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In this study, a low field nuclear magnetic resonance (LF-NMR) homogeneous sensor was constructed for detection of Escherichia coli (E. coli) based on the copper metabolism of E. coli triggered click reaction. When live E. coli was present, a large amount of Cu2+ ions were transformed into Cu+ via copper metabolism, which then catalyzed a Cu+-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between two materials, azide group modified gadolinium oxide nanorods (Gd 2 O 3 -Az) and PA-GO@Fe 3 O 4 i.e., graphene oxide (GO) loaded with large amounts of alkynyl (PA) groups and Fe 3 O 4 nanoparticles simultaneously. After magnetic separation, unbound Gd 2 O 3 -Az was dissolved by added hydrochloric acid (HCl) to generate homogeneous Gd3+ solution, enabling homogeneous detection of E. coli. Triple signal amplification was achieved through the CuAAC reaction induced by E. coli copper metabolism, functional nanomaterials, and HCl assisted homogeneous detection. Under the optimal experimental conditions, the linear range and limit of detection (LOD) for E. coli were 10–1.0 × 107 CFU/mL and 3.5 CFU/mL, respectively, and the relative standard deviations (RSDs) were all less than 2.8 %. In addition, the sensor has satisfactory selectivity, stability and practical sample application capability, providing a new approach for the LF-NMR detection of food-borne pathogenic bacteria. [Display omitted] • Triple signal amplification of the sensor was realized for detection of E. coli. • E. coli metabolism-mediated click chemistry was introduced to the LF-NMR sensor. • Acidolysis of signal units from nanomaterials to ions for homogeneous detection. • Homogeneous detection mediated by pure chemical systems to ensure precision and accuracy. [ABSTRACT FROM AUTHOR]

Based on superparamagnetic nanoparticles, a responsive polyacrylamide hydrogel self-assembled by nucleic acid hairpin hybridization chain reaction was designed, and a universal low field nuclear magnetic resonance sensing platform was successfully constructed. As the target was gradually added, the hydrogel coating on the surface of the magnetic nanoparticle was opened layer by layer through binding with the aptamer, which specifically bonded thereto, causing different degrees of exposure of the magnetic nanoparticle, resulting in changes of low field nuclear magnetic resonance signals. This method was originally applied to the rapid detection of adenosine triphosphate (ATP), and the versatility of the method was verified using polychlorinated biphenyl 77 (PCB77). This method had the advantage of being fast, convenient, and low cost, and it can be easily operated with high repeatability. This universal method can detect a variety of targets by replacing aptamers and may be useful in controlling food quality and for rapidly detecting cancer cells in vitro. Image 1 • Ultra-sensitive aptasensor was constructed based on LF-NMR technology and hydrogel-coated superparamagnetic particles. • Signal amplification was achieved by designed novel self-assembled hydrogel probes and superparamagnetic particles. • The method had the characteristics of fast, sensitive, non-destructive and repeatable. • This aptasensor achieved investigation of ATP levels in water samples with detection limits of 0.1961 mg/ml. • This method can be applied to the detection of multiple targets by designing recognition probes. [ABSTRACT FROM AUTHOR]

• The pore structure characteristics of ECC incorporating RS were investigated. • MIP and NMP were employed to examine the pore structure of the ECC. • The mechanical properties of ECC were elucidated on the basis of micromorphological and pore structure characteristics. The mechanical properties of recycled sand (RS) modified ECC are intimately linked to its pore structure characteristics, but the internal pore size and distribution of RS modified ECC and its impact mechanism on the mechanical properties are still unclear. This study employed mercury intrusion porosimetry (MIP) and low field nuclear magnetic resonance (LF-NMR) techniques to analyze the pore structure of ECC incorporating RS. Furthermore, compression and tension mechanical experiments were conducted to investigate the correlation between the evolution of pore structure and mechanical properties of ECC incorporating RS. The findings demonstrate that the addition of RS increases the porosity of ECC. When replacement ratio of RS is 100 %, the volume fraction of pores decreases within the range of 10 nm to 100 nm , whereas it exhibits an increasing trend within a ranging from 100 nm to 1 μ m. The incorporation of RS results in a decrease of the volume fraction of gel pores and the increase of capillary pores in ECC owing to its high-water absorption and porous, as well as the reduction of calcium-silicate-hydrate (C-S-H) due to the surface attached old mortar. Therefore, addition of RS lead to a reduction in both the compressive strength and tensile strength of ECC. However, as a result of the pore structural flaw inherent in the recycled fine aggregate, the occurrence of multi-crack cracking, induced by interfacial imperfections between the recycled fine aggregate and matrix, contributing to development of cracks in ECC and thus enhancing its tensile strain capacity. [ABSTRACT FROM AUTHOR]

The molecular weight is an important indicator for assessing the aging of polymers. However, existing methods for characterizing the molecular weight of polymers involve complex procedures and destructive tests. Therefore, efficient, rapid, and non-destructive testing methods would be a key development in material degradability evaluation. In this paper, we studied the thermo-oxidative aging process of polybutylene adipate terephthalate (PBAT) using a low-field nuclear magnetic resonance (LF-NMR) analysis method. The degradation mechanism of PBAT during thermo-oxidative aging is characterized by its low-field nuclear magnetic resonance decay curve and inversion curve. A two-component LF-NMR fitting analysis reveals that the thermo-oxidative degradation of PBAT conforms to a random fracture mechanism. Furthermore, a correlation between number average molecular weight and LF-NMR relaxation time during thermo-oxidative degradation of PBAT was constructed, with a correlation coefficient R2 greater than 0.97. The error between the correlation equation used in the molecular weight detection of PBAT and the actual test is less than 10%, indicating that it is feasible and reliable to characterize the number average molecular weight of materials by applying the LF-NMR relaxation time. • A non-destructive method for characterizing the molecular weight. • The thermo-oxidative degradation of PBAT was studied by LF-NMR. • The error between the method used by LF-NMR and the actual test is less than 10%. [ABSTRACT FROM AUTHOR]

Shale reservoirs are rich in micro and nanoscale pores and fractures, resulting in a very complex interaction mechanism between oil and water. In this paper, firstly, the differences in fluid enrichment mechanisms and evolution model characteristics within multi-level pore networks are revealed. Secondly, a linkage mechanism model of "relaxation time - multistage pore structure - fluid evolution" is constructed. Thirdly, the interaction mechanism of the coupling of mineral types, multiphase fluid evolution, and pore-fracture networks is clarified. Results show that: (a) For the 4 shale samples, the distribution of p 1 peak is less than 1 ms, p 2 peak is between 1 ms and 20 ms, and p 3 peak is greater than 20 ms. (b). The distribution of p 1, p 2, and p 3 peaks in the T 2 spectrum of saturated oil from different shale samples is different. (c) For a typical sample, the total porosity of saturated water in the felsic shale in Research Area 1 is 6.73%; the total porosity of saturated oil is 4.15%. • The differences in fluid enrichment mechanisms and evolution model characteristics are revealed; • A coupled model of "relaxation time - multistage pore structure - fluid evolution" is constructed; • The mechanism of coupling of mineral types, fluid evolution, and pore-fracture networks is clarified. [ABSTRACT FROM AUTHOR]

Abstract In this work, high-alcoholysis polyvinyl alcohol (PVA) films with sorbitol as plasticizer are obtained through the melt processing and characterized with low field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC) etc. to investigate the water mobility, state and distribution as well as its effect on the performance of the films. The results show that two state of water, e.g. bound water and free water, exist and sorbitol can effectively bind w'ater in PVA films. The sorbitol molecules can effectively promote the formation of bound water. Therefore, with the increase of sorbitol plasticizer, the bound water content increases. The water migration study indicates that sorbitol can form strong hydrogen bonds with water and make the bound water more stable. The tensile strength and the haze of the films increase with increased bound water content. Graphical abstract Brief schematic of paper. Image 1 Highlights • LF-NMR investigates water state. • Change state of water. • Retain the bound water in PVA. • Bound water increases haze. • The bound water increases. [ABSTRACT FROM AUTHOR]

Instant sea cucumber has become one popular product due to its convenience to eat, favourable taste and minimal loss of nutrients and bioactive components. However, there was rare information about the water dynamic of instant sea cucumber subjected to multiple freeze-thaw cycles. In this study, low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance image (MRI) were employed to investigate the effect of freeze-thaw cycles on water status of instant sea cucumber. Four water populations corresponding to strongly bound water, weakly bound water, immobile water and free water were observed in instant sea cucumber. With the increase of freeze-thaw cycles, the transverse relaxation time of immobile and free water increased, while the peak area of free water decreased significantly. MRI enabled the visualization of water migration of instant sea cucumber during multiple freeze-thaw cycles. Multiple freeze-thaw cycles also led to significant changes of other quality properties including thawing loss, WHC, color parameters, texture and protein content, and enlarge the interspace between fiber network in microstructure. Good correlations between T 22 , A 22 , A 23 and thaw loss, WHC, L *, hardness and collagen content (0.873 ≤ r ≤ 0.958) revealed LF-NMR may be an effective real-time monitoring method of these physicochemical parameters as a non-destructive technique. [ABSTRACT FROM AUTHOR]

The aim of this study was to verify the influence of selected phosphate salts (sodium diphosphate and trisodium phosphate) on the gelling properties and water state of whole egg gel. As shown by the results, the gel and water holding properties of whole egg was effectively improved after the addition of sodium diphosphate and trisodium phosphate, possibly through affecting the solubility, surface hydrophobicity, z-average particle size and pH of liquid egg dispersions. The difference in the viscoelastic properties of whole egg gels brought by two phosphate salts was related to their obvious difference in calculated ionic strength and pH. As the addition level of phosphate salts increased, the protein secondary structure after gelation was changed remarkably, characterized by the decrease of α-helix content and the increase of β-sheet content. The gel β-sheet content was positively correlated with fracture strain and percentage of bound water and immobilized water, while the α-helix content was negatively correlated with fracture strength. The scanning electron microscope (SEM) results showed that the addition of phosphate salts would facilitate the formation of a fine high strength stranded structure. Moreover, the color characteristics of whole egg gels can be more effectively improved by sodium diphosphate in comparison with trisodium phosphate. [ABSTRACT FROM AUTHOR]

The effects of NaCl addition on the gelling and water holding properties of egg white/yolk gels were studied via solubility, surface hydrophobicity, reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared spectra (FTIR), textural analysis, low-field nuclear magnetic resonance (LF-NMR) and centrifugation. Results showed that more solubility and surface hydrophobicity increase of egg yolk dispersions were observed than that of egg white dispersions. SDS-PAGE results indicated that the different change trend of surface hydrophobicity between two egg proteins was closely related with the dissociation of egg yolk granule proteins. NaCl-induced protein heat denaturation will result in the decrease of ordered secondary structure (α-helix and β-sheet) by breaking hydrogen bond for both egg protein gels. A rapid decrease ( p < 0.05) in fracture strength/strain of egg white gels was found as the NaCl increased, while the fracture strength/strain of egg yolk gels first rose and then descended, indicating that the significant increases of solubility and hydrophobicity of egg yolk dispersions at a certain NaCl concentration (≤1.8%) were benefit to the formation of strong molecule interaction among gel network. Results from LF-NMR and centrifugation water holding capacity (WHC) tests revealed that NaCl addition affected the WHC of egg white gels by increasing the mobility and distribution of free water, and had a complex influence on proton mobility and relaxation peak changeability of egg yolk gels due to the interaction among lipid, protein and water. [ABSTRACT FROM AUTHOR]

In this study, a recently developed methodology to assess aging of pavements by using Low Field Nuclear Magnetic Resonance (LF-NMR) was applied to asphalt mix samples at different aging states. The ultimate objective of this method is to monitor the long-term aging of asphalt binder in mixture cores without binder extraction. The asphalt samples were long-term aged at 70 °C for different durations. At the end of this process, specimens were heated again to 70 °C and measured in the LF-NMR while cooling to room temperature. Lower cumulative amplitudes were found in samples that were aged for longer durations. An NMR probe that can detect shorter transverse relaxation times T 2 was used in order to increase the accuracy of the method. The unaged asphalt binder was measured as temperature dropped from 80 to 40 °C and it was observed that the cumulative amplitude was fairly constant throughout the process. The corresponding change in the binder viscosity was expressed by the T 2 shifts to shorter times. This means that the faster NMR probe was capable to minimize the NMR signal losses and therefore it is a suitable tool to investigate asphalt samples. Asphalt binders were extracted from the aged samples and subjected to LF-NMR measurements with the fast NMR probe. It was possible to detect aging trends in the binders, which were in agreement with viscosity trends measured with the Dynamic Shear Rheometer (DSR). The differences in the cumulative amplitude among binders with different aging states mainly depend on the hydrogen nuclei to weight ratio (chemistry) and less on the temperature and measurable limit of the NMR device. This improves the accuracy of the method in the estimation of the binder aging state. In addition, the employed aggregates were separately investigated using LF-NMR. [ABSTRACT FROM AUTHOR]

• The temperature characteristics along the muddy clay column are analyzed with moisture migration. • Moisture migration along large column during F-T process is discussed by NMR scanning results. • Pore size distribution along muddy clay column during F-T process is determined. • The coupling mechanism between moisture migration, temperature, and pore structure of clay is inferred. Nowadays, artificial ground freezing (AGF) is widely used in the construction of underground spaces in soft soil areas. Most of the existing studies are focused on micro and macro analyses of small volume samples under AGF, while the research on large soil column is insufficient. Therefore, it's crucial to explore the characteristics of the large soil column by AGF. In this paper, the low field nuclear magnetic resonance (LF NMR), and the unidirectional freezing test of large muddy clay columns were carried out. The results indicate that the most difference is that along the soil column, each soil layer has a connection with each other, owing to the pore structure connectivity and moisture migration within it. Moreover, slow-growing platforms or even temperature crosses appeared during thawing, due to the downward movement of water under consolidation and gravity which may interfere with heat transfer (upward movement). Along the large muddy clay column, moisture migration in the soil column is coupled with temperature as well as pore structure. Specifically, temperature difference and pore structure provide the power source and transport channel for moisture migration, respectively, while the moisture migration changes the temperature of each layer of the soil column and the composition of the pore structure. The pore structure indirectly influences the temperature of soil column by affecting the amount of moisture migration, while temperature significantly changes the number and size of pores inside the soil column. Furthermore, by LF NMR experiments, it was found that the pore size distribution was relatively dispersed and the characteristics of moisture migration at different heights of the soil column could be divided into three stages. This study can be used as theoretical guidance for understanding the change laws among moisture migration, temperature, and pore structure of the muddy clay as well as for helping the construction of AGF in the underground space. [ABSTRACT FROM AUTHOR]

Kiwifruit undergoes rapid quality changes after harvest, which has an important influence on quality grading and processing. The effects of postharvest ripening on water status, distribution, drying characteristics, and the effects of ripening and drying on volatile profiles, phytochemical contents, antioxidant capacity, and microstructure of kiwifruit were investigated. During postharvest storage, the water binding ability decreased, the water distribution, migration path, and the microstructure changed, which led to the shortening of drying time first and then prolongation. Ripeness affected kiwifruit's volatile composition, phytochemical composition and antioxidant capacity, and the drying process after storage reduced the differences of nutrients and volatile components caused by different postharvest ripeness. The findings in current work provide practical implications for the quality classification and effective drying of kiwifruit during post-harvest ripening. • Postharvest ripening affected physicochemical properties and drying characteristics. • Changes in water binding state and microstructure led to differences in drying rate. • Ripeness of kiwifruit affected the heat transfer during drying process. • Both postharvest ripening and drying significantly affected the volatile profiles. • Storage and drying progress affected phytochemical and antioxidant activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The detection of salted sea cucumber was realized by near infrared hyperspectral imaging and low field nuclear magnetic resonance. • Cuckoo optimization algorithm was proved to be effective in extracting salient features from the data, which was helpful to improve the accuracy of the models. • Deep learning framework was used to establish moisture content prediction models of salted sea cucumber based on single-data and multiple-data. The accurate control of moisture content (MC) during the processing of sea cucumber is beneficial to improve the taste of sea cucumber and maintain its nutritional value, which is directly related to the quality and shelf life of sea cucumber. The purpose of this study is to explore the feasibility using deep learning (DL) to realize rapid nondestructive detection of MC in salted sea cucumbers based on hyperspectral imaging (HSI) and low field nuclear magnetic resonance (LF-NMR) data. Firstly, three Cuckoo Search (CS) dimensionality reduction algorithms (Traditional-CS, Binary-CS and Chaotic-CS) were combined with DL framework respectively using HSI and LF-NMR data to establish prediction models, which proved the feasibility of DL framework in predicting the MC of sea cucumbers, and Chaotic-CS algorithm was selected as the optimal dimensionality reduction algorithm. Then, the MC visualization based on HSI and LF-NMR data was realized respectively to detect the migration and decrease of MC. Finally, using both HSI and LF-NMR data, the advantages of the models based on Fusion-net DL (FDL) framework were discussed, which showed better performance than the single-data models, with R C 2 of 0.9929, RMSE C of 0.0016, R P 2 of 0.9936 and RPD of 12.5041. In summary, the rapid nondestructive detection of MC in salted sea cucumbers could be realized by HSI and LF-NMR data based on DL framework, and the advantage of data fusion detection based on FDL framework was verified. [ABSTRACT FROM AUTHOR]

Fermentation, as a simple, safe and environmentally friendly technology, is promising in the modification of proteins. In this study, the liquid whole egg (LWE) was fermented at 37 °C by Lactiplantibacillus plantarum 90 (L. plantarum 90) which the dose of inoculation was about 8 Log 10 CFU mL−1. During the process, the total aerobic mesophilic count (TAM) and the number of lactic acid bacteria (LAB) of LWE increased at 3 h and then decreased, consistent with the changes in protein solubility. Besides, the T 2 relaxation time of fermented egg gels moved to low relaxation time (T 22 shifted from 2154.44 ms (0 h) to 1232.85 ms (9 h)), indicating that the water retention of fermented egg gels was enhanced. After fermentation, it could be seen intuitively that the porous structure of the gel surface almost disappeared, along with the improved springiness and brightness by texture and color measurement. This study suggested that moderate fermentation (L. plantarum 90, 1% v /v, 9 h) could effectively improve the gel property of LWE, and thus had a potential to expand the application of LWE in the food industry. • Lactiplantibacillus plantarum fermentation promoted the formation of soft liquid whole egg (LWE) gels. • The springiness of LWE gels was enhanced due to the reduced pores after fermentation. • Increased β-sheet formation was beneficial to the production of low-water mobility LWE gels. [ABSTRACT FROM AUTHOR]

The study of bone morphology is of great importance as bone morphology is influenced by factors such as age and underlying comorbidities and is associated with bone mechanical properties and fracture risk. Standard diagnostic techniques used in bone disease, such as Dual-Energy X-ray absorptiometry and ultrasonography do not provide qualitative and quantitative morphological information. In recent years, techniques such as High Resolution Computed Tomography (HR-CT), micro- CT, Magnetic Resonance Imaging (MRI), and Low Field Nuclear Magnetic Resonance (LF-NMR) have been developed for the study of bone structure and porosity. Data obtained from these techniques have been used to construct models to predict bone mechanical properties thanks to finite element analysis. Cortical porosity has been extensively studied and successfully correlated with disease progression and mechanical properties. Trabecular porosity and pore size distribution, however, have increasingly been taken into consideration to obtain a comprehensive analysis of bone pathology and mechanic. Therefore, we have decided to evaluate the ability of micro- CT (chosen for its high spatial resolving power) and LF-NMR (chosen to analyze the behavior of water molecules within trabecular bone pores) to characterize the morphology of trabecular bone in osteoporosis. Trabecular bone samples from human femoral heads collected during hip replacement surgery were from osteoporosis (test group) and osteoarthritis (control group) patients. Our data show that both micro- CT and LF-NMR can detect qualitative changes in trabecular bone (i.e., transition from plate-like to rod-like morphology). Micro- CT failed to detect significant differences in trabecular bone morphology parameters between osteoporotic and osteoarthritic specimens, with the exception of Trabecular Number and Connectivity Density, which are markers of osteoporosis progression. In contrast, LF-NMR was able to detect significant differences in porosity and pore size of trabecular bone from osteoporotic versus osteoarthritic (control) samples. However, only the combination of these two techniques allowed the detection of structural morphometric changes (increase in the larger pore fraction and enlargement of the larger pores) in the trabecular bone of osteoporotic specimens compared to osteoarthritic ones. In conclusion, the combined use of LF-NMR and micro- CT provides a valuable tool for characterizing the morphology of trabecular bone and may offer the possibility for a new approach to the study and modeling of bone mechanics in the context of aging and disease. [Display omitted] • Aging and disease lead to changes in bone morphometric parameters such porosity. • Bone porosity affects mechanical properties and risk fracture in aging and diseases. • Low field nuclear magnetic resonance (LF-NMR) is highly sensitive to bone porosity. • LF-NMR and microcomputed tomography can finely characterize bone morphology. [ABSTRACT FROM AUTHOR]

• Low field NMR was firstly used to directly monitoring the pore structure changes. • A mathematical model combined T 2 with protein adsorption capacity Q was established. • Adsorption mechanisms between agarose and dextran-grafted agarose media were found. • Dextran-grafted agarose can form multilayer adsorption and have high contact area. The adsorption process of bovine serum albumin (BSA), ovalbumin (OVA) and human immunoglobulin G (IgG) on agarose ion-exchange media Q Sepharose FF and two dextran-grafted agarose media including Q Sepharose XL and Capto Q were studied using low field nuclear magnetic resonance (NMR). The T 2 relaxation time was found directly proportional to the pore size and diminished after protein adsorbed, therefore, a theoretical model describing the relationship between protein binding amount and T 2 relaxation signals was established. The model parameters, a, which reflects the contact area between the adsorbed protein and media surface, and the δ , which defined as the ratio of the protein volume to the pore volume after adsorption, were found to describe the pore occupation states of proteins in media with different pore structures very well. For small proteins, such as BSA and OVA, monolayer adsorption occurred on Q Sepharose FF, which has no dextran chains. Therefore, the adsorbed protein only occupied 49.05% of the pore volume for BSA and 25.51% for OVA, and contact area of each protein on the media were also low, suggesting mostly monolayer adsorption occurred. In the contrast, their adsorption to Q Sepharose XL and Capto Q with dextran chains tended to form multilayer adsorption, thus higher contact area was obtained and the pore volumes were almost 100% occupied. For large protein, such as IgG, the adsorption to all these three media was similar and about 30% of the pore volume were occupied, probably due to the similar restriction for IgG to entering the media pore. Results of this study will help to elucidate the relationship between protein adsorption and pore size variation, which present the significance of low field NMR in understanding protein adsorption mechanism. [ABSTRACT FROM AUTHOR]