Development of a rapid visual detection technology for BmNPV based on CRISPR/Cas13a system.

Pathogenic microorganism of silkworm are important factors that threaten the high-quality development of sericulture. Among them, Bombyx mori nucleopolyhedrovirus (BmNPV) caused diseases often lead to frequent outbreaks and high mortality, resulting in huge losses to sericultural industry. Current molecular detection methods for BmNPV require expensive equipment and sikilled technical personnel. As a result, the most commonly detection method for silkworm egg production enterprises involves observing the presence of polyhedra under a microscope. However, this method has low accuracy and sensitivity. There is an urgent need to develop a new detection technology with high sensitivity, high specificity, and applicability for silkworm farms, silkworm egg production enterprises and quarantine departments. In this study, we successfully established the CRISPR/Cas13a BmNPV visualized detection technology by combining Recombinase Polymerase Amplification (RPA) technology and CRISPR/Cas13a system. This technology is based on microplate lateral, flow test strips and portable fluorescence detector. The detection sensitivity can reach up to 1 copies/µL for positive standard plasmid and 1 fg/µL for BmNPV genome in 30-45 min, demonstrating high sensitivity. By detecting silkworm tissues infected with different pathogens, we determined that CRISPR/Cas13a detection technology has good specificity. In summary, the newly established nucleic acid detection technology for BmNPV is characterized by high sensitivity, high specificity, low cost and convenience for visualization. It can be applied in field detection and silkworm egg quality monitory system.

Pathway analysis of spermidine anti-oxidative stress and inducing autophagy in granulosa cells of Sichuan white geese.

Spermidine, a natural polyamine, has been proven antioxidant function, but its pathway and mechanism of action remain unclear. Based on the oxidative stress model by 3-nitropropionic acid (3-NPA), the study explored the pathways by spermidine to rescue oxidative stress via autophagic process in goose granulosa cells by RNA-seq and RNA interference. In transcriptional regulation, in addition to KEGG pathways related to cell proliferation and differentiation, lots of KEGG pathways associated with inflammation, metabolism, and signaling were also significantly enriched in 3-NPA vs. 3-NPA + spermidine treatments. Six key genes (JUN, CD44, KITLG, RND2, BMP4 and KALRN) involved in spermidine-mediated anti-oxidative stress were screened. Furthermore, the experimental results showed that spermidine (80 µmol/L) significantly increased autophagic gene expression in goose granulosa cells, while EP300-siRNA or MAP1S-siRNA also significantly increased autophagic process. The autophagic gene expressions were no difference between EP300-siRNA and EP300-siRNA + spermidine treatments, although spermidine significantly increased autophagic process of granulosa cells compared to MAP1S-siRNA alone. In addition, inhibition of mTOR pathway significantly increased autophagic gene expression, which was further enhanced by spermidine in combined with mTOR inhibitor. These results suggest that spermidine can alleviate oxidative stress by inducing autophagy regulated by EP300, MAP1S and mTOR as well as regulating other independent gene expressions in goose granulosa cells.

NIR-driven photoelectrochemical-fluorescent dual-mode biosensor based on bipedal DNA walker for ultrasensitive detection of microRNA.

Optical biosensors have become powerful tools for bioanalysis, but most of them are limited by optic damage, autofluorescence, as well as poor penetration ability of ultraviolet (UV) and visible (Vis) light. Herein, a near-infrared light (NIR)-driven photoelectrochemical (PEC)-fluorescence (FL) dual-mode biosensor has been proposed for ultrasensitive detection of microRNA (miRNA) based on bipedal DNA walker with cascade amplification. Fueled by toehold-mediated strand displacement (TMSD), the bipedal DNA walker triggered by target miRNA-21 is formed through catalytic hairpin assembly (CHA), which can efficiently move along DNA tracks on CdS nanoparticles (CdS NPs)-modified fluorine doped tin oxide (FTO) electrode, resulting in the introduction of upconversion nanoparticles (UCNPs) on electrode surface. Under 980 nm laser irradiation, the UCNPs serve as the energy donor to emit UV/Vis light and excite CdS NPs to generate photocurrent for PEC detection, while the upconversion luminescence (UCL) at 803 nm is monitored for FL detection. This PEC-FL dual-mode biosensor has achieved the ultrasensitive and accurate analysis of miRNA-21 in human serum and different gynecological cancer cells. Overall, the proposed dual-mode biosensor can not only couple the inherent features of each single-mode biosensor but also provide mutual authentication of testing results, which opens up a new avenue for early diagnosis of miRNA-related diseases in clinic.

Recent Updates on Multifunctional Nanomaterials as Antipathogens in Humans and Livestock: Classification, Application, Mode of Action, and Challenges.

Pathogens cause infections and millions of deaths globally, while antipathogens are drugs or treatments designed to combat them. To date, multifunctional nanomaterials (NMs), such as organic, inorganic, and nanocomposites, have attracted significant attention by transforming antipathogen livelihoods. They are very small in size so can quickly pass through the walls of bacterial, fungal, or parasitic cells and viral particles to perform their antipathogenic activity. They are more reactive and have a high band gap, making them more effective than traditional medications. Moreover, due to some pathogen's resistance to currently available medications, the antipathogen performance of NMs is becoming crucial. Additionally, due to their prospective properties and administration methods, NMs are eventually chosen for cutting-edge applications and therapies, including drug administration and diagnostic tools for antipathogens. Herein, NMs have significant characteristics that can facilitate identifying and eliminating pathogens in real-time. This mini-review analyzes multifunctional NMs as antimicrobial tools and investigates their mode of action. We also discussed the challenges that need to be solved for the utilization of NMs as antipathogens.

Effects of exogenous spermidine on autophagy and antioxidant capacity in ovaries and granulosa cells of Sichuan white geese.

Autophagy can inhibit ovarian senescence induced by oxidative stress and regulate follicle development and atresia, but its mechanism is still unclear. Exogenous spermidine can induce autophagy and scavenge reactive oxygen species (ROS). In this experiment, oxidative stress in Sichuan white geese ovaries and follicular granulosa cells (GCs) was caused by 3-nitropropionic acid (3-NPA) and spermidine was added to explore the effect of exogenous spermidine inducing autophagy and inhibiting oxidative stress in vivo and in vitro. Research results showed that putrescine, spermidine and spermine contents in goose ovaries in the group treated with spermidine combined with 3-NPA were 2.70, 1.94, and 1.70 times higher than those in the group treated with 3-NPA, respectively (P < 0.05). The contents of spermidine and spermine in GCs were 1.37 and 0.89 times higher in the spermidine in combination with the 3-NPA group than in the 3-NPA group, respectively (P < 0.05). LC3 and p62 were mainly expressed in the follicular granulosa layer. The LC3-II/I ratio and p62 level in GCs in the spermidine combined with 3-NPA treatment group were 1.37 and 0.77 times higher than that of the 3-NPA treatment group, respectively (P < 0.05). 3-NPA treatment significantly increased ROS level and the apoptosis rate in GCs, while the combined treatment of spermidine and 3-NPA reversed this change (P < 0.05). In conclusion, spermidine alleviated the oxidative damage induced by 3-NPA by improving the antioxidant capacity of ovaries and follicular GCs of Sichuan white geese and may be alleviated by inducing autophagy in GCs.

This study investigated the effects of exogenous spermidine on oxidative stress induced by 3-nitropropionic acid (3-NPA) in ovaries and granulosa cells of Sichuan white geese. In ovarian tissue, spermidine can reduce malondialdehyde accumulation induced by 3-NPA by increasing antioxidant enzyme activity, thus alleviating the oxidative damage induced by 3-NPA. In addition, spermidine can also improve the morphological structure of follicles and alleviate the structural damage caused by 3-NPA. Our results showed that autophagy-associated proteins are mainly concentrated in the granulosa layer of follicles and spermidine can alter their expression. Subsequently, we found that spermidine could induce autophagy and reduce the accumulation of reactive oxygen species and apoptosis rate induced by 3-NPA in granulosa cells. Therefore, we speculate that spermidine can alleviate oxidative stress induced by 3-NPA by inducing autophagy in granulosa cells. In conclusion, spermidine can relieve oxidative stress induced by 3-NPA by increasing the activity of antioxidant enzymes, and may also relieve oxidative stress by inducing autophagy.

A biosensor based on Fe3O4@MXene-Au nanocomposites with high peroxidase-like activity for colorimetric and smartphone-based detection of glucose.

A novel magnetic nanozyme Fe3O4@MXene-Au nanocomposite, which possessed higher peroxidase-like activity than that of Fe3O4 nanoparticles and Fe3O4@MXene nanocomposites, was developed. The outstanding magnetic properties of the nanozyme endowed it with the ability of simple and rapid separation, achieving great recyclability. Based on Fe3O4@MXene-Au nanocomposites and glucose oxidase (Glu Ox), a highly selective colorimetric biosensor for glucose detection was developed. Fe3O4@MXene-Au nanocomposites can catalyze H2O2 produced from glucose catalyzed by glucose oxidase to ·OH and oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) with a significant absorbance at 652 nm. The linear range of glucose was 0-1.4 mM under optimal conditions, with a limit of detection (LOD) of 0.11 mM. Glucose in human whole blood was successfully detected with satisfactory recoveries. Furthermore, a facile agarose hydrogel detection platform was designed. With smartphone software, glucose detection can be realized by the agarose hydrogel platform, demonstrating the potential in on-site and visual detection of glucose.

Spermidine alleviating oxidative stress and apoptosis by inducing autophagy of granulosa cells in Sichuan white geese.

Spermidine have been reported a role in antioxidative, antiaging, and antiinflammatory. Oxidative stress causes granulosa cell (GC) apoptosis, follicular atresia, and impairs poultry reproductive functions. Studies have found that autophagy is the protective mechanism against antioxidant stress and apoptosis in cells. However, the relationship between spermidine-induced autophagy, oxidative stress, and apoptosis in goose GCs remains unclear. In this study, we investigated the autophagy mechanism to mediate spermidine effects on the alleviation of oxidative stress and apoptosis in goose GCs. Follicular GCs were treated with spermidine combination with 3-Nitropropanoic acid (3-NPA), rapamycin (RAPA), and chloroquine (CQ) or with hydrogen peroxide, RAPA, and CQ. Spermidine upregulated the ratio of LC3-II/I, inhibited the accumulation of p62 protein, and induced autophagy. 3-NPA treatment significantly increased ROS production, MDA content, SOD activity, cleaved CASPASE-3 protein expression, and decreased BCL-2 protein expression in follicular GCs. Spermidine inhibited oxidative stress and apoptosis induced by 3-NPA. In addition, hydrogen peroxide-induced oxidative stress was inhibited by spermidine. However, the inhibitory effect of spermidine was eliminated under chloroquine. Our results demonstrated that spermidine relieved oxidative stress and apoptosis of GCs by inducing autophagy, indicating that spermidine has a great potential to maintain proteostasis and sustain granulosa cell viability in geese.

Sera Metabolomics Characterization of Patients at Different Stages in Wuhan Identifies Critical Biomarkers of COVID-19.

We have witnessed the 2-year-long global rampage of COVID-19 caused by the wide spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, knowledge about biomarkers of the entire COVID-19 process is limited. Identification of the systemic features of COVID-19 will lead to critical biomarkers and therapeutic targets for early intervention and clinical disease course prediction. Here, we performed a comprehensive analysis of clinical measurements and serum metabolomics in 199 patients with different stages of COVID-19. In particular, our study is the first serum metabolomic analysis of critical rehabilitation patients and critical death patients. We found many differential metabolites in the comparison of metabolomic results between ordinary, severe, and critical patients and uninfected patients. Through the metabolomic results of COVID-19 patients in various stages, and critical rehabilitation patients and critical death patients, we identified a series of differential metabolites as biomarkers, a separate queue and precise distinction, and predicted COVID-19 verification. These differentially expressed metabolites, included 1,2-di-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphate, propylparaben, 20-hydroxyeicosatetraenoic acid, triethanolamine, chavicol, disialosyl galactosyl globoside, 1-arachidonoylglycerophosphoinositol, and alpha-methylstyrene, all of which have been identified for the first time as biomarkers in COVID-19 progression. These biomarkers are involved in many pathological and physiological pathways of COVID-19, for example, immune responses, platelet degranulation, and metabolism which might result in pathogenesis. Our results showed valuable information about metabolites obviously altered in COVID-19 patients with different stages, which could shed light on the pathogenesis as well as serve as potential therapeutic agents of COVID-19.

A biosensor based on the biomimetic oxidase Fe3O4@MnO2 for colorimetric determination of uric acid.

High plasma urate is closely related to gout, cardiovascular and other diseases. Therefore, monitoring the content of uric acid (UA) in plasma is of great significance for the treatment of gout and the prevention of other related diseases. Herein, a biosensor based on the biomimetic oxidase Fe3O4 nanoparticles (NPs) @MnO2 nanosheets (Fe3O4@MnO2 NS) was constructed for colorimetric determination of UA. MnO2 NS is an efficient biomimetic oxidase, and we found that the intrinsic oxidase activity of MnO2 NS doped with Fe3O4 NPs can be significantly enhanced. The chromogenic substrate TMB can be catalyzed by Fe3O4 @MnO2 NS to generate blue oxidized TMB, and UA can decompose the MnO2 NS to inhibit the color reaction of TMB selectively, thereby realizing the quantitative detection of UA. In addition, the UA biosensor can perform colorimetric analysis of UA level through three methods: naked eye, smartphone and ultraviolet-visible (UV-vis) spectrophotometer. The linear ranges of UV-vis spectrophotometry and colorimetry with smartphone were 1-70 µM and 200-650 µM, respectively, and the limits of detection (LOD) were 0.27 µM and 21 µM. The analysis results of human plasma samples showed that the method had good selectivity and practicability.

An "on-off" ratio photoluminescence sensor based on catalytically induced PET effect by Fe3O4 NPs for the determination of coumarin.

Herein, using Fe3O4 nanoparticles (Fe3O4 NPs) as a magnetic artificial peroxidase, an "on-off" ratiometric photoluminescence sensor with high-sensitivity and high-selectivity for coumarin was constructed based on photoinduced electron transfer (PET) between 7-hydroxycoumarin and rhodamine B (RB). The results showed that Fe3O4 NPs catalyzed H2O2 to generate nucleophilic group ·OH, which attacked the active site of coumarin and produced strong fluorescent 7-hydroxycoumarin molecules. Then, the fluorescence of RB was quenched with 7-hydroxycoumarin through the PET effect. The ratio signal generated in the above process was used for the quantitative detection of coumarin. Under optimized conditions, the linear range 0.5-25 mg/L was acquired for coumarin with the detection limit of 0.016 mg/L. This method had excellent selectivity and the recovery rate was 81.8%-106.8% with the relative standard deviation less than 5.6%, so it can be used for the quantitative analysis of coumarin in complex matrix samples.

Electrochemical Biosensor Based on HRP/Ti3C2/Nafion Film for Determination of Hydrogen Peroxide in Serum Samples of Patients with Acute Myocardial Infarction.

Hydrogen peroxide (H2O2) has been reported to mediate a variety of physiological and pathological processes in living systems. In this work, a biosensor for determination of H2O2 was prepared by using an HRP/Ti3C2/Nafion film-modified glassy carbon electrode (GCE). Ti3C2 nanosheets with remarkable conductivity and high specific surface area were chosen as carriers for HRP. Moreover, this biosensor modified with HRP has a specific catalytic effect on H2O2. The difference in peak current could reflect the quantitative change of H2O2. The linear range of the biosensor is 5-8000 µM, and the detection limit is 1 µM (S/N = 3). This biosensor was used to detect H2O2 in clinical serum samples of normal controls and patients with acute myocardial infarction (AMI) before and after percutaneous coronary intervention (PCI). The results showed that the difference between normal controls and patients is significant (P < 0.05), as well as the difference for patients before and after PCI (P < 0.01), but no significant difference existed between postoperative patients and normal controls. This biosensor has the advantages of simple preparation, high sensitivity, and quick detection, showing potential application in clinical diagnosis.

A CRISPR-derived biosensor for the sensitive detection of transcription factors based on the target-induced inhibition of Cas12a activation.

Transcription factors (TFs) are the key proteins for the decision of cell fates, and they have been recognized as potent markers for diagnostic and treatment of diseases. Herein, we report on a highly sensitive biosensor for the detection of TFs based on the CRISPR/Cas12a system. This biosensor was accomplished based on the competitive binding of the Cas12a-crRNA and TFs towards a dsDNA referred to as activator. Without TFs, the activator can be recognized by Cas12a-crRNA and cause the activation of the DNase activity of Cas12a. When TFs were added, the TFs can bind with the activator because the activator was designed to contain the specific binding sites of target TFs. We find that this binding can inhibit the association between Cas12a-crRNA and the activator, which hinders the activation of Cas12a. As a proof-of-concept, the rapid detection of five kinds of TFs was presented, and the detection was extended to the analysis of TFs expression in xenograft solid tumors from mice. This investigation is the first attempt to apply CRISPR technology in the sensing of TFs, and it discloses that the blocking of activator can be applied as a new sensing mechanism for the development of CRISPR-based biosensor.

A label-free electrochemical biosensor based on magnetic biocomposites with DNAzyme and hybridization chain reaction dual signal amplification for the determination of Pb2.

A highly sensitive and selective electrochemical biosensor for Pb2+ with a dual-amplification strategy is proposed. The first amplification step was realized by the cycle of Pb2+ and 8-17 DNAzyme (S2), and the hybridization chain reaction (HCR) triggered by S1 further amplified the electrochemical signal. Fe3O4@Au NPs, as a multifunctional magnetic carrier, is not only manifested in the construction of a magnetically controlled electrochemical response interface, but also has significant contribution in the purifying system, reducing interference, increasing the specific surface area, and the DNA loading. The magnetic nanocomposites were characterized by TEM as spheres with particle size of around 39 nm. When there was no Pb2+, long double-strand DNA (dsDNA) is formed on the surface of Fe3O4@Au NPs by the S1-triggered HCR; in the presence of Pb2+, S2 is activated and S1 on the surface of magnetic biocomposites (Fe3O4@Au NPs-S1) is continuously cleaved with the cycle of Pb2+ and S2, leading to a significant decrease of methylene blue (MB) absorbed on dsDNA. Such reverse dual-signal amplification strategy effectively increased the current difference and improved the sensitivity of the proposed sensor. The electrochemical signal of MB was obtained by differential pulse voltammetry (DPV) with preconcentration, showing a linear response toward Pb2+ ranging from 50 pM to 1 µM with a detection limit of 15 pM. The proposed method has feasible applications in detecting other heavy metal ions based on other metal-dependent DNAzyme. Graphical Abstract.

A label-free electrochemical magnetic aptasensor based on exonuclease III-assisted signal amplification for determination of carcinoembryonic antigen.

A novel label-free and exonuclease III (Exo III)-assisted signal amplification electrochemical aptasensor was constructed for the determination of carcinoembryonic antigen (CEA) via magnetic field-induced self-assembly of magnetic biocomposites (Fe3O4@Au NPs-S1-S2-S3). The magnetic biocomposites were acquired by modifying double-stranded DNA (S1-S2-S3) on the surface of Fe3O4@Au nanoparticles (Fe3O4@Au NPs). Among them, Fe3O4@Au NPs were used as carriers for magnetic separation, thiolated single-stranded DNA (S1) provided signal sequence, CEA aptamer (S2) worked as a recognition element, and complementary strand (S3) was used to form double strands. In the presence of CEA, S2 bonded with CEA competitively; the exposed S1 could not be cleaved since Exo III was inactive against ssDNA. The G-quadruplex/hemin complexes finally formed with the existence of K+, and the high electrochemical signal of G-quadruplex/hemin complexes was recorded by differential pulse voltammetry (DPV) at - 0.6 V. Conversely, in the absence of CEA, dsDNA was cleaved from the 3' blunt end by Exo III; the disappearance of G-rich sequence blocked the generation of the signal. This method exhibited good selectivity and sensitivity for the determination of CEA; the linear range was from 0.1 to 200 ng mL-1 and the limit of detection was 0.4 pg mL-1. Graphical abstract.

A signal transduction approach for multiplexed detection of transcription factors by integrating DNA nanotechnology, multi-channeled isothermal amplification, and chromatography.

The variation patterns of transcription factors (TFs) provide direct information for the states of cell populations, which is of significance for biomedical research and clinical diagnostics. Herein, we show that through multi-channeled isothermal amplification, it is feasible to connect DNA-based signal transduction with chromatography for multiplexed detection of TFs. The described system is referred to as "PAC" which includes three major steps: (i) Protection, which uses DNA-modified magnetic beads to capture TFs and converts the capturing event into triggering signal; (ii) Amplification, which receives the triggering signal and generate DNA reporters through multi-channeled extension and nicking of oligonucleotides; and (iii) Chromatography, which separates and detects the DNA reporters in liquid chromatography. The quantitative detection of five essential TFs includes p50, p53, AP-1, MITF, and c-Myc is realized in a multiplexed manner, with the lowest detection limit of 0.5 pM. PAC can also provide effective means to measure the above five TFs in real samples, including cultured cells, xenograft tumors, and blood-based liquid biopsy. This study not only established a solution for multiplexed measurement of TFs for molecular diagnostics, but also paved avenue for bridging the gap between DNA nanotechnology and chromatography.

Dual-Emission Reverse Change Ratio Photoluminescence Sensor Based on a Probe of Nitrogen-Doped Ti3C2 Quantum Dots@DAP to Detect H2O2 and Xanthine.

Titanium carbide quantum dots (Ti3C2 QDs) derived from two-dimensional (2D) Ti3C2Tx (MXene) are the rising-star material recently. Herein, nitrogen-doped Ti3C2 QDs (N-Ti3C2 QDs) were synthesized via a solvothermal method. The obtained N-Ti3C2 QDs exhibited excitation-dependent photoluminescence, antiphotobleaching, and dispersion stability. Furthermore, by combining the N-Ti3C2 QDs and DAP (2,3-diaminophenazine, the oxidative product of o-phenylenediamine) as a composite nanoprobe (N-Ti3C2 QDs@DAP), we developed a dual-emission reverse change ratiometric sensor to quantitatively monitor H2O2 based on photoinduced electron-transfer effects, where N-Ti3C2 QDs acted as the donor and DAP as the acceptor. On the basis of the xanthine converting into H2O2 through the catalysis of xanthine oxidase, the N-Ti3C2 QDs@DAP nanoprobe was also exploited for xanthine sensing. As a result, the proposed assay was demonstrated to be highly sensitive for H2O2 and xanthine with detection limits of 0.57 and 0.34 µM, respectively. In a word, we have investigated the application of N-Ti3C2 QDs in H2O2 and xanthine sensing and opened a new and exciting avenue for the N-Ti3C2 QDs in biosensing.

An electrochemical and fluorescence dual-signal assay based on Fe3O4@MnO2 and N-doped carbon dots for determination of hydrogen peroxide.

A novel electrochemical and fluorescence dual-signal assay was developed for the determination of hydrogen peroxide (H2O2) based on Fe3O4@MnO2 and N-doped carbon dots (NCDs). Fe3O4@MnO2 was not only applied as the recognizer for H2O2 but also served as the fluorescence quencher and electrochemical enhancer. This permits the dual-signal readout of the analytical system. In the absence of H2O2, the NCDs were quenched by Fe3O4@MnO2, and the oxidation of the electrochemical probe ferrocene (Fc) was catalyzed by Fe3O4@MnO2. In the presence of H2O2, MnO2 was reduced to Mn2+, leading to the fluorescence recovery of NCDs and the reduction in the oxidation signal of Fc. By combining the electrochemical method and the fluorescence assay, more comprehensive and valuable information for H2O2 determination was provided to meet different analytical demands. The method exhibits good repeatability and selectivity with a detection limit of 1.0 µM for the fluorescence assay and 0.6 µM for the electrochemical method. The proposed approach holds great potential for probing released targets from living cells. Graphical abstract.

Label-Free Colorimetric Detection of Acid Phosphatase and Screening of Its Inhibitors Based on Biomimetic Oxidase Activity of MnO2 Nanosheets.

In this research, we attempted to develop a sensitive colorimetric sensing strategy for the detection of acid phosphatase (ACP) based on MnO2 nanosheets and explored its applications in screening and evaluating inhibitors of ACP. The MnO2 nanosheets exhibit intrinsic biomimetic oxidase activity, which can catalyze the oxidation of the colorless 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonate) diammonium salt (ABTS) into green oxidized ABTS (oxABTS). Upon the introduction of ACP, l-ascorbic acid-2-phosphate can be dephosphorylated to ascorbic acid, which arouses the disintegration of MnO2 nanosheets into Mn2+ ions. This disintegration weakens the enzyme mimicking activity of the MnO2 nanosheets, leading to the impediment of the oxidation of ABTS. Conversely, in the absence of ACP, the ABTS is rapidly oxidized by MnO2, leading to a significant colorimetric signal change. The absorbance difference at 420 nm displayed a linear relationship with the concentration of ACP ranging from 0.075 to 0.45 mU·mL-1, generating a detection limit of 0.046 mU·mL-1. In the inhibition assays, this sensing platform provided simple detection for parathion-methyl (PM), a representative inhibitor of ACP. The facile evaluation of the inhibitory effect of PM, including its IC50 toward ACP, was also realized.

A versatile fluorometric aptasensing scheme based on the use of a hybrid material composed of polypyrrole nanoparticles and DNA-silver nanoclusters: application to the determination of adenosine, thrombin, or interferon-gamma.

The authors describe a versatile aptasensing scheme based on the use of polypyrrole nanoparticles (PPyNPs) and DNA-silver nanoclusters (DNA-AgNCs) for multiple target detection. The DNA-AgNCs consist of two functional domains, viz. (a) a nucleation domain for attaching the metal core of the nanoclusters, and (b) a recognition domain which consists of a single-stranded aptamer. In the absence of analytes, the single-strand recognition domain will be absorbed onto the surface of the PPyNPs through π stacking and hydrophobic interactions. As a result, the red fluorescence of the DNA-AgNCs (with excitation/emission peaks at 535/625 nm) is quenched by the PPyNPs. On introducing the analytes, the DNA-AgNCs will bind them. This leads to the desorption of DNA-AgNCs and the recovery of the red fluorescence. Based on the above strategy, a versatile, sensitive and selective aptasensor was established for detection of adenosine, thrombin and interferon-gamma. The method was applied to the detection of the above targets in (spiked) serum samples and gave satisfactory results, with detection limit of 0.58 nM for IFN-γ, 0.39 nM for adenosine, and 2.2 nM for thrombin. The use of PPyNPs results in uniquely low non-specific absorption and in improved analytical results in case of real-sample analysis when compared to previously reported methods. Graphical abstract Schematic illustration of DNA-silver nanoclusters and polypyrrole nanoparticles in an aptasensor for detection of multiple targets.

Combined Amperometry and Electrochemical Cytometry Reveal Differential Effects of Cocaine and Methylphenidate on Exocytosis and the Fraction of Chemical Release.

Amperometry with nanotip electrodes has been applied to show cocaine and methylphenidate not only trigger declines in vesicle content and exocytotic catecholamine release in a model cell line but also differentially change the fraction of transmitter released from each individual vesicle. In addition, cocaine accelerates exocytotic release dynamics while they remain unchanged after methylphenidate treatment. The parameters from pre-spike feet for the two drugs are also in opposition, suggesting this aspect of release is affected differentially. As cocaine and methylphenidate are psychostimulants with similar pharmacologic action but have opposite effects on cognition, these results might provide a missing link between the regulation of exocytosis and vesicles and the effect of this regulation on cognition, learning, and memory. A speculative chemical mechanism of the effect of these drugs on vesicle content and exocytosis is presented.