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A facile and sensitive method for the quantitative detection of telomerase and in situ imaging of intracellular telomerase is developed by using a graphene oxide (GO)-based fluorescent nanosensor. The nanosensor consists of a fluorescent DNA (P1) adsorbed on the GO surface. Here, GO serves not only as a fluorescence quencher but also as a carrier to successfully transport P1 into cancer cells as a signal reporter. P1 is a dye-labeled single-stranded DNA complementary to the telomeric repeated sequence, and initially the combination of P1 and GO exhibits minimal background fluorescence. When telomerase extends its repeat units of TTAGGG on the 3′-end of the primer-DNA, the fluorescence of P1 is subsequently recovered because the telomeric repeated sequence can hybridize with P1 and liberate it from the GO surface. This method enables the determination of telomerase activity down to 10 cells. For the in situ detection of telomerase, upon endocytosis of the P1/GO combinatorial probe into living cancer cells, the intracellular telomerase extends its primer to produce the telomeric repeated sequence and then turns on the fluorescence of P1, which can be directly monitored by confocal laser scanning microscopy. The feasibility of the assay is further investigated by treating with telomerase-related drugs, and the results demonstrate its potential in antitumor drug screening and cancer therapy evaluation. [ABSTRACT FROM AUTHOR]

Abstract: A homogeneous chitosan–ferrocene/graphene oxide/glucose oxidase (CS–Fc/GO/GOx) nanocomposite film was successfully constructed as a novel platform for the fabrication of glucose biosensor. The morphologies and electrochemistry of the nanocomposite film were investigated by using scanning electron microscopy and electrochemical techniques including electrochemical impedance spectroscopy and cyclic voltammetry, respectively. Results demonstrated that the uniformly dispersed GO within the CS matrix could significantly improve the stability of GO and make it exhibit a positive charge, which was more favorable for the further immobilization of biomolecules, such as GOx, with higher loading. Further attaching redox mediator ferrocene group (Fc) to CS could not only effectively prevent the leakage of Fc from the matrix and retain its electrochemical activity, but also improve the electrical conductivity of CS and promote the electron-transfer between GOx and electrode. Biosensors based on this CS–Fc/GO/GOx film had advantages of fast response, excellent reproducibility, high stability, and showed a linear response to glucose in the concentration range from 0.02 to 6.78mM with a detection limit of 7.6μM at a signal-to-noise ratio of 3 and exhibited a higher sensitivity of 10μAmM−1 cm−2. The proposed strategy based on CS–Fc/GO nanocomposite for the immobilization of enzymes can be of practical relevance for the facile design of biosensors, as well as for the construction of new multifunctional bioelectrochemical systems. [Copyright &y& Elsevier]

[Display omitted] • Phosphate functionalized COF/rGO was synthesized using post-synthetic modification. • Tb-BD-P/rGO exhibited excellent physicochemical stability and rapid uranyl mass transfer ability. • TB-BD-P/rGO enabled photoelectrothermal synergistic photocatalytic reduction of uranium. • Tb-BD-P/rGO performed excellent removal rates (>95 %) in actual strong acid nuclear wastewater. Photocatalytic reduction is becoming an effective method to remove UVI from uranium mine wastewater. Herein, 1,3,5-benzotrialdehyde (Tb) and 4,4′-diaminobiphenyl (BD) used as monomers of covalent organic framework (COF) are in situ growth on graphene oxide (GO) surfaces to obtain Tb-BD/rGO. Then, Tb-BD/rGO is converted into Tb-BD-P/rGO by asymmetric hydrogen phosphorylation, which is served as a new material for photocatalytic reduction of uranium via photoelectrothermal synergy. Benefiting from the transformation of dynamic imine bonds into irreversible carbon–nitrogen single bonds, Tb-BD-P/rGO expresses remarkable chemical and thermal stability. The introduction of phosphate groups improve the electronegativity and hydrophilicity of Tb-BD-P/rGO, which contribute to rapid transportation of uranium. In addition, the introduction of rGO achieves excellent photothermal conversion, accelerating the adsorption kinetics of uranium. Meanwhile, the π-π interaction between Tb-BD-P and rGO promotes inter-interfacial electron transfer and reduces the complexation of electron-hole pairs during the photocatalytic process, further improving photocatalytic performance. Therefore, Tb-BD-P/rGO demonstrates exceptional removal uranium rates (>95 %) in uranium mine wastewater by synergistically photoelectrothermal integration, offering a pathway for developing multifunctional and integrated photocatalysts. [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]

Heavy metal ion pollution has threatened environmental and human safety. Therefore, there is a remarkable demand to detect heavy metal ions in a fast, sensitive, and selective way. Although conventional sensors have been designed and widely applied in heavy metal ion determination, they present many limitations and challenges. Graphene-based nanotechnology overcomes these challenges and endows the sensing platform a better performance. In this overview, studies concerning graphene-based optical nanosensors for heavy metal ion detection have been summarized, paying special attention to sensors based on graphene, graphene oxide, and graphene quantum dots. In addition, the prospects and developing trends of nanosensors for heavy metal ion analysis are also proposed. [ABSTRACT FROM AUTHOR]

We propose an electrochemical assay for As(III) based on trithiocyanuric acid deposited reduced graphene oxide (TTCA/rGO) using square wave anodic stripping voltammetry (SWASV). In this work, TTCA/rGO is prepared by a simple one-pot method using NaBH 4 as the reducing agent. Many TTCA molecules are successfully deposited on the surface of rGO through π-π conjugation, which endows the TTCA/rGO with excellent adsorption ability of As(III) via As−S bond. Combining the outstanding conductivity of rGO, the response of electrochemical current for As(III) determination is greatly amplified in the electrochemical detection process. Under optimum conditions, the TTCA/rGO modified gold electrode shows high sensitivity and good selectivity for the detection of As(III) with a low detection limit down to 0.054 ppb, which is promising to be applied for the rapid and sensitive determination of As(III) in complicated samples. [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]

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]

Highlights: [•] PDA/GO platform for the facile preparation of protein stationary phase was developed. [•] PDA/GO is endowed with the adhesive nature and high adsorption capacity. [•] Integrating BSA onto PDA/GO platform-based PDMS microchip greatly increased the phase ratio. [•] This protocol simplified the immobilization methodology of proteins in OT-CEC microdevice. [ABSTRACT FROM AUTHOR]

Abstract: Carbohydrate–protein interactions mediate the important physiological and pathophysiological processes in living organism. Their study has attracted great attention due to its importance in understanding these biological processes and in fabricating biosensors for diagnostics and drug development. Here, by using concanavalin A (ConA) as a model protein, a novel surface plasmon resonance (SPR) sensor was developed for sensitive detection ConA. In this sensing platform, dextran (Dex) capped gold nanoparticles (Dex-Au NPs) were initially synthesized in one-pot and utilized as amplification reagent. After deposition of graphene oxide (GO) on the SPR gold film, phenoxy-derivatized dextran (DexP) was assembled onto the GO-modified gold chip surface through π–π interaction. The resultant GO/DexP sensing interface could specifically capture ConA which could further react with Dex-Au NPs through the specific interaction between ConA and Dex, forming a sandwich configuration. The morphologies and the electrochemistry of the formed sensing surface were investigated by using scanning electron microscopy and electrochemical techniques including electrochemical impedance spectroscopy and cyclic voltammogram. Owing to the high surface area of GO and the excellent amplification of Dex-Au NPs, the developed sandwich SPR sensor successfully fulfilled the sensitive detection of ConA in the range of 1.0–20.0μgmL−1 with a detection limit of 0.39μgmL−1. Compared to the direct assay format, the prepared sandwich SPR sensor led to an improvement of 28.7-fold in the sensitivity. The results demonstrated that the proposed method might provide a new direction in designing high-performance SPR biosensors for sensitive and selective detection of a wide spectrum of biomolecules. [Copyright &y& Elsevier]

Highlights: [•] A strategy for construction of GO/Fe3O4 MNCs-based on-chip enzymatic microreactor was proposed. [•] The magnetism of Fe3O4 NPs can make enzymatic microreactor conveniently manipulated and replaceable. [•] Such an enzymatic microreactor was successfully applied to the sensitive detection of pesticide. [Copyright &y& Elsevier]

Abstract: A novel “smart” electrochemical affinity nanobiosensor with “on-off” switchable property was designed for the ultrasensitive determination of glucose. The sensing approach was based on the glucose-ConA-dextran competitive system induced charge evolution in the use of graphene oxide (GO) as transducer element, resulting in the enhancement of interfacial electron transfer kinetics between the redox probe and the electrode. As concanavalin A (ConA) constituent was pH-sensitive, when the ConA-DexP/GO film electrode switched in probe Fe(CN)6 3−/4− solution between pH 4.0 and 8.0, the film was cycled between the “on” and “off” states by the electrostatic attraction and repulsion of Fe(CN)6 3−/4− to and from the electrode surface. Upon introduction of glucose into the ConA-DexP/GO complex at the “off” state, glucose competed with DexP for ConA and displaced ConA from the GO platform, resulting in gradual decrease of the surface negative charge as well as the resistance of probe for electron communication on the sensor surface, and making the switching from “off” state to “on” state simultaneously. This ultrasensitive glucose nanobiosensor had a broad linearity between the decrease in electron transfer resistance (ΔR) and the glucose concentration over a range from 5.0μM to 9.0mM with a detection limit as low as 0.34μM. The proposed method showed potential application for fabricating novel biosensors and bioelectronic devices. [Copyright &y& Elsevier]