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Some biological small molecules such as hydrogen sulfide (H 2 S) and hypochlorous acid (HClO), play pivotal roles in numerous biological and pathological processes and are associated with various diseases. The detection and monitoring them is of continued research interest. Here we report a sequential detection mode fluorescence probes that allow for the sensing of HS– and ClO–. The mixture of P and HS– constructs a specific sensing system S for ClO–. The substitution product S is stable in air, which also could be used independently. Mechanism studies demonstrate that HS– substitutes the Cl atom in P. Furthermore, the addition of ClO– facilitates a ring-forming reaction, resulting in the formation of a thiofuran ring within the product (T). Interestingly, P has a highly ordered steric packing and could self-assemble into a rice-spike-like structure. Upon the addition of HS–, the assemblies decompose into free molecules. After interaction with ClO–, these molecules further transform to T with strong assembled capacity, featuring a larger number of nanosheets. This study provides a novel mechanism for sensing HS– and ClO–, cell and living animal imaging further indicating the good application prospects of these probes in biosensing and bioimaging. [Display omitted] • Three fluorescent probes for detection HS– and ClO– in sequence were developed. • The responsiveness to ClO– is based on the thiofuran ring-forming reaction. • The self-assembly may play positive roles in the detection of HS– and ClO–. • These probes were applied as HS− and ClO− imaging in living cells and mice. [ABSTRACT FROM AUTHOR]

Programmed death-ligand 1 protein positive (PD-L1+) exosome is one of the most prospective biomarkers for the diagnosis of cancer. However, the current methods for the detection of PD-L1+ exosomes are usually laborious, time-consuming and require numerous samples. Herein, we report in this paper an electrochemical biosensor for PD-L1+ exosomes detection based on ultra-thin two-dimensional covalent organic framework nanosheets (2D COF NSs) coupled with clustered regularly interspaced short palindromic repeats (CRISPR) Cas 12a for signal amplification. Firstly, COF-367 NSs functionalized with gold nanoparticles (AuNPs) have been synthesized for the modification of the working electrode, thus the proposed sensor can show highly improved electrochemical performance. Secondly, by utilizing the trans-cleavage activity of Cas12a, this sensor can achieve very high sensitivity for the detection of PD-L1+ exosomes. With such design, the biosensor can have a linear range from 1.2 × 102 to 1.2 × 107 particles/μL with a detection limit of 38 particles/μL. Moreover, this sensor can be employed to analyze non-small cell lung cancer (NSCLC) patient serum samples, and successfully identify NSCLC patients, demonstrating the great potential in clinical applications. [Display omitted] • An ultra-thin 2D COF NSs-based biosensor was designed. • It can exhibit excellent analytical performance for the detection of PD-L1+ exosomes. • The low detection limits of 38 particles/μL was achieved. • The proposed method has been used to analyze the clinical serum samples. [ABSTRACT FROM AUTHOR]

Abstract: This work described a highly sensitive amperometric biosensor for organophosphates (OPs) pesticides based on immobilization of acetylcholinesterase (AChE) on multiwall carbon nanotubes (MWCNTs)-β-cyclodextrin (β-CD) composite modified glassy carbon electrode. The synthesized composite through polymer wrapping strategy has been characterized by attenuated total reflection Fourier-transform infrared spectra (ATR-FTIR) measurement and scanning electron microscopy (SEM) images. Due to the good dispersibility and porous structures of MWCNTs-β-CD composite, the resulting surface provided a favorable microenvironment for acetylcholinesterase biosensor fabrication and maintained the bioactivity of AChE for screening of OPs exposure. MWCNTs promoted electron-transfer reactions at a lower potential and catalyzed the electro-oxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of OPs on the AChE activity, using dimethoate as a model compound, the inhibition of dimethoate was proportional to its concentration ranging from 0.01 to 2.44 and 2.44 to 10.00μM, with a detection limit was 2nM (S/N=3). The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors. [Copyright &y& Elsevier]

Abstract: A facile, one-step synthesis of nanocomposites using multiwalled carbon nanotube coating gold nanoparticles (MWCNTs-Au) was presented. Scanning electron microscopy and UV–vis spectroscopy confirmed that more than 97% of gold nanoparticles have been loaded on the surface of carbon nanotubes without congregation. The formed MWCNTs-Au nanocomposites offered an extremely hydrophilic surface for biomolecule adhesion, leading to a stable acetylcholinesterase (AChE) biosensor. Due to the excellent conductivity of the nanocomposites, the immobilized AChE showed favorable affinity to acetylthiocholine (ATCl) and could catalyze the hydrolysis of ATCl with a value of 268μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition of organophosphates (OPs) on the enzymatic activity of AChE, the magnitude of peak current from thiocholine on the biosensor is a simple and effective way to biomonitoring of OPs exposure. Using malathion as a model compound, the inhibition of malathion was proportional to its concentration ranging from 1.0 to 1000ngmL−1 and from 2 to 15μgmL−1, with a detection limit 0.6ngmL−1. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors. [Copyright &y& Elsevier]

Intracellular pH has been associated with multiple biological processes. However, fluorescent probes for pH are limited. Herein, a new pH fluorescent probe was developed based on reversible structural changes. This probe provided three reversible pH response modes within 2.00–12.00. Under the acidic conditions, there is no-fluorescence, under the neutral conditions, the emission is at 650 nm, under the alkaline conditions, the emissions at 650 nm decreases and at 460 nm appears and increases simultaneously. The probe solution presented distinct colors response to the pH values from 2.00 to 12.00. The fluorescent response from pH 2.00–12.00 makes the probe suitable for the monitoring pH in living cells. Moreover, the imaging results confirm that probe S can be applied in fluorescence imaging in living cells. • A new pH fluorescent probe was developed based on reversible structural changes. • The probe provided three reversible pH response modes accompanied by different color changes. • The probe can be applied to live cell pH monitoring and lysosome imaging. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Electrochemiluminescence biosensor was fabricated for 5-methylcytosine and TET 1 protein detection. • β-Glucosyltransferase activities was also detected by this biosensor. • The Biosensor was based on quenching effect of Au nanoclusters by H 2 O 2 interactions. • The assay exhibited excellent stability, reproducibility and selectivity. • This biosensor can be used to screen TET 1 and β-glucosyltransferase inhibitors. Abstract 5-Methylcytosine (5 mC) is considered to play a key regulating role in gene transcription and can be oxidized by ten–eleven translocation (TET) dioxygenases to 5-hydroxymethylcytosine (5 hmC). In order to better understand the function of 5 mC in gene transcription and the mechanism of demethylation, sensitive and selective methods must be developed for detecting 5 mC, the TET 1 protein and T4 β-glucosyltransferase (β-GT). In this work, a novel electrochemiluminescence (ECL) biosensor was fabricated for the quantification of 5 mC, TET 1 protein and β-GT activities, as well as inhibitor screening, based on the interaction of chemically excited gold nanoclusters (AuNCs) with H 2 O 2. The ECL biosensor was constructed on an Au nanoparticle (AuNP) decorated glassy carbon electrode, to which BSA coated AuNCs and thiol-containing probe DNA was subsequently attached. Hybridization with target 5 mC-DNA, was followed by demethylation by TET 1 and glycosylation by β-GT. After reaction of the glycosyl group with 4-carboxyphenylboronic acid, horseradish-peroxidase was then grafted to the DNA backbone to catalyze H 2 O 2 reduction and the oxidation of hydroquinone to benzoquinone. The ECL of the chemically excited AuNCs was attenuated in the presence of H 2 O 2 , with more H 2 O 2 being decomposed in the presence of 5 mC DNA, TET-1 or β-GT, leading to an enhanced ECL response. The proposed assay demonstrated high selectivity for 5 mC-DNA detection in the concentration range 0.01 nM–50 nM, with a detection limit of 3.46 pM. The applicability of this biosensor was confirmed by the evaluation of blood serum, with the developed biosensor having great potential in drug discovery. [ABSTRACT FROM AUTHOR]

MicroRNAs play a crucial role in regulating plant growth, such as involving in the pathways of phytohormons signaling, which function in broad range of important aspects in many stages of plant development and evolution. To figure out the components part of microRNA in phytohormone signaling network, a sensitive photoelectrochemical biosensor was developed to detect miRNA-319a specifically using CuO-CuWO 4 as photoactive material and in situ generation electron donor technique. Taking the advantage of rolling circle amplification, nicking endonuclease triggered exponential amplification of target molecule, specific interaction between phosphate group and phos-tag and between biotin and avidin, the developed strategy can greatly amplify the detection signal only using trace amount of target miRNA-319a. The wide linear range was obtained from 1 fM to 0.1 nM and the detection limit was estimated to be 0.47 fM (S/N = 3). The developed method also showed good detection specificity. The effect of five phytohormones on the expression level of miRNA-319a in rice leaves was also investigated. This will be a basal principle of investigating the signaling network of phytohormones. [ABSTRACT FROM AUTHOR]