A novel ratiometric sensor for fluorimetric and visual dual-mode detection of Al3+ in environmental water based on the target-regulated formation of Eu MOFs.

Herein, a novel ratiometric sensor for fluorimetric and smartphone-assisted visual detection of Al3+ in environmental water was developed based on the target-regulated formation of Eu metal-organic frameworks (Eu MOFs). By employing 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethanesulfonic acid (Hepes), Eu3+ and tetracycline (TC) as raw materials, Eu MOFs with red emission were facilely synthesized through the coordination of Eu3+ with Hepes and TC. However, upon the introduction of Al3+, a higher affinity of TC towards Al3+ resulted in the formation of a TC-Al3+ complex with green fluorescence and inhibited the generation of Eu MOFs. This led to an increase in green fluorescence and a decrease in red fluorescence accompanied by the fluorescence color of the solution changing from red to green under the illumination of the UV lamp. Thus, a ratiometric sensor for fluorimetric and the smartphone-assisted visual detection of Al3+ was established. The ratiometric sensor exhibited high sensitivity for Al3+ detection with a detection limit of 0.14 µM for fluorescence detection and 1.21 µM for visual detection. Additionally, the proposed strategy was successfully applied to detect Al3+ in the environmental water samples with satisfactory results, indicating great application prospects for environmental monitoring.

A facile fluorescence Eu MOF sensor for ascorbic acid and ascorbate oxidase detection.

In this work, a facile fluorescence Eu3+-based metal-organic framework (Eu MOF) sensor for ascorbic acid (AA) and ascorbate oxidase (AAO) detection was developed. The fluorescence of the Eu MOF could be effectively quenched by Ce3+ but not by Ce4+ at an appropriate concentration, and thus, when the reductant AA was added into the solution containing Ce4+, Ce4+ was chemically reduced to Ce3+, which induced the decreased fluorescence signal of the Eu MOF. However, when AAO was introduced, AA was effectively oxidized to dehydroascorbic acid (DHAA) under the catalysis of AAO, and thus, Ce4+ could not be reduced, resulting in the fluorescence restoration of the Eu MOF. Hence, the concentration of AA and AAO could be determined by the fluorescence decrease and restoration of the Eu MOF. The fluorescent platform showed high sensitivity with a limit of detection of 0.32 µM for AA and 1.18 U L-1 for AAO, respectively. Moreover, the proposed method was successfully applied for AA and AAO determination in real samples, indicating great potential for biomedical application in complex matrices.

A redox modulated fluorescence nanoplatform for the detection of alkaline phosphatase activity with fluorescent polydopamine nanoparticles.

Herein, we simply synthesized intrinsic fluorescent polydopamine nanoparticles (PDA NPs) in sodium hydroxide solution (NaOH, pH 11), and constructed a new fluorescence nanoplatform for the detection of alkaline phosphatase (ALP) using PDA NPs as an effective signal reporter. The nanoplatform was constructed by the combination of enzymatic hydrolysis of ALP to the substrate l-ascorbic acid-2-phosphate (AA2P) and the chemical redox reaction between l-ascorbic acid (AA) and mercury ion (Hg2+). The fluorescence of PDA NPs could be effectively quenched by Hg2+ through the coordination effect between Hg2+ and the functional groups on the surface of PDA NPs. However, the quenching effect was greatly inhibited by the addition of AA into the solution. Based on this point, the activity of ALP could be monitored by hydrolysis of the substrate AA2P to AA and the fluorescence output of PDA NPs. The nanoplatform exhibited high sensitivity and desirable selectivity for ALP detection. With a wide linear range of 0 to 18 U L-1, a detection limit of 0.4 U L-1 was achieved using the developed nanosensor. The proposed method could not only be used to screen the inhibitor of ALP but also be used to detect ALP activity in human serum samples successfully. Moreover, the strategy can easily be expanded to determining other kinds of enzymes participating in AA-generation reactions.

Fluorescent polydopamine nanoparticles as a nanosensor for the sequential detection of mercury ions and l-ascorbic acid based on a coordination effect and redox reaction.

Herein, a novel fluorescence nanosensor using intrinsic fluorescent polydopamine nanoparticles (PDA NPs) as an effective signal reporter has been constructed for the simple, rapid and sequential detection of mercury ions (Hg2+) and l-ascorbic acid (AA) based on a coordination effect and redox reaction. The fluorescence of the PDA NPs could be specifically quenched by Hg2+ through intense coordination effects between the Hg2+ and the groups (catechol, amine, ketone and imine) on the surface of the PDA NPs. However, when AA and Hg2+ coexisted in solution, the fluorescence of the PDA NPs pronouncedly recovered via the redox reaction of Hg2+, with it being reduced to Hg0 by AA. The fluorescence quenching mechanism of Hg2+ towards the PDA NPs and the redox reaction between Hg2+ and AA were also fully investigated. The nanosensor exhibited high sensitivity and desirable selectivity for Hg2+ and AA detection. Moreover, the strategy was successfully explored in real samples (tap water, lake water and human serum samples) with satisfactory recoveries. The developed nanosensor provides new sights and good inspiration for Hg2+ and AA detection under real conditions.

MnO2 Nanosheet-based Fluorescence Sensing Platform for Sensitive Detection of Endonuclease.

A novel fluorescence sensing platform for ultrasensitive detection of S1 nuclease activity has been constructed based on MnO2 nanosheets and FAM labeled single-stranded DNA (FAM-ssDNA). In this system, MnO2 nanosheets were found to have different adsorbent ability toward ssDNA and mono- or oligonucleotide fragments. FAM-ssDNA could adsorb on MnO2 nanosheets and resulted in significant fluorescence quenching through fluorescence resonance energy transfer (FRET), while mono- or oligonucleotide fragments could not adsorb on MnO2 nanosheets and still retained strong fluorescence emission. With the addition of S1 nuclease, FAM-ssDNA was cleaved into mono- or oligonucleotide fragments, which were not able to adsorb on MnO2 nanosheets and the fluorescence signal was never quenched. The different fluorescence intensity allowed for examination of S1 nuclease activity. The developed method can detect S1 nuclease activity in the range of 0 - 20 U mL-1 with a detection limit of 0.05 U mL-1. Benefits of the system include less time-consuming processes and more simple design compared to other endonuclease assays. Satisfactory performance for S1 nuclease in complex samples has been successfully demonstrated with the system. The developed assay could potentially provide a new platform in bioimaging and clinical diagnosis.

Reduction in greenhouse gas emissions from sludge biodrying instead of heat drying combined with mono-incineration in China.

Sludge is an important source of greenhouse gas (GHG) emissions, both in the form of direct process emissions and as a result of indirect carbon-derived energy consumption during processing. In this study, the carbon budgets of two sludge disposal processes at two well-known sludge disposal sites in China (for biodrying and heat-drying pretreatments, both followed by mono-incineration) were quantified and compared. Total GHG emissions from heat drying combined with mono-incineration was 0.1731 tCO2e t-1, while 0.0882 tCO2e t-1 was emitted from biodrying combined with mono-incineration. Based on these findings, a significant reduction (approximately 50%) in total GHG emissions was obtained by biodrying instead of heat drying prior to sludge incineration. IMPLICATIONS: Sludge treatment results in direct and indirect greenhouse gas (GHG) emissions. Moisture reduction followed by incineration is commonly used to dispose of sludge in China; however, few studies have compared the effects of different drying pretreatment options on GHG emissions during such processes. Therefore, in this study, the carbon budgets of sludge incineration were analyzed and compared following different pretreatment drying technologies (biodrying and heat drying). The results indicate that biodrying combined with incineration generated approximately half of the GHG emissions compared to heat drying followed by incineration. Accordingly, biodrying may represent a more environment-friendly sludge pretreatment prior to incineration.

MnO2-induced synthesis of fluorescent polydopamine nanoparticles for reduced glutathione sensing in human whole blood.

Polydopamine (PDA) nanoparticles, as a kind of popular polymer material, have attracted a great deal of attention from various areas including materials science, biomedicine, energy, environmental science and so on owing to their striking physicochemical properties. Herein, we reported for the first time the synthesis of intrinsic fluorescent PDA nanoparticles using MnO2 as an oxidant. In the presence of MnO2, dopamine was quickly oxidized into its quinone derivative, and autopolymerized into fluorescent PDA nanoparticles. Using fluorescent PDA nanoparticles as a fluorescence signal indicator, we further established a cost-effective sensor for rapid, sensitive and selective sensing of reduced glutathione (GSH) based on the redox reaction between MnO2 and GSH, and the key role of MnO2 in the formation of fluorescent PDA nanoparticles. GSH has the capability of reducing MnO2 into Mn(2+), which inhibited the formation of the fluorescent PDA nanoparticles. Thus, the concentration of GSH was directly related to the decreased fluorescence signal intensity of the PDA nanoparticles. The sensor showed good sensing performance for GSH detection with high sensitivity and desirable selectivity over other potential interfering species. Additionally, the sensor exhibited excellent practical applications for GSH detection in human whole blood samples, which presents potential applications in biological detection and clinical diagnosis.

Endonuclease IV cleaves apurinic/apyrimidinic sites in single-stranded DNA and its application for biosensing.

Endonuclease IV (Endo IV), as a DNA repairing enzyme, plays a crucial role in repairing damaged DNA comprising abasic sites to maintain genomic integrity. The cleaving capability of Endo IV to apurinic/apyrimidinic sites (AP) in single-stranded DNA (ssDNA) was demonstrated. It was found that Endo IV has considerably high cleaving activity to AP sites in ssDNA compared with that in double-stranded DNA (dsDNA). The unique feature of Endo IV in cleaving AP sites in ssDNA was further applied to construct a novel dual signal amplified sensing system for highly sensitive enzyme and protein detection by a combination of exonuclease III (Exo III)-aided cyclic amplification reaction and a rolling circle replication (RCR) technique, which showed a good sensing performance with a detection limit of 0.008 U mL(-1) for Endo IV and 2.5 pM for streptavidin. In addition, the developed method had considerably high specificity for Endo IV and streptavidin over other potential interferences. The developed strategy indeed provides a novel platform for protein and enzyme assays and may find a broad spectrum of applications in bioanalysis, disease diagnosis, and drug development.

Fabrication of a LRET-based upconverting hybrid nanocomposite for turn-on sensing of H2O2 and glucose.

Blood glucose detecting has aroused considerable attention because diabetes mellitus has become a worldwide publish health problem. Herein, we construct an exceptionally simple upconverting hybrid nanocomposite, composed of DNA-templated Ag nanoparticles (DNA-AgNPs) and NaYF4:Yb/Tm@NaYF4 core-shell upconversion nanoparticles (UCNPs), for the sensing of H2O2 and glucose. In this design, UCNPs with bared surface act as the donor, and DNA-AgNPs serve as efficient quenchers. DNA-AgNPs can be directly assembled on the bared surface of UCNPs, which further decreases the distance of donor-to-acceptor. The formation of DNA-AgNPs/UCNP nanocomposite results in luminescence quenching of UCNP by DNA-AgNPs through luminescence resonance energy transfer (LRET). Upon H2O2 addition, AgNPs can be etched and transformed into Ag(+), leading to inhibition of the LRET process and causing the recovery of upconversion luminescence. Based on the conversion of glucose into H2O2 by glucose oxidase, the DNA-AgNPs/UCNP nanocomposite can also be exploited for glucose sensing. Moreover, due to the non-autofluorescence offered by UCNPs, the approach developed can be applied to monitor glucose levels in human serum samples with satisfactory results.

"Light-up" Sensing of human 8-oxoguanine DNA glycosylase activity by target-induced autocatalytic DNAzyme-generated rolling circle amplification.

Human 8-oxoguanine DNA glycosylase (hOGG1) plays a crucial role in maintaining the genomic integrity of living organisms for its capability of repairing DNA oxidative damage. The expression level of hOGG1 is closely associated with many diseases including various kinds of cancers. In this study, a novel "light-up" sensor based on target-induced formation of 5' phosphorylated probe and autocatalytic DNAzyme-generated rolling circle amplification has been developed for highly sensitive human 8-oxoguanine DNA glycosylase (hOGG1) activity assay. The approach reaches detection limit as low as 0.001U/mL for hOGG1 via scarcely increased background signal and dual signal amplification strategy. To the best of our knowledge, it is one of the most sensitive methods for the detection of base excision repair enzyme. Moreover, the approach shows excellent specificity over other nonspecific enzymes would interfere with the assay and holds great promise for application in real sample analysis. Hence, the proposed method provides a highly sensitive, selective, and desirable hOGG1 sensing platform.

Phosphorylation-induced formation of a cytochrome c-peptide complex: a novel fluorescent sensing platform for protein kinase assay.

A novel fluorescent sensing platform has been developed for protein kinase assay based on the phosphorylation-induced formation of a cytochrome c-peptide complex.

A cobalt oxyhydroxide-modified upconversion nanosystem for sensitive fluorescence sensing of ascorbic acid in human plasma.

Ascorbic acid (AA), a potent antioxidant readily scavenging reactive species, is a crucial micronutrient involved in many biochemical processes. Here, we have developed a cobalt oxyhydroxide (CoOOH)-modified upconversion nanosystem for fluorescence sensing of AA activity in human plasma. The nanosystem consists of upconversion nanoparticles (UCNPs) NaYF4:30% Yb,0.5% Tm@NaYF4, which serve as energy donors, and CoOOH nanoflakes formed on the surface of UCNPs, which act as efficient energy acceptors. The fluorescence resonance energy transfer (FRET) process from the UCNPs to the absorbance of the CoOOH nanoflakes occurs in the nanosystem. The AA-mediated specific redox reaction reduces CoOOH into Co(2+), leading to the inhibition of FRET, and resulting in the recovery of upconversion emission spectra. On the basis of these features, the nanosystem can be used for sensing AA activity with sensitivity and selectivity. Moreover, due to the minimizing background interference provided by UCNPs, the nanosystem has been applied to monitoring AA levels in human plasma sample with satisfactory results. The proposed approach may potentially provide an analytical platform for research and clinical diagnosis of AA related diseases.

A G-quadruplex-based Label-free Fluorometric Aptasensor for Adenosine Triphosphate Detection.

A G-quadruplex-based, label-free fluorescence assay was demonstrated for the detection of adenosine triphosphate (ATP). A double-stranded DNA (dsDNA), hybridized by ATP-aptamer and its complementary sequence, was employed as a substrate for ATP binding. SYBR Green I (SG I) was a fluorescent probe and exonuclease III (Exo III) was a nuclease to digest the dsDNA. Consequently, in the absence of ATP, the dsDNA was inset with SG I and was digested by Exo III, resulting in a low background signal. In the presence of ATP, the aptamer in dsDNA folded into a G-quadruplex structure that resisted the digestion of Exo III. SG I was inserted into the structure, showing high fluorescence. Owing to a decrease of the background noise, a high signal-to-noise ratio could be obtained. This sensor can detect ATP with a concentration ranging from 50 µM to 5 mM, and possesses a capacity for the sensitive determination of other targets.

MnO2-Nanosheet-Modified Upconversion Nanosystem for Sensitive Turn-On Fluorescence Detection of H2O2 and Glucose in Blood.

Blood glucose monitoring has attracted extensive attention because diabetes mellitus is a worldwide public health problem. Here, we reported an upconversion fluorescence detection method based on manganese dioxide (MnO2)-nanosheet-modified upconversion nanoparticles (UCNPs) for rapid, sensitive detection of glucose levels in human serum and whole blood. In this strategy, MnO2 nanosheets on the UCNP surface serve as a quencher. UCNP fluorescence can make a recovery by the addition of H2O2, which can reduce MnO2 to Mn(2+), and the glucose can thus be monitored based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2. Because of the nonautofluorescent assays offered by UCNPs, the developed method has been applied to monitor glucose levels in human serum and whole blood samples with satisfactory results. The proposed approach holds great potential for diabetes mellitus research and clinical diagnosis. Meanwhile, this nanosystem is also generalizable and can be easily expanded to the detection of various H2O2-involved analytes.

A new label-free and turn-on strategy for endonuclease detection using a DNA-silver nanocluster probe.

Endonuclease plays a vital role in a variety of biological processes and the assay of endonuclease activity and inhibitors is of high importance in the fields ranging from biotechnology to pharmacology. Howerer, traditional techniques usually suffer from time intensive, laborious, and cost-expensive. This work aims to develop a facile and sensitive method for endonuclease activity assay by making use of the fluorescence enhancement effect when DNA-silver nanoclusters (DNA-Ag NCs) are in proximity to guanine-rich DNA sequences. The system mainly consists of block DNA (B-DNA), G-DNA and Ag-DNA. B-DNA serves as the substrate of the endonuclease (S1 nuclease as the model enzyme). G-DNA, which is predesigned entirely complementary to B strand, contains a guanine-rich overhang sequence and hybridization part at the 5'-end. Ag-DNA involves a sequence for Ag NCs synthesis and a sequence complementary to the hybridization part of the G-DNA. In the "off" state, B-DNA plays the role as a blocker that inhibit the proximity between Ag NCs and guanine-rich DNA sequences, resulting in a low fluorescence readout. However, if S1 nuclease is introduced into the system, B-DNA was cleaved into mono- or short-oligonucleotides fragments, which could not hybridize with G-DNA. As a result, the subsequent addition of DNA-Ag NCs could bring guanine-rich DNA sequences close to the Ag NCs, accompanied by a significant fluorescence enhancement. Therefore, endonuclease activity could be successfully quantified by monitoring the variation in fluorescence intensity. In addition, this approach can also be applied for inhibitor screening of endonuclease. This label-free and turn-on fluorescent assays employing the mechanism proposed here for the detection of nuclease and inhibitors turn out to be sensitive, selective, and convenient.

Phospholipid-modified upconversion nanoprobe for ratiometric fluorescence detection and imaging of phospholipase D in cell lysate and in living cells.

Phospholipase D (PLD) is a critical component of intracellular signal transduction and has been implicated in many important biological processes. It has been observed that there are abnormalities in PLD expression in many human cancers, and PLD is thus recognized as a potential diagnostic biomarker as well as a target for drug discovery. We report for the first time a phospholipid-modified nanoprobe for ratiometric upconversion fluorescence (UCF) sensing and bioimaging of PLD activity. The nanoprobe can be synthesized by a facile one-step self-assembly of a phospholipid monolayer composed of poly(ethylene glycol) (PEG)ylated phospholipid and rhodamine B-labeled phospholipid on the surface of upconversion nanoparticles (UCNPs) NaYF4: 20%Yb, 2%Er. The fluorescence resonance energy transfer (FRET) process from the UCF emission at 540 nm of the UCNPs to the absorbance of the rhodamine B occurs in the nanoprobe. The PLD-mediated hydrolysis of the phosphodiester bond makes rhodamine B apart from the UCNP surface, leading to the inhibition of FRET. Using the unaffected UCF emission at 655 nm as an internal standard, the nanoprobe can be used for ratiometric UCF detection of PLD activity with high sensitivity and selectivity. The PLD activity in cell lysates is also determined by the nanoprobe, confirming that PLD activity in a breast cancer cell is at least 7-fold higher than in normal cell. Moreover, the nanoprobe has been successfully applied to monitoring PLD activity in living cells by UCF bioimaging. The results reveal that the nanoprobe provides a simple, sensitive, and robust platform for point-of-care diagnostics and drug screening in biomedical applications.

Efficiency influence of exogenous betaine on anaerobic sequencing batch biofilm reactor treating high salinity mustard tuber wastewater.

When treating a composite mustard tuber wastewater with high concentrations of salt (about 20 g Cl(-) L(-1)) and organics (about 8000 mg L(-1) COD) by an anaerobic sequencing batch biofilm reactor (ASBBR) in winter, both high salinity and low temperature will inhibit the activity of anaerobic microorganisms and lead to low treatment efficiency. To solve this problem, betaine was added to the influent to improve the activity of the anaerobic sludge, and an experimental study was carried to investigate the influence of betaine on treating high salinity mustard tuber wastewater by the ASBBR. The results show that, when using anaerobic acclimated sludge in the ASBBR, and controlling biofilm density at 50% and water temperature at 8-12 degrees C, the treatment efficiency of the reactor could be improved by adding the betaine at different concentrations. The efficiency reached the highest when the optimal dosage ofbetaine was 0.5 mmol L(-1). The average effluent COD, after stable acclimation, was 4461 mg L(-1). Relative to ASBBR without adding betaine, the activity of the sludge increased significantly. Meanwhile, the dehydrogenase activity of anaerobic microorganisms and the COD removal efficiency were increased by 18.6% and 18.1%, respectively.

Fractional, biodegradable and spectral characteristics of extracted and fractionated sludge extracellular polymeric substances.

Correlation between fractional, biodegradable and spectral characteristics of sludge extracellular polymeric substances (EPS) by different protocols has not been well established. This work extracted sludge EPS using alkaline extractants (NH4OH and formaldehyde + NaOH) and physical protocols (ultrasonication, heating at 80 °C or cation exchange resin (CER)) and then fractionated the extracts using XAD-8/XAD-4 resins. The alkaline extractants yielded more sludge EPS than the physical protocols. However, the physical protocols extracted principally the hydrophilic components which were readily biodegradable by microorganisms. The alkaline extractants dissolved additional humic-like substances from sludge solids which were refractory in nature. Different extraction protocols preferably extracted EPS with distinct fractional, biodegradable and spectral characteristics which could be applied in specific usages.