Search

The increasing uranium containing wastes generated during uranium mining and finishing pose a huge threat to the environment and human health, and thus robust strategies for on-site monitoring of uranium pollutant are of great significance for environmental protection around uranium tailings. Herein, a facile "turn-on" colorimetric platform that can achieve uranium detection by spectrometry and naked eyes was developed based on the uranium-enhanced nanozyme activity of covalent organic framework (JUC-505). Thanks to the extended π-conjugated skeleton and donor-acceptor (D-A) structure, JUC-505 exhibited superior photo-activated nanozyme activity, which would be prohibited when the cyano group in JUC-505 skeleton was transformed to the amidoxime group. Further results elucidated that the coordination of uranium with amidoxime groups led to the electron transfer between uranium and the JUC-505-AO skeleton, and thus significantly restored the nanozymatic activity of JUC-505-AO with the subsequent remarkable color changes. Moreover, the uranium concentrations in uranium tailing wastewater detected by the present "turn-on" colorimetric method were well agreed with those by ICP-MS, demonstrating a high accuracy of the present method in real samples. The D-A structured JUC-505 with superior photocatalytic property and nanozymatic activity was applied to facilitate colorimetric detection of uranium, which displays the advantages of low detection limit, excellent selectivity, fast response and simple operation for uranium detection in real samples, and shows a great potential in on-site monitoring of uranium pollutant around uranium tailings as well as nuclear power plant. [Display omitted] • A facile "turn-on" colorimetric platform was developed for on-site uranium detection by the nanozymatic activity of JUC-505. [ABSTRACT FROM AUTHOR]

DNA-modifying enzymes act as critical regulators in a wide range of genetic functions (e.g., DNA damage & repair, DNA replication), and their aberrant expression may interfere with regular genetic functions and induce various malignant diseases including cancers. DNA-modifying enzymes have emerged as the potential biomarkers in early diagnosis of diseases and new therapeutic targets in genomic research. Consequently, the development of highly specific and sensitive biosensors for the detection of DNA-modifying enzymes is of great importance for basic biomedical research, disease diagnosis, and drug discovery. Single-molecule fluorescence detection has been widely implemented in the field of molecular diagnosis due to its simplicity, high sensitivity, visualization capability, and low sample consumption. In this paper, we summarize the recent advances in single-molecule counting-based biosensors for DNA-modifying enzyme (i.e, alkaline phosphatase, DNA methyltransferase, DNA glycosylase, flap endonuclease 1, and telomerase) assays in the past four years (2019 − 2023). We highlight the principles and applications of these biosensors, and give new insight into the future challenges and perspectives in the development of single-molecule counting-based biosensors. [Display omitted] • We review single-molecule counting-based biosensors for DNA-modifying enzyme detection. • The principles and applications of these biosensors are highlighted. • The performances of different biosensors are compared. • We discuss the future challenges and perspectives in this field. [ABSTRACT FROM AUTHOR]

Stimulus-responsive double-ligand luminol-Eu-IPA infinite coordination polymer nanoparticles (luminol-Eu-IPA CPNPs) were prepared as a ratiometric fluorescence probe for highly selective detecting Hg2+. The CPNPs were constituted of Eu3+ as the nuclear metal coordinated by isophthalic acid (IPA) together with luminol as an auxiliary ligand. The photoinduced electron transfer (PET) occurring from IPA to luminol prevented the antenna effect between IPA and Eu3+, leading to the quench fluorescence of Eu3+ under light excitation. As Hg2+ has a high affinity to N atom of luminol and the spin-orbit coupling effect, spectroscopically and magnetically silent properties, the fluorescence intensity of luminol was quenched. Meanwhile, the PET effect between luminol and IPA was interrupted under the presence of Hg2+. This process resulted in a significant decrease in the fluorescence intensity of luminol and a significant increase in the fluorescence intensity of Eu3+. Therefore, the fluorescence ratiometric detection of Hg2+ was performed by monitoring the ratio of the fluorescence at 617 nm of Eu3+ to that at 430 nm of luminol. The linear range was from 0.05 to 20 μM with a detection limit as low as 13.2 nM Hg2+ (S/N = 3). Due to the fluorescence of luminol be quenched and the effect of PET be disrupted simultaneously, the probe exhibiting excellent detection selectively can avoid false positive signals, which was demonstrated for monitoring mercury ions in real water samples. Precision in positioning ligands in CPNPs is an advantage to achieve high specificity in comparison to traditional organic dendrimers or precious metal nanomaterials. Image 1 • An effective lanthanide ratiometric fluorescent probe for Hg2+ based on luminol-Eu-IPA CPNPs has been demonstrated. • The photoinduced electron transfer occurring from luminol to IPA prevents the antenna effect between IPA and Eu3+. • The fluorescence of luminol is quenched and the effect of PET is disrupted simultaneously under the presence of Hg2+. • The ratiometric probe exhibiting excellent detection selectively can avoid false positive signals. [ABSTRACT FROM AUTHOR]

Telomerase, as a potential biomarker for early cancer diagnostics and therapies, has attracted considerable interests concerning its detection and monitoring. Herein, we develop a novel method for sensitive detection of telomerase activity by designing a gold nanoparticles/graphene oxide (AuNPs/GO) probe. The AuNPs were functionalized with a telomerase substrate (TS) primer and a 6-carboxy-fluorescein (FAM)-modified complementary DNA (P1). In the absence of telomerase, P1 exists in the random-coiled conformation, and the fluorescence resonance energy transfer (FRET) from FAM to AuNPs and GO results in efficient fluorescence quenching. In the presence of telomerase, the multiple hybridization between TS extension products and P1 leads to the conformation transition of P1 from single-stranded DNA to double-stranded rigid structure, and thus the FRET process can be prevented with the efficient fluorescence recovery. The metal enhanced fluorescence (MEF) effect between FAM and AuNPs can further effectively enhance the fluorescence of FAM, and thus the sensitivity and specificity of telomerase detection can be remarkably improved. It is worth mentioning that the proposed strategy does not need to design complex hairpin structure and allows the measurement of telomerase activity in three crude cell extracts equivalent to 7 HeLa cells, 8 A549 cells and 8 L929 cells in 1 h. In addition, the present sensing platform can be applied to inhibitor screening, in situ telomerase imaging, and intracellular drug delivery. Image 1 • The metal enhanced fluorescence effect can be regulated to generate significant fluorescence enhancement. • Weak background fluorescence can be realized via efficient fluorescence resonance energy transfer. • Telomerase activity down to 7 HeLa cells can be sensitively detected. • The method facilitates cellular imaging, inhibitor screening and drug delivery. [ABSTRACT FROM AUTHOR]

The METTL3/14 complex is an important RNA N6-Methyladenosine (m6A) methyltransferase in organisms, and the abnormal METTL3/14 complex activity is associated with the pathogenesis and various cancers. Sensitive detection of METTL3/14 complex is essential to tumor pathogenesis study, cancer diagnosis, and anti-cancer drug discovery. However, traditional methods for METTL3/14 complex assay suffer from poor specificity, costly antibodies, unstable RNA substrates, and low sensitivity. Herein, we construct a single quantum dot (QD)-based förster resonance energy transfer (FRET) biosensor for sensitive detection of METTL3/14 complex activity. In the presence of METTL3/14 complex, it catalyzes the methylation of adenine in the substrate probe, leading to the formation of m6A that protects the substrate probes from MazF-mediated cleavage. The hybridization of methylated DNA substrate with biotinylated capture probe initiates polymerization reaction to obtain a biotinylated double-stranded DNA (dsDNA) with the incorporation of numerous Cy5 fluorophores. Subsequently, the Cy5-incorporated dsDNA can self-assembly onto the 605QD surface to form the 605QD-dsDNA-Cy5 nanostructure, causing FRET between 605QD donor and Cy5 acceptor. This biosensor has excellent sensitivity with a limit of detection (LOD) of 3.11 × 10−17 M, and it can measure the METTL3/14 complex activity in a single cell. Moreover, this biosensor can be used to evaluate the METTL3/14 complex kinetic parameters and screen potential inhibitors. Furthermore, it can differentiate the METTL3/14 complex expression in healthy human tissues and breast cancer patient tissues, providing a powerful tool for cancer pathogenesis study, clinical diagnosis, prognosis monitoring, and drug discovery. We develop a single quantum dot-based förster resonance energy transfer (FRET) biosensor for sensitive detection of METTL3/14 complex activity in breast cancer tissues. [Display omitted] • We develop a single quantum dot-based FRET biosensor. • This biosensor can sensitively detect the METTL3/14 complex activity. • It can measure the METTL3/14 complex activity in a single cell. • This biosensor can evaluate kinetic parameters and screen inhibitors. • It can discriminate breast cancer patient tissues from healthy tissues. [ABSTRACT FROM AUTHOR]

Construction of covalent organic frameworks (COFs)-based nanozymes is of great importance for the extensive applications in catalysis and sensing fields. In this work, a two-dimensional COF (DAFB-DCTP COF) was fabricated via Knoevenagel condensation reaction. The integration of catalytically active sites of pyridine groups into the donor-acceptor (D-A) conjugated skeleton endows DAFB-DCTP COF with both hydrolytic and photosensitive properties. The DAFB-DCTP COF can be utilized as an artificial enzyme with selective and photo-enhanced catalytic efficiency, facilitating its application in photocatalytic degradation of hydrolase substrates (p- nitrophenyl acetate, p NPA) by nucleophilic reaction and further realizing colorimetric detection of the nanozyme inhibitor of organophosphorus nerve agent (diethyl cyanophosphonate, DCNP). The distinct color changes could be distinguished by naked eyes even at a low DCNP concentration, and the versatile smartphone analysis featured with reliability and simplicity. For the first time, the COFs' intrinsic hydrolase activity depending on their structural characteristics was investigated in synergy with the photosensitive performance originating from their photoelectric features. The present contribution provides a promising direction towards construction of colorimetric sensing platform based on the regulation of COFs' non-oxidoreductase activity under visible light irradiation. A novel photosensitive and hydrolytically active covalent organic framework (DAFB-DCTP COF) is constructed, which can be utilized as an artificial enzyme for photocatalytic degradation of ester substrates via nucleophilic reaction, and thus colorimetric detection of the organophosphorus nerve agent can be realized due to its inhibition effect on the mimic hydrolase activity and the photosensitive property of DAFB-DCTP COF. [Display omitted] • A D-A conjugated COF with pyridine groups is successfully constructed. • The COF nanozyme involves selective and photo-enhanced hydrolase activities. • Organophosphorus nerve agents can inhibit the nanoenzymatic activity of the COF. • Nerve agents can be colorimetrically detected by naked eyes or versatile smartphones. [ABSTRACT FROM AUTHOR]

In this work, a newly developed surface plasma resonance (SPR) system for the sensitive detection of M.SssI activity has been designed based on double signal amplification with DNA chain cyclic reactions and AuNPs. In the absence of M.SssI, hairpin DNA 1 (HP1) can be cleaved into s1 fragments catalyzed by HpaII. The s1 fragments can then trigger a recycling process of hairpin DNA 2 (HP2) hybridization and subsequently release massive s2 and s3 in the solution of Nt.AlwI and HPII. AuNPs-DNA can be captured on gold film by the released s2 and s3 to produce a strong SPR signal. Whereas in the presence of M.SssI, methylated HP1 cannot be cleaved by HpaII, thus produce a weak SPR signal. The SPR signals are dependent on the M.SssI concentration in the range from 0.5 to 50 U/mL. The successful detection of M.SssI activity in clinical serum samples and inhibition of M.SssI using 5-Aza and 5-Aza-dC indicate a great potential of this strategy for building new monitoring platform in bioanalysis and clinical biomedicine. [ABSTRACT FROM AUTHOR]

An electrochemical sensor was fabricated for arsenite detection using graphene oxide-assisted generation of prussian blue nanoparticles as enhanced redox signal label. The 5′-thiolate-labeled (GT) 21 -ssDNA was first self-assembled on a gold electrode surface via Au-S bond. Graphene oxide can interact with ssDNA through π-π stacking interaction and facilitate the generation of prussian blue nanoparticles on its surface as an electrochemically active indicator. In the absence of arsenite, plenty of graphene oxide/prussian blue nanoparticles can be adsorbed on the electrode surface to produce a stronger redox signal of prussian blue nanoparticles. While in the presence of arsenite, (GT) 21 -ssDNA can recognize and combine with arsenite via hydrogen bonds to form (GT) 21 -ssDNA/arsenite complex with a frizzy structure. The conformational change of (GT) 21 -ssDNA led to less adsorption of graphene oxide/prussian blue nanoparticles on the electrode surface, resulting in a reduced redox response. The arsenite-induced (GT) 21 -ssDNA structure switching can be used for sensitive detection of arsenite with a linear range from 0.2 to 500 ppb and a detection limit down to 0.058 ppb. Benefiting from (GT) 21 -ssDNA containing arsenite recognition sequence, the proposed sensor exhibited excellent specificity against other heavy metal ions. The applicability of the electrochemical biosensor for arsenite assay in real water samples demonstrated the great potential of this strategy for trace arsenite detection in environment. [ABSTRACT FROM AUTHOR]

Previous researches of covalent organic frameworks (COFs) have shown their potential as fluorescent probes, but the regulation of their optical properties and recognition characteristics still remains a challenge, and most of reports required complicated post-decoration to improve the sensing performance. In this context, we propose a novel in-situ strategy to construct uracil-conjugated COFs and modulate their fluorescence properties for sensitive and selective mercury(II) detection. By using 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TAPPy) as fundamental blocks and 5-aminouraci (5-AU) as the functional monomer, a series of COFs (Py-COFs and Py-U-COFs-1 to Py-U-COFs-5) with tunable fluorescence were solvothermally synthesized through an in-situ Schiff base reaction. The π-conjugated framework serves as a signal reporter, the evenly and densely distributed uracil acts as a mercury(II) receptor, and the regular pores (channels) make the rapid and sensitive detection of the mercury(II) possible. In this research, we manage to regulate the crystalline structure, the fluorescence properties, and the sensing performance of COFs by simply changing the molar ratio of precursors. We expect this research to open up a new strategy for effective and controllable construction of functionalized COFs for environmental analysis. An in-situ strategy is proposed to construct uracil-conjugated COFs and modulate their fluorescence properties for sensitive and selective mercury(II) detection. The π-conjugated framework serves as a signal reporter, the evenly and densely distributed uracil acts as a mercury(II) receptor, and the regular pores (channels) make the rapid and sensitive detection of the mercury(II) possible. [Display omitted] • A novel in-situ strategy was proposed to construct uracil-conjugated COFs. • The crystalline structure and the fluorescence property of COFs can be facilely modulated. • The functionalized COFs demonstrate tunable recognition characteristics toward mercury(II). • Mercury(II) can be sensitively and selectively detected based on the fluorescence quenching. [ABSTRACT FROM AUTHOR]

Herein, a novel electrochemiluminescence resonance energy transfer (ECL-RET) biosensor using graphene quantum dots (GQDs) as donor and graphene oxide (GO) as acceptor for monitoring the activity of protein kinase was presented for the first time. Anti-phosphoserine antibody conjugated graphene oxide (Ab-GO) nonocomposite could be captured onto the phosphorylated peptide/GQDs modified electrode surface through antibody–antigen interaction in the presence of casein kinase II (CK2) and adenosine 5′-triphosphate (ATP), resulting in ECL from the GQDs quenching by closely contacting GO. This ECL quenching degree was positively correlated with CK2 activity. Therefore, on the basis of ECL-RET between GQDs and GO, the activity of protein kinase can be detected sensitively. This biosensor can also be used for quantitative analysis CK2 activity in serum samples and qualitative screening kinase inhibition, indicating the potential application of the developed method in biochemical fundamental research and clinical diagnosis. [ABSTRACT FROM AUTHOR]

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive detection of Cu 2+ is very important to prevent over-ingestion, and visual detection is preferred for practical applications. In this work, we developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters (hPEI-Cu NCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which were then conjugated to the surface of silica coated CdSe quantum dots (QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu 2+ ions, the fluorescence of Cu NCs can be drastically quenched, while the emission from QDs stayed constant to serve as a reference signal and the color of the probe changed from yellow-green to red, resulting in ratiometric and visualization detection of Cu 2+ ion with high accuracy. The detection limit for Cu 2+ was estimated to be 8.9 nM, much lower than the allowable level of Cu 2+ in drinking water (∼20 μM) set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu 2+ ion in complex real water samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] We reported a novel ECL biosensor for sensitive analysis of protein kinase activity. [•] GOx/Au NPs/DNA-biotin was used as the ECL signal amplification nanoprobe. [•] This strategy can in situ generate coreactant H2O2 to improve the luminol ECL signal. [•] Highly sensitive detection of PKA activity and inhibition is achieved. [ABSTRACT FROM AUTHOR]

Abstract: Small molecules or analytes present at low concentrations are difficult to detect directly using conventional surface plasmon resonance (SPR) techniques because only small changes in the refractive index of the medium are typically induced by the binding of these analytes. Here, we present an amplification technique using core–shell Fe3O4@Au magnetic nanoparticles (MNPs) for an SPR bioassay. To evaluate this amplification effect, a novel SPR sensor based on a sandwich immunoassay was developed to detect α-fetoprotein (AFP) by immobilizing a primary AFP antibody (Ab1) on the surface of a 3-mercapto-1-propanesulfonate/chitosan-ferrocene/Au NP (MPS/CS-Fc/Au NP) film employing Fe3O4@Au–AFP secondary antibody conjugates (Fe3O4@Au–Ab2) as the amplification reagent. The stepwise fabrication of the biosensor was characterized using UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. A calibration curve of Fe3O4@Au–Ab2 conjugates amplification for AFP detection was obtained to yield a correlation in the range of 1.0–200.0ngmL−1 with a detection limit of 0.65ngmL−1, and a significant increase in sensitivity was therefore afforded through the use of Fe3O4@Au–Ab2 conjugates as an amplifier. This magnetic separation and amplification strategy has great potential for the detection of other biomolecules of interest with low interference and high sensitivity by changing the antibody label used in the Fe3O4@Au–antibody conjugates. [Copyright &y& Elsevier]