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Covalent organic frameworks (COFs) are gaining growing interest owing to their various structures and versatility. Since their specific physical–chemical characteristics endow them great usage potentiality in biosensing, we herein have synthesized spherical COFs with regular shape and good dispersion, which are further used for the design of a novel nanoprobe by modifying Histostar on the surface of the COFs. Moreover, we have applied a nanoprobe for the fabrication of an electrochemical biosensor to detect exosomes. Since Histostar is a special polymer, conjugated with many secondary antibodies (IgG), and HRP can increase the availability of HRP at the antigenic site, the biosensor can have a strong signal amplification ability. Meanwhile, since COFs with high porosity can be loaded with a huge amount of Histostar, the sensitivity of the biosensor can be further improved. With such a design, the proposed biosensor can achieve a low exosomes detection limit of 318 particles/µL, and a wide linear detection range from 103 particles/µL to 108 particles/µL. So, this work may offer a promising platform for the ultrasensitive detection of exosomes. [ABSTRACT FROM AUTHOR]

A novel electrochemiluminescence (ECL) biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide (AgNCs@MoS2) as an ECL material, peroxodisulfate (S2O82−) as a co-reactant, and semicarbazide (Sem) as a co-reaction accelerator. Firstly, hairpin probe Ha modified on AgNCs@MoS2/GCE was unfolded based on its hybridization with target microRNA. Then, the unfolded Ha can further be hybridized with another hairpin DNA of Hb on (AuNPs-semicarbazide)@Cu-MOF, resulting in the release of target microRNA, which further causes a cyclic hybridization. This creates more (AuNPs-semicarbazide)@Cu-MOF on the electrode surface, achieving cyclic hybridization signal amplification. Strikingly, due to the presence of Sem, accelerating the reduction of S2O82− and resulting in the generation of more oxidant intermediates of SO42−, the amount of excited states of Agincreases to further amplify the ECL signal. The biosensor exhibited high sensitivity with a low LOD of 1.067 fM, indicating that the introduction of co-reaction accelerators can provide an effective method for signal amplification. The applicability of this method was assessed by investigating the effect of Pb(II) ion on miRNA-162a expression level in maize seedling leaves. [ABSTRACT FROM AUTHOR]

MicroRNAs play crucial role in regulating gene expression in organism, thus it is very necessary to exploit an efficient method for the sensitive and specific detection of microRNA. Herein, a signal-on electrochemiluminescence biosensor was fabricated for microRNA-319a detection based on two-stage isothermal strand-displacement polymerase reaction (ISDPR). In the presence of target microRNA, amounts of trigger DNA could be generated by the first ISDPR. Then, the trigger DNA and the primer hybridized simultaneously with the hairpin probe to open the stem of the probe, and then the ECL signal will be emitted. In the presence of phi29 DNA polymerase and dNTPs, the trigger DNA could be displaced to initiate a new cycle which was the second ISDPR. Due to the two-stage amplification, this method presented excellent detection sensitivity with a low detection limit of 0.14 fM. Moreover, the applicability of the developed method was demonstrated by detecting the change of microRNA-319a content in the leaves of rice seedlings after the rice seeds were incubated with chemical mutagen of ethyl methanesulfonate. [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]

A photoelectrochemical biosensor is described for sensitive detection of microRNA-162a. A multiple amplification strategy is employed that involves (a) isothermal strand displacement polymerase reaction; (b) terminal deoxynucleotidyl transferase-mediated extension, (c) amplification of streptavidin-coated gold nanoparticles, and (d) biotin functionalized alkaline phosphatase. Graphite-like C3N4 (g-C3N4) nanosheets were used as photoactive material. By using these amplification strategies, the detection limit is as low as 0.18 fM of microRNA, and the photocurrent increases linearly with the concentration of microRNA-162a in the range from 0.5 fM to 1 pM. The method was successfully applied to quantify the expression level of microRNA-162a in total RNA extracted from the leaves of maize seedlings after incubation with the chemical mutagen ethyl methanesulfonate. The results confirmed the applicability of the method to the analysis of practical biological samples.Schematic of a photoelectrochemical microRNA assay based on a multiple amplification strategy involving (a) isothermal strand displacement polymerase reaction; (b) terminal deoxynucleotidyl transferase-mediated extension, (c) amplification of streptavidin-coated gold nanoparticles, and (d) biotin functionalized alkaline phosphatase. [ABSTRACT FROM AUTHOR]

[Display omitted] • SARS-CoV-2 PLpro as a new biomarker is used to diagnose COVID-19. • A novel PLpro-activated peptide-DNA smart nanoprobe is designed for sensitive and specific detection of SARS-CoV-2. • The fabricated biosensor can be used for the detection of SARS-CoV-2 in blood, saliva, and clinical samples. • The biosensor can be used to screen and validate inhibitors of SARS-CoV-2 PLpro. The persistent coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is still infecting hundreds of thousands of people every day. Enriching the kits for SARS-CoV-2 detection and developing the drugs for patient treatments are still urgently needed for combating the spreading virus, especially after the emergence of various mutants. Herein, an electrochemical biosensor has been fabricated in this work for the detection of SARS-CoV-2 via its papain-like cysteine protease (PLpro) and the screening of protease inhibitor against SARS-CoV-2 by using our designed chimeric peptide-DNA (pDNA) nanoprobes. Utilizing this biosensor, the sensitive and specific detection of SARS-CoV-2 PLpro can be conducted in complex real environments including blood and saliva. Five positive and five negative patient throat swab samples have also been tested to verify the practical application capability of the biosensor. Moreover, we have obtained a detection limit of 27.18 fM and a linear detection range from 1 pg mL−1 to 10 μg mL−1 (I = 1.63 + 4.44 lgC). Meanwhile, rapid inhibitor screening against SARS-CoV-2 PLpro can be also obtained. Therefore, this electrochemical biosensor has the great potential for COVID-19 combating and drug development. [ABSTRACT FROM AUTHOR]

• Covalent organic frameworks conjugated with DNA and horseradish peroxidase (HRP-DNA-COFs, HDCs) are successfully prepared. • The prepared HDCs can recognize exosomes and catalyze the oxidation of 1, 3, 5-trimethylbenzene (TMB) substrate. • An HDCs-based electrochemical biosensor is constructed for exosome detection. • The HDCs-based biosensor achieves good performance to detect exosomes with simplicity and sensitivity. Quantification of trace exosomes in biofluids is helpful for the early diagnosis of cancers. Electrochemical biosensors have attracted special attentions for exosome detection, while the employment of nanoconjugates in the construction of electrochemical biosensors can achieve better performance. So, in this work, we have designed and fabricated HRP-DNA-COF nanoconjugates (HDCs) that involve covalent organic frameworks (COFs) as the scaffold, cholesterol-tagged DNA to recognize exosomes and horseradish peroxidase (HRP) to amplify the signal readout. The successful preparation of HDCs have been verified experimentally, based on which an electrochemical biosensor has been constructed for exosome detection. Attributed to the specific recognition ability and excellent catalytic ability of HDCs, the biosensor achieves good performance to detect exosomes with simplicity and sensitivity in the linear range from 104 to 107 particles/μL. Besides, the strategy proposed in this work to construct COF-based nanoconjugates may promote the wider application of COFs in biomedical research. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydroquinone-mediated OPECT biosensing strategy was developed. • ZnSe/Bi 2 MoO 6 heterojunction was employed as photoactive material. • Sensitive and selective detection of FTO protein was achieved. • Hemin catalyzed the oxidation of ZnSe and hydroquinone by H 2 O 2 was employed to achieve signal suppression. • Rhein and perfluorohexane sulfonate inhibited FTO protein activity. Organic photoelectrochemical transistor (OPECT) biosensing is a new concept that combines photoelectrochemical and organic electrochemical transistor biosensing. It reduces background noise and combines both signal amplification for low abundance biomolecule detection. In this work, an OPECT biosensor for the detection of fat mass and obesity-associated protein (FTO) was constructed, in which ZnSe/Bi 2 MoO 6 was chosen as the gate material, hm6ARNA (containing N6-methyladenine RNA sequence) as the target molecule, and hydroquinone as the electron donor. Under FTO oxidation induced RNA demethylation, the formation of hemin loaded with G-quadruplex on the electrode surface was triggered. With the catalysis of hemin-based DNAzyme towards the oxidation reaction caused by H 2 O 2 towards hydroquinone and ZnSe, the electron donor was consumed and ZnSe was oxidized in situ to form SeO 2 which reduced the photo-anodic response. The variation of the gate effectively gated the state of the channel polymer thus producing different channel current responses, a process that was closely related to the content of FTO. In addition, the effects of rhein and potassium perfluorohexanesulfonate on FTO activity were also investigated in this experiment, with IC 50 values of 10.62 μM, 31.28 mg/L respectively. [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]

N 6 -methyladenosine (m 6 A) is an enigmatic and abundant internal modification in eukaryotic messenger RNA (mRNA), which could affect various aspects of RNA metabolism and mRNA translation. Herein, a novel photoelectrochemical (PEC) immunosensor was constructed for m 6 A detection based on the inhibition of Cu 2+ to the photoactivity of g-C 3 N 4 /CdS quantum dots (g-C 3 N 4 /CdS) heterojunction, where g-C 3 N 4 /CdS heterojunction was used as photoactive material, anti-m 6 A antibody as recognition unit for m 6 A-containing RNA, Phos-tag-biotin as link unit and avidin functionalized CuO as PEC signal indicator. When CuO was captured on electrode through biotin-avidin affinity reaction and then treated with HCl, Cu 2+ could be released and Cu x S would be formed based on the selective interaction between CdS and Cu 2+ , leading the photocurrent obviously decreased. Under the optimal detection conditions, the PEC biosensor displayed a linear range of 0.01–10 nM and a low detection limit of 3.53 pM for methylated RNA determination. Furthermore, the developed method could also be used to detect the expression level of m 6 A methylated RNA in serum samples of breast cancer patient before and after operative treatment. The proposed assay strategy has a great potential for detecting the expression methylation level of RNA in real sample. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are an emerging type of porous crystalline polymers that are built by light elements (typically H, B, C, N, O and Si) via organic covalent bonds. Currently, COFs have been exploited for biomedical application due to their unique properties, such as structural diversity, intrinsic stability, ordered porosity, tailor-made functions, and excellent adsorption features. In particular, COFs are increasingly popular in the construction of biosensors for the detection of various disease biomarkers, and have been extended to the clinical applicability for early diagnostics, medication instruction and prognostic monitoring of diseases. In this review, we mainly summarize the recent advances on COFs-based biosensors for the assay of disease biomarkers with clinical applications. According to the features of molecular structure, disease biomarkers are classified into four categories, including small biological ions/molecules, proteins, nucleic acids, and cancer cells/exosomes. Impressively, COFs-based biosensors present a bright prospect in clinical diagnosis of diseases in both hospital-end and household-end utilization. • Progress on COFs-based biosensors for the assay of disease biomarkers is summarized. • Four categories of disease biomarkers are mainly discussed with the clinical applications. • COFs-based biosensors exhibit excellent sensitivity and anti-interference in diseases diagnosis. • The challenges of COFs-based biosensors are also put forward. [ABSTRACT FROM AUTHOR]