexes (0.6–0.9) and water content (1, 2 and 3 php). The produced foams were characterized by scanning electron microscopy, computer microtomography, infrared spectroscopy, thermogravimetry and differential scanning calorimetry. Measurements also included apparent density, recovery time, rebound elasticity, permanent deformation, compressive stress value and sweat absorption. The results were discussed in the context of modifying the foam recipe. The performance properties of the foams, such as recovery time, hardness, resilience and sweat absorption, indicate that foams that will be suitable for prosthetic applications are foams with a water content of 2 php produced with an isocyanate index of 0.8 and 0.9.     

Palmatine: A review of pharmacological properties and pharmacokinetics

The aim of this review is to collect together the results of the numerous studies over the last two decades on the pharmacological properties of palmatine published in scientific databases like Scopus and PubMed, which are scattered across different publications. Palmatine, an isoquinoline alkaloid from the class of protoberberines, is a yellow compound present in the extracts from different representatives of Berberidaceae, Papaveraceae, Ranunculaceae, and Menispermaceae. It has been extensively used in traditional medicine of Asia in the treatment of jaundice, liver‐related diseases, hypertension, inflammation, and dysentery. New findings describe its possible applications in the treatment of civilization diseases like central nervous system‐related problems. This review intends to let this alkaloid come out from the shade of a more frequently described alkaloid: berberine. The toxicity, pharmacokinetics, and biological activities of this protoberberine alkaloid will be developed in this work.     

Motor Unit Fatigability following Chronic Carnosine Supplementation in Aged Rats

Studies suggest that carnosine (beta-alanyl-L-histidine) is effective in treating neuromuscular diseases associated with aging, but there is still a need to clarify its role in motor units (MUs) function during aging. In this study, 40 male Wistar rats aged 15 months were randomly assigned to a control or to two experimental groups in which 0.1% carnosine supplementation was performed for 10 or 34 weeks. After 34 weeks, we examined fast fatigable (FF), fast fatigue-resistant (FR) and slow (S) MUs’ force properties and fatigability, as well as antioxidant potential, advanced glycation end products, activity of enzymes, and histidyl dipeptides content in the medial gastrocnemius muscle. Short- and long-term carnosine supplementation maintained the force of FF MUs at a higher level during its rapid decline seen from the initial 10 to 70 s of the fatigue test. In FF, especially long-term, and in FR MUs, especially short-term, carnosine supplementation resulted in less rapid force decline during the initial 70 s of the second fatigue protocol. Carnosine supplementation did not change muscle antioxidant potential and mortality rate (~35% in all groups), nor muscle mass with aging. Moreover, instead of the expected increase, a decrease in histidyl dipeptides by ~30% in the red portion of medial gastrocnemius muscle after long-term supplementation was found. After chronic carnosine supplementation, the specific changes in fatigue resistance were observed in FF and FR units, but not in S MU types that were not accompanied by an improvement of antioxidant potential and activity of glycolytic or oxidative enzymes in aged rats. These observations indicate that carnosine supplementation during aging may generate different physiological adaptations which should be considered as an important factor when planning treatment strategies.     

Extensive endometriosis surgery: rASRM and Enzian score independently relate to post-operative complication grade

Archives of Gynecology and Obstetrics - We aimed to assess post-operative complications based on the Clavien–Dindo classification system following routine laparoscopic treatment of all stages...     

Increased Neutrophil-to-Lymphocyte Ratio is Associated with Unfavorable Functional Outcome in Acute Ischemic Stroke

Neurocritical Care - Inflammatory response is the hallmark of secondary brain injury in stroke patients. Neutrophil-to-lymphocyte ratio (NLR) emerged as a marker for functional outcome in several...