Surface Of Beads Research Articles

In-situ study on the heterocoagulation between fine coal particles and coarse glass beads by the particle vision and measurement (PVM) techniques

Heterocoagulation between mineral particles is an important phenomenon in mineral processing. Although various characterization methods have been available for characterizing heterocoagulation, in-situ characterization techniques are still lacking. In the present work, a novel in-situ particle vision and measurement (PVM) system was developed to investigate heterocoagulation between coarse and fine particles, which is consistent with the common situation of mineral processing. The heterocoagulation between fine coal particles and coarse glass beads was observed at different pH values and stirring speeds. It was found that the heterocoagulation degree decreased with the increase of pH, which is consistent with the DLVO theoretical calculation results. The heterocoagulation degree decreased with the increase of stirring speed. This indicated that heterocoagulation can be inhibited by high intensity conditioning. Moreover, it was observed that the coated coal particles were not randomly distributed on the glass bead surface. Under certain hydrodynamic conditions, the coal particles were even more distributed at the rear of the glass bead. It is concluded that the microhydrodynamics has a significant effect on the collision frequency and heterocoagulation.

Pd@HKUST-1@Cu(II)/CMC composite bead as an efficient synergistic bimetallic catalyst for Sonogashira cross-coupling reactions

We fabricated an efficient Pd@HKUST-1@Cu(II)/CMC composite bead catalyst through an innovative strategy based on the unique properties of metal-organic frameworks (MOFs) and carboxymethylcellulose (CMC). In this strategy, HKUST-1 MOFs were grown in-situ on the surface of micrometer-sized Cu-based CMC beads (Cu(II)/CMC), then Pd(II) ions were incorporated into the pores of the MOF and further be partially reduced to Pd(0) NPs, which is an active species for oxidative addition with aryl halides in Sonogashira reactions. The micron-sized Cu(II)/CMC beads were formed through inter/intramolecularly crosslinking facilitated by Cu(II) ions, which was achieved by the metathesis of Cu(II) with numerous carboxylic groups of CMC. Such Cu(II)/CMC bead offers many Cu(II) ions as interaction sites for in-situ nucleation and growth of HKUST-1 MOFs. The architecture and composition of the prepared Pd@HKUST-1@Cu(II)/CMC composite were fully verified by various techniques such as FTIR, XRD, TGA, BET, XPS, SEM, TEM, EDX, and elemental mapping analysis. This novel composite bead was applied as an efficient and reusable heterogeneous Pd/Cu bimetallic catalyst for Sonogashira reactions, decarbonylative Sonogashira reaction, and Sonogashira cyclization tandem reactions. The catalyst is readily isolated by simple filtration, and can be reused for five consecutive runs with retaining its activity and structural integrity.

Aptamer-functionalized polydiacetylene biosensor for the detection of three foodborne pathogens.

Rapid, simple and sensitive screening of foodborne pathogens is of great significance to ensure food safety. In this study, an aptamer-functionalized polydiacetylene (Apta-PDA) biosensor was developed for the detection of E. coli O157:H7, S. typhimurium or V. parahaemolyticus. First, aptamers responding to the target bacteria were modified on the surface of magnetic beads by covalent binding to form MBs-oligonucleotide conjugates for bacterial enrichment. Then, an Apta-PDA biosensor was obtained by connecting the aptamers to the PDA nanovesicles using the carbodiimide method. Molecular recognition occurred in the presence of the target bacteria, whereby the aptamer folded into a sequence-defined unique structure, resulting in an MBs-Apta/bacteria/Apta-PDA sandwich structure. Due to the optical properties of PDA, the blue-red transition of the detection system could be observed by the naked eye and quantified by the colorimetric response percentage (CR%). Under optimized conditions, the detection limits of E. coli O157:H7, S. typhimurium and V. parahaemolyticus were 39, 60 and 60CFU/ml, respectively, with a selectivity of 100% and a reaction time of 30min. Compared with the gold standard method, the accuracy of the three target bacteria detection reached 98%, 97.5% and 97%, respectively, and the sensitivity and specificity were both greater than 90%. The entire detection process was rapid and easy to execute without any special equipment, making this technology particularly suitable for resource-poor laboratories or regions.

B-087 The Antifouling Properties of BSA on Magnetic Beads are Affected by BSA Grade, Bead Type, and pH

Abstract Background BSA (bovine serum albumin) is a protein that is widely used for its antifouling properties in a variety of immunoassays. One such immunoassay is a bead-based ELISA (enzyme-linked immunosorbent assay), which can provide quantitative detection of many diverse analytes. BSA increases the sensitivity of a bead-based ELISA by coating the beads and blocking nonspecific interactions, thereby lowering background noise. However, the BSA grade chosen for the assay is frequently based on experience, as there is a lack of understanding of how BSA grades interact with different bead surfaces under various assay conditions. The objective of this study is to examine if different BSA grades work better with particular bead chemistries and how pH influences those interactions. Specifically, the aim is to quantify the amount of BSA on ELISA beads and assess the blocking of nonspecific antibody signal with different bead types, BSA grades, and pH. Methods The mass of BSA binding to beads was measured by heating BSA-coated beads in 1x SDS loading dye, then running on a denaturing PAGE gel. Total protein was measured by densitometry against a standard curve using ImageJ. The amount of blocking was measured using a modified bead-based ELISA, comparing the amount of antibody-HRP binding to the beads in the presence and absence of BSA. The amount of antibody-HRP was measured using a SpectraMax Plus 384 plate reader against a standard curve. All data were analyzed using GraphPad Prism and presented as the average of at least three independent replicates with error bars representing standard deviation. Conditions tested include different Dynabeads (hydrophilic vs. hydrophobic - Dynabeads M-270 Carboxylic Acid and M-280 Tosylactivated), BSA grade (fatty acid (FA) vs. fatty acid-free (FAF) - Proliant SKUs 68100 and 68700), and pH (7 vs. 5.2). Results The choice of pH is more influential than the BSA grade on bead surface coating and blocking, regardless of bead type. Lowering the pH from 7 to 5.2 increases the mass of BSA on the beads ∼1.7-fold for hydrophobic beads and ∼10-fold for hydrophilic beads. However, the mass of BSA on the beads is reduced after the pH returns to 7, indicating the increased BSA binding at pH 5.2 is reversible. We also observed BSA decreases nonspecific antibody-bead interactions by up to 90%, depending on assay conditions. Though the amount of BSA coating the beads between FA and FAF grade BSA is not significant, FAF grade BSA blocks the antibody-bead interactions ∼10% more than FA grade BSA, suggesting FAF grade BSA has better antifouling properties. Conclusion Herein, we show the presence of BSA reduces the noise within bead-based ELISAs by binding to the bead and blocking nonspecific antibody-bead interactions, regardless of BSA grade, bead type, and pH. FAF grade BSA demonstrates slightly better blocking than FA grade BSA, but both BSA grades decreased nonspecific antibody-bead interactions. Further, BSA shows antifouling properties at the typical assay pH of 7, but lowering the pH to 5.2 can significantly increase BSA bead coating.

B-259 Exocas-2 Rapid and Pure Isolation of Exosomes by Anionic Exchange using Magnetic Beads

Abstract Background Extracellular vesicles (EVs) are considered essential biomarkers in liquid biopsies. Despite intensive efforts aimed at employing EVs in a clinical setting, workable approaches are currently limited owing to the fact that EV-isolation technologies are still in a nascent stage. This study introduces a magnetic bead-based ion exchange platform for isolating EVs called ExoCAS-2 (exosome clustering and scattering). Owing to their negative charge, exosomes can easily adhere to magnetic beads coated with a polycationic polymer. Owing to the features of magnetic beads, exosomes can be easily processed via washing and elution steps and isolated with high purity and yield within 40 min. Methods Cationic salt is coated on the surface of magnetic beads with carboxyl group surface residues. Inject the cation coated magnetic bead (ExoCAS) into the plasma solution and incubate in 4°C for 30 minutes. By charge interaction, negative charged EVs are attached to the cationic beads. And then, pH 6 washing buffer and 1M NaCl elution buffer were used for EV isolation. Results The present results confirmed the isolation of exosomes through analyses of size distribution, morphology, surface and internal protein markers, and exosomal RNA. Compared with the commercially available methods, the proposed method showed superior performance in terms of key aspects, including operation time, purity, and recovery rate. Conclusion This highlights the potential of this magnetic bead-based ion exchange platform for isolating exosomes present in blood plasma.

First biosensing platform for detecting traces of almonds in processed foods by electrochemical determination of the allergenic protein Pru du 6

A novel electrochemical bioplatform for Pru du 6determination, one of the most abundant and allergenic almond proteins, was developed to detect traces of almonds in processed foods. The bioplatform combines the application of a sandwich immunoassay on the surface of magnetic beads using specific antibodies unmodified or conjugated to horseradish peroxidase as capture and detection antibodies. The resulting magnetic bioconjugates are trapped on the surface of disposable carbon electrodes, and amperometry in the presence of hydrogen peroxide and hydroquinone is employed to measure the change in the cathodic current, which is proportional to Pru du 6 concentration. The developed bioplatform exhibited good selectivity and sensitivity, offering a detection limit of 0.12 ng mL−1 of Pru du 6. It could determine Pru du 6 in raw dough and baked cookies incurred with 0.2 µg g−1 of almond protein with acceptable precision, providing results comparable to those obtained using an ELISA technique.

Oriented display of cello-oligosaccharides for pull-down binding assays to distinguish binding preferences of glycan binding proteins

The production of biofuels from lignocellulosic biomass using carbohydrate-active enzymes like cellulases is key to a sustainable energy production. Understanding the adsorption mechanism of cellulases and associated binding domain proteins down to the molecular level details will help in the rational design of improved cellulases. In nature, carbohydrate-binding modules (CBMs) from families 17 and 28 often appear in tandem appended to the C-terminus of several endocellulases. Both CBMs are known to bind to the amorphous regions of cellulose non-competitively and show similar binding affinity towards soluble cello-oligosaccharides. Based on the available crystal structures, these CBMs may display a uni-directional binding preference towards cello-oligosaccharides (based on how the oligosaccharide was bound within the CBM binding cleft). However, molecular dynamics (MD) simulations have indicated no such clear preference. Considering that most soluble oligosaccharides are not always an ideal substrate surrogate to study the binding of CBMs to the native cell wall or cell surface displayed glycans, it is critical to use alternative reagents or substrates. To better understand the binding of type B CBMs towards smaller cello-oligosaccharides, we have developed a simple solid-state depletion or pull-down binding assay. Here, we specifically orient azido-labeled carbohydrates from the reducing end to alkyne-labeled micron-sized bead surfaces, using click chemistry, to mimic insoluble cell wall surface-displayed glycans. Our results reveal that both family 17 and 28 CBMs displayed a similar binding affinity towards cellohexaose-modified beads, but not cellopentaose-modified beads, which helps rationalize previously reported crystal structure and MD data. This may indicate a preferred uni-directional binding of specific CBMs and could explain their co-evolution as tandem constructs appended to endocellulases to increase amorphous cellulose substrate targeting efficiency. Overall, our proposed workflow can be easily translated to measure the affinity of glycan-binding proteins to click-chemistry based immobilized surface-displayed carbohydrates or antigens.

A CRISPR/Cas12a-SERS platform for amplification-free detection of African swine fever virus genes

A surface-enhanced Raman scattering (SERS) strategy combined with a CRISPR/Cas12a system is designed for the amplification-free gene detection of African swine fever virus (ASFV). A SERS sensing probe was fabricated by conjugating plasmonic SERS tags on the magnetic bead (MB) surface with an single-stranded DNA (ssDNA) as a linker. The target ASFV gene-activated Cas12a protein starts the trans-cleavage function on the linker ssDNA, which causes the release of SERS tags, leading to a decrease of the SERS signal detected above the collective MBs. Two signal enhancement strategies were adopted to improve the liquid-phase detection sensitivity arriving at the fM level. One is the unlimited trans-cleavage function of the Cas12a protein, and the other is the magnetic-induced collection of probes that can significantly gather the analytes from the solution to the laser spot and provide SERS hotspots during SERS measurement. Detection range is from 100 nM to 10 fM without the gene amplification steps. This sensing method achieved the SERS detection of ASFV gene in the serum system and the extracted nucleic acids in viral samples with high sensitivity and selectivity at a relative standard deviation of <8%. This sensing platform is mainly in use for site inspection and quick testing of gene samples.

Ultra-sensitive electrochemiluminescent biosensor for miRNA based on CRISPR/Cas13a trans-cleavage-triggered hybridization chain reaction and magnetic-assisted enrichment.

The great selectivity and trans-cleavage activity of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a had been coupled with high amplification efficiency of hybridization chain reaction (HCR) and magnetic-assisted enrichment, high sensitivity of electrochemiluminescence (ECL) detection to develop an ultra-sensitive biosensor for microRNA-21 (miRNA-21). The CRISPR/Cas13a was used to recognize target RNA with high specificity and performed the trans-cleavage activity. An initiation strand was generated to bind to the probe on the surface of nanomagnetic beads and then trigged HCR to produce long double-strand DNAs (dsDNAs) to realize signal amplification. Ru(phen)32+ can be inserted in the groove of the dsDNAs and acts as the ECL indicator, which can be separated through magnetic enrichment and allowed the platform to reduce thesignal background. Under the optimized conditions, there is a good linear correlation between the ECL intensity and the logarithm of miRNA-21 concentration in the range 1 fM-10nM; the limit of detection (LOD) was 0.53 fM. The proposed system was applied to detect miRNA-21 from the urine of acute kidney injury (AKI) patients with goodresults.

Lab‐in‐a‐Bead: Magnetic Janus Bead Probe for the Detection of Biomarkers in Blood

AbstractRemotely handled miniaturized colorimetric sensor platforms with multiple functionalities are able to mimic conventional laboratory operations with reduced assets. The integration of a magnetic phase in a miniaturized hydrogel sensor system allows the manipulation of the sensor, under a magnetic field, in a programmable manner. However, dark color interferences from conventional magnetic phases (Fe3O4, Fe2O3, and Fe micro/nanoparticles) affect the signal readout, hindering the colorimetric response. Therefore, a novel Janus bead configuration is introduced and tested by the localized incorporation of ferromagnetic iron microparticles into a TiO2 nanotubes/alginate hydrogel bead biosystem, under an applied magnetic field. The so‐called hydrogel Janus bead shows both, magnetic translocation and biosensing properties in the same bead. These beads are used for the direct colorimetric analysis of biomarkers in blood. The surface of the Janus bead prevents the biofouling of red blood cells, keeping the sensor surface clean for accurate optical colorimetric analysis. Moreover, the external magnetic manipulation of the bead permits precise control of the time and position of the bead in the sample. Therefore, multiple functionalities are presented by a single magnetic TiO2 nanotubes/alginate Janus bead such as actuation, low biofouling, and sensing, positioning this technology as a truly Lab‐in‐a‐Bead System.

SERS sensor combined with the dual DNA cycling amplification assay for the sensitive detection of antibiotic resistance gene in environmental samples

Antibiotic resistance genes (ARGs) have emerged as new environmental pollutants, and even minute quantities of them can seriously affect the environment. Thus, it is urgently required to test trace ARGs. Herein, a surface-enhanced Raman scattering (SERS) sensor based on the dual cycling amplification has been developed for the ultrasensitive detection of bla-TEM. First, the capture DNA on the surface of magnetic beads and the Hg2+ aptamer-based capture strand could achieve the capture, separation, and enrichment of the bla-TEM from the relatively complex samples. Then, the dual amplification process was finished under the catalysis of the enzymes, and the entire process was operated in one step under the isothermal condition. Finally, the enriched SERS nanoprobes were obtained via the feasible magnetic separation and provided Raman signals for the detected bla-TEM under the laser irradiation. Under the optimum experimental conditions, the sensor exhibited excellent sensitivity and good selectivity, obtaining a linear range of 0.1 zM-300 aM and a limit of detection (LOD) of 0.02 zM. It can be successfully used to measure bla-TEM in actual environmental samples, which was in good accordance with the conventional polymerase chain reaction (PCR) analysis, showing great promise for detecting trace ARGs in the environmental samples.

Partially Bio‐Based Polyester Bead Foams via Extrusion Foaming of Poly(butylene terephthalate)/Poly(butylene furanoate) Blends

AbstractThe interest in bio‐based alternatives to classical polyesters such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) is steadily growing to achieve a more sustainable approach to polymer materials. In this study, PBT/poly(butylene furanoate) (PBF) blends are prepared, characterized and extrusion foamed. PBF as a bio‐based polyester offers two advantages. The ecological footprint of the material is reduced, and additionally, it can be used in Diels‐Alder reactions at the blend surface to support fusion of the foamed beads. The blending behavior of the polyesters is investigated using samples prepared in a microcompounder, particularly focused on the miscibility of the blends and transesterification reactions. The blends are thermodynamically immiscible but show a certain degree of transesterification according to nuclear magnetic resonance (NMR) spectroscopy. The morphology of blend beads produced by an extrusion foaming process is analyzed regarding their cell density, cell size distribution, and open‐cell content. It is shown that PBF has a positive effect on the bead foam morphology. The use of a bifunctional linker designed for chemical fusion of the bead surfaces allows to obtaining of molded parts, in contrast to beads containing pure PBT.

Construction of a dual-signal sensing platform based on DNA enhanced peroxidase-activity of iron cobalt oxide nanosheets for thrombin detection

Thrombin played important roles for the diagnosis of neurodegenerative and cardiovascular diseases. Herein, we successfully constructed a rapid and sensitive fluorescence and colorimetric dual-signal sensing strategy for the detection of thrombin by taking advantage of the DNA-enhanced peroxidase like activity FeCo-ONSs and magnetic separation. In this work, single-stranded DNA S1 with thrombin aptamer was used to enhance the catalytic activity of FeCo-ONSs, and single-stranded DNA S2 with different thrombin aptamer was modified on the surface of magnetic beads (MBs) to construct MBs-S2 for subsequent magnetic separation. In the presence of thrombin, S1 and MBs-S2 quickly combined with thrombin and the amount of S1 decreased in the solution after magnetic separation. The enhancement of peroxidase like activity of S1/FeCo-ONSs was weakened, resulting in the inhibition of the catalytic oxidation process of substrate TMB. The formation of oxTMB and the fluorescence quenching efficiency of MoS2 QDs were further affected. Therefore, the quantitative detection of thrombin can be achieved by measuring the absorption signal of oxTMB and the fluorescence signal of MoS2 QDs. The limits of detection for thrombin were 0.67 pM and 2.36 pM by the outputting fluorometric and colorimetric dual signals, respectively. This sensing strategy not only has high specificity, but also can be expanded as a more universal platform for sensitive detection of different proteins by changing the aptamer probe pairs.

Dual-probe ligation without PCR for fluorescent sandwich assay of EGFR nucleotide variants in magnetic gene capture platform.

A simple, rapid, and highly efficient fluorescent detection technique without PCR through dual-probe ligation with the genetic capture of magnetic beads and reported probe was developed for determination of epidermal growth factor receptor (EGFR) gene exon 19 deletions. The EGFR exon 19 deletion mutation makes up 48% of all mutations associated with anti-tyrosine kinase inhibition sensitivity, and thus, the EGFR nucleotide variant isvery important in clinical diagnosis. In this approach, the dual-probe ligation was designed to target exon 19 deletion. The magnetic genetic captured system was then applied to capture the successful dual-probe ligation. Thereafter, a reporter probe which is coupled with 6-fluorescein amidite (6-FAM) was introduced to hybridize with dual-probe ligation product on the surface of streptavidin magnetic beads, and finally, the supernatant was taken for fluorescence measurements for distinguishing mutant types from wild types. After optimization (the RSD of the fluorescent intensity was less than 4.5% (n = 3) under the optimal condition), 20 blind DNA samples from the population were analyzed by this technique and further confirmed by direct sequencing. The results of our assay matched to those from direct sequencing data, evidencing that the developedmethod is accurate and successful. These 20 blind DNA samples were diagnosed as wild and then spiked withdifferent percentages of the mutant gene to quantify the ratio of the wild and mutant genes. This strategy was also successfully applied to quantify the ratio of the wild and mutant genes with good linearity at the λex/λem of 480 nm/520 nm (r = 0.996), and the limit of detection reached 1.0% mutant type. This simple fluorescent detection of nucleotide variants shows its potential to be considered a tool in biological and clinical diagnosis. Importantly, this strategy offers a universal detection capability for any kind of mutation (point, deletion, insertion, or substitution) in a gene of interest.

Isolation and Detection of Exosomal Mir210 Using Carbon Nanomaterial-Coated Magnetic Beads.

MicroRNAs (miRNAs) are short non-coding RNAs that are found in various cellular compartments and play an important role in regulating gene expression. Extracellular miRNAs, such as those found within extracellular vesicles such as exosomes are involved in cell-to-cell communication. The intercellular transfer of miRNAs has been implicated in various diseases' pathogenesis including cancer and has been studied extensively as potential cancer biomarkers. However, the extraction of miRNA from exosomes is still a challenging task. The current nucleic acid extraction assays are expensive and labor-intensive. In this study, we demonstrated a microfluidic device for aptamer-based magnetic separation of the exosomes and subsequent detection of the miRNA using a fluorescence switching assay, which was enabled by carbon nanomaterials coated on magnetic beads. In the OFF state, the fluorophore-labelled cDNA is quenched using carbon nanomaterials. However, when the target miRNA210 is introduced, the cDNA detaches from the bead's surface, which leads to an increase in the fluorescence intensity (ON state). This increment was found to be proportional to miRNA concentration within the dynamic range of 0-100 nM with a detection limit of 5 pM. The assay was validated with spiked miRNA using the standard RT-PCR method. No notable cross-reactivity with other closely related miRNAs was observed. The developed method can be utilized for the minimally invasive detection of cancer biomarkers.

Dual-Toehold-Probe-Mediated Exonuclease-III-Assisted Signal Recycles Integrated with CHA for Detection of mecA Gene Using a Personal Glucose Meter in Skin and Soft Tissue Infection.

Staphylococcus aureus integrated with mecA gene, which codes for penicillin-binding protein 2a, is resistant to all penicillins and other beta-lactam antibiotics, resulting in poor treatment expectations in skin and soft tissue infections. The development of a simple, sensitive and portable biosensor for mecA gene analysis in S. aureus is urgently needed. Herein, we propose a dual-toehold-probe (sensing probe)-mediated exonuclease-III (Exo-III)-assisted signal recycling for portable detection of the mecA gene in S. aureus. When the target mecA gene is present, it hybridizes with the sensing probe, initiating Exo III-assisted dual signal recycles, which in turn release numerous "3" sequences. The released "3" sequences initiate catalytic hairpin amplification, resulting in the fixation of a sucrase-labeled H2 probe on the surface of magnetic beads (MBs). After magnet-based enrichment of an MB-H1-H2-sucrase complex and removal of a liquid supernatant containing free sucrase, the complex is then used to catalyze sucrose to glucose, which can be quantitatively detected by a personal glucose meter. With a limit of detection of 4.36 fM for mecA gene, the developed strategy exhibits high sensitivity. In addition, good selectivity and anti-interference capability were also attained with this method, making it promising for antibiotic tolerance analysis at the point-of-care.

A simple and sensitive turn-off biosensor for miRNA-21 detection based on tyramine signal amplification

The expression level of microRNA (miRNA) is strongly associated with a variety of diseases, and the development of new approaches for miRNA assay with high sensitivity will facilitate a deeper understanding of miRNA biological functions. Herein, a simple and sensitive turn-off biosensor for miRNA-21 detection based on tyramine signal amplification (TSA) was developed. In the absence of the target miRNA, the DNA capture probe on the surface of magnetic bead (MB) complementarily hybridizes with the DNA reporter probe; subsequently, a large amount of horseradish peroxidase (HRP) is bound by the biotin-streptavidin reaction; later, in the presence of hydrogen peroxide (H2O2), HRP catalyzes the deposition of biotinylated tyramine, and then the fluorescent phycoerythrin (PE) is successfully introduced via a biotin-streptavidin reaction, producing a robust fluorescence (FL) signal upon excitation. When the target miRNA is present, it competitively occupies the binding site of the DNA capture probes, leading to a decrease in the amount of the DNA reporter probes hybridized to the MB surface; subsequently, the effect of TSA is diminished, which ultimately leads to a weakened FL and generates the “turn-off” signal. This method utilizes the negative correlation between target miRNA concentration and FL intensity, which can achieve high sensitivity detection of miRNA with low detection limit. This method can be successfully applied to the determination of miRNA-21 in human lung cancer cells, which has great application potential for disease diagnosis.

Experimental and simulation study on the estimation of surface relaxivity of clay minerals

Nuclear Magnetic Resonance (NMR) is an important tool for the evaluation of pore structure and petrophysical properties of reservoir rocks. Pore Surface relaxivity (ρ2), which controls the relaxation decay due to the interaction between the spins and the pore surface, is an important parameter that impacts the interpretation of NMR for petrophysical properties. Sandstone rocks have complex minerology and consist of different clay minerals. Earlier efforts have reported the surface relaxivity of different rock types such as sandstone or carbonate, but less attention was given to the estimation of individual clay minerals surface relaxivity. The surface complexity and variable mineralogy (especially paramagnetic and ferromagnetic minerals) of clays can both impact the surface relaxivity and relaxation times in clays and porous media containing clays. This study, using for the first time both simulation and experimental approaches, aims to systematically investigate the surface relaxivity of clays characterized by variable mineralogy and iron content. A glass beads sample (iron free) and 5 different pure clay minerals samples (ranked by increasing iron content: Kaolinite, Smectite, Illite, Chlorite, and Nontronite) were prepared with similar average grain sizes (500 μm). The determination of surface relaxivity requires prior measurement of pore surface-to-volume ratio (S/V) using an independent method in addition to obtaining T2 relaxation time. Two methods, among the most widely used, were used here for S/V determination including BET N2 gas adsorption and 3D micro CT imaging. The 3D images were also used to conduct NMR simulations to reproduce the experimental data. The estimated surface relaxivity values from both methods were compared and correlated to the iron content of the different clays. The surface relaxivity values obtained based on BET-derived S/V showed reasonable values (29–343 μm/s) that have a strong positive relationship with iron content of the clays. The documented equation relating surface relaxivity and iron content can be potentially utilized to predict surface relaxivity based on the compositional analysis of clays. On the other hand, digital images did not capture the surface complexity of clays thus significantly underestimated S/V which consequently resulted in overestimated surface relaxivity (898–11000 μm/s) that were physically non-feasible. Supporting the same argument, the simulated T2 relaxation distribution showed significant mismatch with the experimental data for the clay samples while an excellent match was observed for the glass beads sample. This can be attributed to the smooth surface of the glass beads, unlike the complex clays. The reported surface relaxivity values (based on BET-derived S/V) for the individual clay minerals can be used to perform NMR simulation and interpretation studies conducted on sandstone or shale formations. Careful attention should be given when performing NMR simulation on micro-CT digital images of samples containing clay due to the inadequacy of such images in capturing the complex surface and microporous nature of clays. The outcomes from this study can improve the interpretation of NMR T2 data and the determination of NMR-derived pore size distribution and petrophysical properties. The reported surface relaxivity values for clay can also inform the NMR simulation.

Magnetic-assisted exciton-plasmon interactions modulated Bi2S3 nanorods@MoS2 nanosheets heterojunction: towards a split-type photoelectrochemical sensing of profenofos.

A split-type photoelectrochemical (PEC) sensor was designed for the detection of profenofos (PFF) depending on the magnetic-assisted exciton-plasmon interactions (EPI) between the semiconductor substrate and Au NPs. The core-shell Bi2S3 nanorods@MoS2 nanosheets (Bi2S3 NRs@MoS2 NSs) heterostructure nanomaterial with fascinating performance was synthesized and used as the photovoltaic conversion substrate and signal molecules absorption platform. The PEC sensor is operated by co-incubating with the released Au NPs-cDNA from the surface of magnetic beads, originating from the target-triggered DNA double-stranded structure opening event. Due to the strong EPI effects, the photocurrent of Bi2S3 NRs@MoS2 NSs decreased and varied with the PFF concentrations. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (1.0 pg mL-1~1.0 μg mL-1), low detection limitation (0.23 pg mL-1, at 3 σ/m), excellent specificity, high stability, and applicability. Overall, this work provides a new signal strategy for PEC biosensors and extends its application in environmental analysis.

A Self-Assembled G-Quadruplex/Hemin DNAzyme-Driven DNA Walker Strategy for Sensitive and Rapid Detection of Lead Ions Based on Rolling Circle Amplification.

Herein, a sensitive biosensor is constructed based on a novel rolling circle amplification (RCA) for colorimetric quantification of lead ion (Pb2+). At the detection system, GR5 DNAzymes are modified on the surface of an immunomagnetic bead, and Pb2+ is captured by the aptamer, inducing the disintegration of the GR5 DNAzyme and the release of the DNA walker. After the introduction of the template DNA, T4 DNA ligase, and phi29 DNA polymerase, an RCA is initiated for the sensitivity improvement of this method. Moreover, a G4-hemin DNAzyme is formed as a colorimetric signal, owing to its peroxide-like activity to catalyze the TMB-H2O2 substrate. Under the optimized conditions, the limit of detection (LOD) of this fabricated biosensor could reach 3.3 pM for Pb2+ with a concentration in the range of 0.01-1000 nM. Furthermore, the results of real samples analysis demonstrate its satisfactory accuracy, implying its great potential in the rapid detection of heavy metals in the environment.