Abstract
We report a broadly applicable enzyme digestion strategy for introducing structure-switching functionality into small-molecule-binding aptamers. This procedure is based on our discovery that ...exonuclease III (Exo III) digestion of aptamers is greatly inhibited by target binding. As a demonstration, we perform Exo III digestion of a pre-folded three-way-junction (TWJ)-structured cocaine-binding aptamer and a stem-loop-structured ATP-binding aptamer. In the absence of target, Exo III catalyzes 3′-to-5′ digestion of both aptamers to form short, single-stranded products. Upon addition of target, Exo III digestion is halted four bases prior to the target-binding domain, forming a major target-bound aptamer digestion product. We demonstrated that target-binding is crucial for Exo III inhibition. We then determine that the resulting digestion products of both aptamers exhibit a target-induced structure-switching functionality that is absent in the parent aptamer, while still retaining high target-binding affinity. We confirm that these truncated aptamers have this functionality by using an exonuclease I-based digestion assay and further evaluate this characteristic in an electrochemical aptamer-based cocaine sensor and a fluorophore-quencher ATP assay. We believe our Exo III-digestion method should be applicable for the generation of structure-switching aptamers from other TWJ- or stem-loop-containing small-molecule-binding aptamers, greatly simplifying the generation of functionalized sensor elements for folding-based aptasensors.
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•Radical assisted iron impregnation was used to prepare sludge precursors.•Radical oxidation promoted enhanced Fe3+ interaction with disintegrated sludge flocs.•The resulted catalyst ...had Fe NPs uniformly encapsulated in carbon matrix.•The resulted catalyst had much improved stability and activity.•Fe NPs distributed in pores facilitate the polar interaction with organic acids.
Radical induced sewage sludge pretreatment has been developed to enhance sludge stabilization and dewaterability. Except for anaerobic digestion, the reutilization of the oxidized sludge residuals is still a challenging issue for wastewater treatment plant. In the view of favorable role in sludge disintegration, the pretreated sludge precursors, which was obtained by sequential radical oxidation and iron impregnation, was carbonized to prepare the carbon encapsulated Fe nanoparticles (Fe NPs), which could then behave as highly stable and active heterogeneous Fenton-like catalyst to degrade Black-T. By contrast, the carbonized products derived from direct iron impregnation were also prepared as a control method. The effect of H2O2/Fe2+ on zeta potential, particle size, morphology and texture structure of the pretreated sludge precursors and their corresponding influence on the carbonized materials were systematically evaluated. Results showed that radicals’ activation could facilitate the iron impregnation on sewage sludge by rupturing the microbial aggregate and making them more accessible to subsequent microbial fragments. Compared to direct iron impregnation, the carbonized products featured much higher iron insertion rate and the uniformly dispersed Fe NPs encapsulated into porous carbons, which in turn enables catalysts exhibiting more efficient catalytic activity in continuous heterogeneous Fenton-like degradation and resistance to metal leaching.
Plant innate immunity plays an important role in regulating symbiotic associations with rhizobia, including during rhizobial infection, rhizobial colonization, and bacteroid differentiation in ...leguminous plants. Here we propose that an immune signaling pathway similar to plant pattern-triggered immunity (PTI) is required for the regulation of bacteroid differentiation in Medicago truncatula nodules.
DNA-modified gold nanoparticles (AuNPs) are useful signal-reporters for detecting diverse molecules through various hybridization- and enzyme-based assays. However, their performance is heavily ...dependent on the probe DNA surface coverage, which can influence both target binding and enzymatic processing of the bound probes. Current methods used to adjust the surface coverage of DNA-modified AuNPs require the production of multiple batches of AuNPs under different conditions, which is costly and laborious. We here develop a single-step assay utilizing dithiothreitol (DTT) to fine-tune the surface coverage of DNA-modified AuNPs. DTT is superior to the commonly used surface diluent, mercaptohexanol, as it is less volatile, allowing for the rapid and reproducible controlling of surface coverage on AuNPs with only micromolar concentrations of DTT. Upon adsorption, DTT forms a dense monolayer on gold surfaces, which provides antifouling capabilities. Furthermore, surface-bound DTT adopts a cyclic conformation, which reorients DNA probes into an upright position and provides ample space to promote DNA hybridization, aptamer assembly, and nuclease digestion. We demonstrate the effects of surface coverage on AuNP-based sensors using DTT-regulated DNA-modified AuNPs. We then use these AuNPs to visually detect DNA and cocaine in colorimetric assays based on enzyme-mediated AuNP aggregation. We determine that DTT-regulated AuNPs with lower surface coverage achieve shorter reaction times and lower detection limits relative to those for assays using untreated AuNPs or DTT-regulated AuNPs with high surface coverage. Additionally, we demonstrate that our DTT-regulated AuNPs can perform cocaine detection in 50% urine without any significant matrix effects. We believe that DTT regulation of surface coverage can be broadly employed for optimizing DNA-modified AuNP performance for use in biosensors as well as drug delivery and therapeutic applications.
We report a rapid and specific aptamer-based method for one-step cocaine detection with minimal reagent requirements. The feasibility of aptamer-based detection has been demonstrated with sensors ...that operate via target-induced conformational change mechanisms, but these have generally exhibited limited target sensitivity. We have discovered that the cocaine-binding aptamer MNS-4.1 can also bind the fluorescent molecule 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND) and thereby quench its fluorescence. We subsequently introduced sequence changes into MNS-4.1 to engineer a new cocaine-binding aptamer (38-GC) that exhibits higher affinity to both ligands, with reduced background signal and increased signal gain. Using this aptamer, we have developed a new sensor platform that relies on the cocaine-mediated displacement of ATMND from 38-GC as a result of competitive binding. We demonstrate that our sensor can detect cocaine within seconds at concentrations as low as 200 nM, which is 50-fold lower than existing assays based on target-induced conformational change. More importantly, our assay achieves successful cocaine detection in body fluids, with a limit of detection of 10.4, 18.4, and 36 μM in undiluted saliva, urine, and serum samples, respectively.
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•CoFe2O4@CNT-PMS system showed excellent efficiency for SMX degradation.•The confined effect was observed in the CoFe2O4@CNT-PMS system.•1O2 yield was enhanced by electron transfer ...and confined effect in CoFe2O4@CNT.•The interaction of CNT and CoFe2O4 in nanoconfined space was the key factor.
The efficiency of producing reactive species in advanced oxidation processes was one of the biggest challenges in increasing the performance of heterogeneous catalysts. The confined catalyst was synthesized by encapsulating CoFe2O4 spinel in carbon nanotube (CNT) towards the activation of peroxymonosulfate (PMS). This catalyst not only exhibited superior catalytic property for sulfamethoxazole degradation, but also rapidly degrade 91 % of sulfamethoxazole (SMX) within 10 min. CNT provided an ideal nanoconfined environment for the formation and growth of the CoFe2O4 nanoparticles. The confined effect of CoFe2O4@CNT towards PMS activation could be improved in two ways: (i) increasing the contact probability between SMX and PMS; (ii) enhancing the electron transfer process. The interactions of micropollutants, oxygenants and catalysts was strengthened in confined effects and 1O2 was triggered as the main reactive species for SMX degradation. Moreover, the confined environment of CNT encapsulated CoFe2O4 was improved, further influencing catalytic performance and stability. The recyclability of CoFe2O4@CNT denoted 87 % of SMX removal up to the 5th run of usage.
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•CNS nanoparticles were synthesized by a facile hydrothermal process.•CNS were incorporated into PVDF ultrafiltration membrane.•The composite membrane showed enhanced hydrophilicity ...and anti-fouling property.•The composite membrane showed better water flux and BSA rejection.
The hydrophobicity of polyvinylidene fluoride (PVDF) membrane in nature can result in permeability decline and critical membrane fouling, limiting its further development and application in the field of purification and separation. Novel composite PVDF ultrafiltration membranes containing 0.1–0.6 wt% of synthesized hydrothermal carbon nanospheres (CNS) were prepared with phase inversion method. The CNS had the mean diameter between 170 and 177 nm and the reactive oxygen functionalities such as hydroxyl, carbonyl, and carboxylic groups on outer carbon surface. The various characterizations revealed that the amount of CNS had a significant effect on composite membrane properties. The membrane of PVDF-2 exhibited the superior properties because of its lowest surface roughness and highest hydrophilicity, thermal stability, surface energy, porosity and mean pore size. Evaluations by pure water flux, bovine serum albumin (BSA) rejection and antifouling performance test further demonstrated the enhancement of membrane performance properties by the introduction of CNS into PVDF. The highest pure water flux, BSA rejection and flux recovery ratio (FRR) were achieved with the composite membrane blended with an amount of 0.2 wt% CNS (PVDF-2), reaching 956.72 L m−2 h−1, 95.8% and 83.21% respectively. The overall improved permeability and antifouling performance suggested a great potential application of carbonaceous spheres being used in composite PVDF membrane fabrication.
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•Preparation of highly porous biochar by combined pyrolysis and urine activation.•Urine converted to pore template in the 1st pyrolysis stage and was then in situ decomposed to form ...pores.•The sludge biochar possessed high BET surface area (253 m2/g) and pore volume (0.193 cm3/g).•The biochar had good adsorption capacity for EBT (21.9 mg/g).
Urine, which is composed of water, urea and mineral substance, has been treated as a kind of wastewater for a long time. In this work, urine was used as a novel activator for sludge activation and porous carbon preparation. The pyrolysis was implemented for urine transformation and sludge carbonization. It was found that urine was firstly converted to pore template g-C3N4 at 550℃ and g-C3N4 was in situ decomposed to form pores at 650℃ in the 2nd stage. The influence of pyrolysis temperature in each stage and urine to sludge ratio on properties of carbon was systematically investigated by using thermogravimetric analysis, N2 adsorption-desorption technique and transmission electron microscope. The maximum specific surface area of the produced carbon was 253 m2 g−1, which was equivalent to the carbon prepared by traditional H3PO4 activation. The carbon also had higher adsorption capacity (19.1 mg g−1) to a typical dye Eriochrome Black T (EBT) and meanwhile showed strong stability and reusability in the repeated adsorption cycles. The implementation of using urine as bio-waste activator for porous carbon preparation would have important implications for waste recycle and reutilization.
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•The sludge-based particle electrode (SPE) was used to enhance sludge dewaterability.•A three-dimensional electrochemical reactor was established with the addition of SPE.•The maximum ...reduction of capillary suction time was observed at 10 min and 10 V.•The excessive released biopolymers from sludge could be adsorbed by porous SPE.•The hydrophilic SPE could provide abundant channels for water release.
Electrochemical sludge conditioning was widely used to enhance sludge dewaterability. However, the limited area of plane electrodes results in poor dewatering efficiency and high energy consumption. The long period electrolysis with high cell voltage leads to the dissolution of extracellular polymeric substance (EPS), which accelerates the deterioration of sludge dewaterability. Herein, a clean and cost-saving method was proposed to enhance sludge dewaterability in this study. The capillary suction time (CST) of sludge conditioned with a three-dimensional electrochemical reactor (3D-ER) with sludge-based particle electrodes (SPE) decreased from 65.5 s to 29.6 s within 10 min while the water content decreased from 98.56% to 65.30% by mechanical filtration. The polarization of SPE in the electric field induced significant sludge flocs decomposition and EPS dissolution with a low energy consumption of 0.0020 kWh·L−1. The addition of commercial activated carbon (CAC) and SPE increased the calorific value of dewatered sludge as solid fuels. The SPE with the hydrophilic groups and silicon oxide provided more polar channels for water release than CAC, leading to an enhanced sludge dewaterability. These findings provided a new insight for improving sludge dewaterability and resource utilization in a closed loop in wastewater treatment plants.
On-site detection of multiple small-molecule analytes in complex sample matrixes would be highly valuable for diverse biosensing applications. Paper electrochemical devices (PEDs) offer an especially ...appealing sensing platform for such applications due to their low cost, portability, and ease of use. Using oligonucleotide-based aptamers as biorecognition elements, we here for the first time have developed a simple, inexpensive procedure for the fabrication of aptamer-modified multiplex PEDs (mPEDs), which can robustly and specifically detect multiple small molecules in complex samples. These devices are prepared via an ambient vacuum filtration technique using carbon and metal nanomaterials that yields precisely patterned sensing architecture featuring a silver pseudo-reference electrode, a gold counter electrode, and three gold working electrodes. The devices are user-friendly, and the fabrication procedure is highly reproducible. Each working electrode can be readily modified with different aptamers for sensitive and accurate detection of multiple small-molecule analytes in a single sample within seconds. We further demonstrate that the addition of a PDMS chamber allows us to achieve detection in microliter volumes of biological samples. We believe this approach should be highly generalizable, and given the rapid development of small-molecule aptamers, we envision that facile on-site multi-analyte detection of diverse targets in a drop of sample should be readily achievable in the near future.
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