Three-dimensional Pd@Pt core−shell nanostructures with controllable shape and composition were synthesized by using a one-step microwave heating method. The nanostructures with the morphology, structure, and composition being easily controlled through adjusting the molar ratio between Pt and Pd precursor were characterized by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), X-ray powder diffraction (XRD), and energy-dispersive X-ray (EDX) techniques. In addition, the electrocatalytic characteristics of these prepared Pd@Pt electrocatalysts with different Pd/Pt molar ratio for oxygen electro-reduction reaction (ORR) and methanol electro-oxidation reaction (MOR) were systematically investigated by voltammetry. The results show that Pd@Pt electrocatalysts exhibit higher catalytic activity than pure Pd and pure Pt catalysts for both the ORR and MOR, and the highest activity is obtained at the Pd@Pt electrocatalyst with a Pd/Pt molar ratio of 1:3. This result demonstrates that a higher performance of ORR and MOR could be realized at the novel core−shell electrocatalyst while Pt utilization also could be diminished. This method may open a general approach for the shape-controlled synthesis of bimetallic Pt−M nanocatalysts, which can be expected to have promising applications in fuel cells.

In this work, a highly sensitive electrochemiluminescence (ECL) assay was fabricated for the detection of human DNA (cytosine-5)-methyltransferase1 (DNMT1) activity in cancer cells. The ECL assay coupled hybridization chain reaction with a G-quadruplex/hemin DNAzyme biosensing strategy. The ECL intensity changes (ΔI) allowed detection of DNMT1 activity down to 0.09 U mL−1, and ΔI was proportional to the logarithm of the activity of DNMT1 within the range of 1.0 to 30.0 U mL−1 in buffer solution. It also showed high sensitivity to DNMT1 activity in A549 cells, with a detection limit of about 2 cells. This ECL assay provides a promising platform for profiling of the mutational cells of tumors and shows a great potential for application to DNA methylation-related clinical diagnostics.

Effective detection of DNA methyltransferase (DNMT) activity is significant for cancer research. Herein, we developed a sensitive electroanalytical method to detect human DNA (cytosine-5)–methyltransferase 1 (DNMT1) from crude lysates of cancer cells. In this assay, capture DNA having a preferred DNMT1 methylation site was immobilized on a gold electrode and then hybridized with gold nanoparticle (Au NP)–DNA complexes. The modified electrodes were equilibrated with the lysate and then incubated with methylation-sensitive restriction enzyme. If the lysate was negative for DNMT1 activity, the Au NP–DNA complexes would be cut by the restriction enzyme and released from the electrode. Conversely, restriction enzyme cleavage would be blocked by the fully methylated duplexes, and the Au NP–DNA complexes would remain on the electrode. Electroactive Ru(NH3)63+ was used as the signal reporter, because of its electrostatic attraction to DNA, resulting in an electrochemical signal. Since the electrochemical signal reflects the amount of Ru(III) redox and the amount of Ru(III) redox is correlated with the activity of DNMT1, the activity of DNMT1 is proportional to the electrochemical signal. The signal could be amplified by the numerous DNAs on the Au NPs and further amplified by Ru(III) redox recycling. With this method, a detection limit down to 0.3 U/mL for pure DNMT1 and 8 MCF-7 cells was achieved. DNMT1 activities of different cell lines were also successfully evaluated.

•Detect DNA demethylase activity by electrochemical DNA sensor strategy.•The principle relies on electrochemical signal changes of FcA redox label.•Combine the DNA demethylation and the BstUI endonuclease digestion.•A high sensitivity with low detection limit of 0.17 ng/mL of DNA demethylase.•The assay can be used for the related molecular diagnostics and drug screening.DNA demethylation and demethylase activity play important roles in DNA self-repair, and their detection is key to early diagnosis of fatal diseases. Herein, a facile electrochemical DNA (E-DNA) sensor was developed for the sensitive detection of DNA demethylation and demethylase activity based on an enzyme cleavage strategy. The thiol modified hemi-methylated hairpin probe DNA (pDNA) was self-assembled on a Au electrode surface through the formation of AuS bonds. The hemi-methylated pDNA served as the substrate of DNA demethylase (using methyl-CpG-binding domain protein 2 (MBD2) as an example). Following demethylation, the hairpin stem was then recognized and cleaved by BstUI endonuclease. The ferrocene carboxylic acid (FcA)-tagged pDNA strands were released into the buffer solution from the electrode surface, resulting in a significant decrease of electrochemical signal and providing a means to observe DNA demethylation. The activity of DNA demethylase was analyzed in the concentration ranging from 0.5 to 500 ng mL−1 with a limit of detection as low as 0.17 ng mL−1. With high specificity and sensitivity, rapid response, and low cost, this simple E-DNA sensor provides a unique platform for the sensitive detection of DNA demethylation, DNA demethylase activity, and related molecular diagnostics and drug screening.

We report a sensitive and selective approach for the DNA methyltransferase (MTase) activity assay and MTase inhibitor screening by coupling the fluorescence quenching of graphene oxide with site-specific cleavage of a restriction endonuclease.

We report a new strategy for detection of the methylation level and position in the Hsp53 tumor suppressor gene based on the electrochemiluminescence signal amplification combined with a conformation-switched hairpin DNA probe for improving selectivity.

Choline, as a marker of cholinergic activity in brain tissue, is very important in biological and clinical analysis, especially in the clinical detection of the neurodegenerative disorders disease. This work presents an electrochemical approach for the detection of choline based on prussian blue modified iron phosphate nanostructures (PB–FePO4). The obtained nanostructures showed a good catalysis toward the electroreduction of H2O2, and an amperometric choline biosensor was developed by immobilizing choline oxidase on the PB–FePO4 nanostructures. The biosensor exhibited a rapid response (ca. 2 s), low detection limit (0.4 ± 0.05 μM), wide linear range (2 μM to 3.2 mM), high sensitivity (∼75.2 μA mM−1 cm−2), as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid and 4-acetamidophenol did not cause obvious interference due to the low detection potential (−0.05 V versus saturated calomel electrode). This nanostructure could be used as a promise platform for the construction of other oxidase-based biosensors.

This work reports the development of a facile, one-step microwave heating method for the synthesis of graphene-supported Pd1Pt3 (Pd core/Pt shell) electrocatalysts. The structure and composition of the synthesized nanocomposites were characterized via transmission electron microscopy and atomic force microscopy as well as energy-dispersive X-ray, X-ray powder diffraction, FTIR, and Raman spectroscopies. Using voltammetry, the electrocatalytic characteristics of the graphene-supported Pd1Pt3 nanostructures were evaluated for the oxidation of methanol as a model reaction. The results show that the introduction of graphene increases the electrochemically active surface area of the Pd1Pt3 nanostructures. As compared to the unsupported Pd1Pt3 electrocatalyst, the graphene-supported Pd1Pt3 electrocatalyst exhibited 80% enhancement of the electrocatalytic specific mass current for the oxidation of methanol. This method may serve as a general, facile approach for the synthesis of graphene-supported bimetallic PtM electrocatalysts with increased utilization of the Pt metal, which is expected to have promising applications in fuel cells.

This work develops and validates an electrochemical approach for uric acid (UA) determinations in both endogenous (cell lysate) and physiological (serum) samples. This approach is based on the electrocatalytic reduction of enzymatically generated H2O2 at the biosensor of uricase−thionine−single-walled carbon nanotube/glassy carbon (UOx−Th−SWNTs/GC) with the use of Th−SWNTs nanostructure as a mediator and an enzyme immobilization matrix. The biosensor, which was fabricated by immobilizing UOx on the surface of Th−SWNTs, exhibited a rapid response (ca. 2 s), a low detection limit (0.5 ± 0.05 μM), a wide linear range (2 μM to 2 mM), high sensitivity (∼90 μA mM−1 cm−2), as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, 3,4-dihydroxyphenylacetic acid, 4-acetamidophenol, etc., did not cause any interference due to the use of a low operating potential (−400 mV vs saturated calomel electrode). Therefore, this work has demonstrated a simple and effective sensing platform for selective detection of UA in the physiological levels. In particular, the developed approach could be very important and useful to determine the relative role of endogenous and physiological UA in various conditions such as hypertension and cardiovascular disease.

This work develops a novel electrochemical approach for detection of the extracellular oxygen released from human erythrocytes. The sensing is based on the bioelectrocatalytic system of graphene integrated with laccase (Lac) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) toward the reduction of oxygen. ABTS and laccase are assembled on the surface of graphene, which is synthesized by a chemistry route, utilizing the π−π and electrostatic interactions of these components. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and FT-IR spectroscopy demonstrate that graphene has been successfully synthesized, and ABTS and laccase have been effectively assembled on a graphene surface with the formation of Lac−ABTS−graphene hybrid. The voltammetric results indicate that ABTS can be used as a redox mediator when it is in immobilized form. The hybrid deposited on the glassy carbon (GC) electrode is demonstrated to be a good bioelectrocatalyst for the reduction of oxygen with inherent enzyme activity, accepted stability, high half-wave potential (ca.670 mV vs NHE), and unimpeded electrical communication to the copper redox sites of laccase. Therefore, this study has not only established a novel approach of detection of extracellular oxygen but also provided a general route for fabricating a graphene-based biosensing platform via assembling enzymes/proteins on a graphene surface.

A gold nanoparticles (Au NPs)-graphene nanocomposite (Au–graphene nanocomposite) was prepared by electrochemically depositing Au NPs on the surface of graphene sheets, and characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and electrochemical methods. The morphology and size of the Au NPs could be easily controlled by adjusting the electrodeposition time and the concentration of precursor (AuCl4−). The electrocatalytic activities of the nanocomposites toward oxygen reduction and glucose oxidation were investigated by cyclic voltammetry. The results indicated that the nanocomposites had a higher catalytic activity than the Au NPs or graphene alone, indicating the synergistic effect of graphene and Au NPs. Therefore, this study has provided a general route for fabrication of graphene-based noble metal nanomaterials composite, which could be potential utility to fuel cells and bioelectroanalytical chemistry.

This work proposes a new electrochemical approach for specific detection of hepatitis C virus (HCV) based on the site-specific cleavage of BamHI endonuclease. The method was developed by immobilizing a synthetic probe DNA (a short thiol-capped single strand oligonucleotide) on the surface of a gold electrode via the –SH group at the 5′-terminus of the probe, and conjugating the electroactive label of ferroceneacetic acid (FcA) moiety to the 3′-terminus of the probe via formation of a covalent bond between the –NH2 and –COOH groups. The FcA-labeled probe was then hybridized with target cDNA (an oligonucleotide related to HCV) and cleaved by BamHI endonuclease (a site-specific endonuclease recognizing the duplex symmetrical sequence 5′–GGATCC–3′ and catalyzing double-stranded cleavage between the guanines). After digestion by BamHI, the DNA hybrid was cleaved at a specific site, and the FcA label was removed from the gold electrode surface leading to a decrease or disappearance of the electrochemical signal of the label. The extent of decrease was related to the concentration of target cDNA in solution, which forms the basis of quantitative detection of target cDNA. The detection is based on the variation of voltammetric signal (Δi) of FcA label before and after digestion with BamHI. It was demonstrated that the value of Δi has a linear relationship with the concentration of the HCV DNA (cDNA) ranging from 0.05 to 4.0 μM with a detection limit of (0.5 ± 0.2) nM at a signal/noise of 3. Moreover, the developed method has a high selectivity with ability to discriminate the complementary target DNA sequence from single-base mismatched DNA sequence, and can also be used for detection of HCV in real clinical samples. The major advantages of this enzymatic cleavage assay are its good specificity, ease of performance, and the ability to perform real-time monitoring. The proposed protocol can be taken as a general method of DNA detection and is expected to be applicable to other types of DNA analysis.

A new electrocatalyst, palladium nanoparticle−single-walled carbon nanotube (Pd−SWNTs) hybrid nanostructure, for the nonenzymatic oxidation of glucose was developed and characterized by X-ray diffraction (XRD) and the transmission electron microscope (TEM). The hybrid nanostructures were prepared by depositing palladium nanoparticles with average diameters of 4−5 nm on the surface of single-walled carbon nanotubes (SWNTs) via chemical reduction of the precursor (Pd2+). The electrocatalyst showed good electrocatalytic activity toward the oxidation of glucose in the neutral phosphate buffer solution (PBS, pH 7.4) even in the presence of a high concentration of chloride ions. A nonenzymatic amperometric glucose sensor was developed with the use of the Pd−SWNT nanostructure as an electrocatalyst. The sensor had good electrocatalytic activity toward oxidation of glucose and exhibited a rapid response (ca.3 s), a low detection limit (0.2 ± 0.05 μM), a wide and useful linear range (0.5−17 mM), and high sensitivity (∼160 μA mM−1 cm−2) as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid, 4-acetamidophenol, 3,4-dihydroxyphenylacetic acid, and so forth did not cause any interference due to the use of a low detection potential (−0.35 V vs SCE). The sensor can also be used for quantification of the concentration of glucose in real clinical samples. Therefore, this work has demonstrated a simple and effective sensing platform for nonenzymatic detection of glucose.

The effects of ionic liquids (ILs) on the catalytic activity of enzymes were studied by approaches of electrochemistry and quantum chemistry calculation in this work. Three types of ILs, namely, [bmpyri]BF4, [bmpyrro]BF4, and [bmim]BF4, were selected to address the effects of different types of ILs on the electrocatalytic activity of glucose oxidase (GOx) toward the oxidation of glucose. ILs and GOx were assembled on the surface of an electrode via single-walled carbon nanotubes (SWNTs) and poly(sodium 4-styrenesulfonate) (PSS) utilizing the electrostatic interaction. Spectroscopic results indicated that ILs did not affect the conformation of the enzyme. The cyclic voltammetric results showed that the electrocatalytic activity of the GOx−IL−PSS−SWNTs/GC electrode was lower than that of the GOx−SWNTs/GC electrode. The characteristic kinetic constants of the enzymatic reaction were evaluated from the cyclic voltammograms under a substrate-saturated condition. The values of the characteristic rate constant obtained at each IL-containing enzyme electrode were lower than those obtained at the GOx−SWNTs/GC electrode and decreased following the sequence of SWNTs > [bmpyri] > [bmpyrro] > [bmim]. The theoretical calculations combined with experiments were employed to address the interaction between the ILs and SWNTs, showing that the presence of IL on the surface of SWNTs could significantly affect the electrical transfer properties of the nanotube and led to the decrease of the electrocatalytic activity of the GOx−IL−PSS−SWNTs/GC electrode. These results indicate that the nature of ILs is the main factor, which affects the electrocatalytic activity of the GOx−IL−PSS−SWNTs/GC electrodes toward the oxidation of glucose. The results of this study are directly relevant for those applications where ILs are employed in the form of thin films supported on solid surfaces, such as the designing of the related biosensor, microelectronic devices in the ILs-containing system, and so forth.

We report a sensitive and selective approach for the DNA methyltransferase (MTase) activity assay and MTase inhibitor screening by coupling the fluorescence quenching of graphene oxide with site-specific cleavage of a restriction endonuclease.

We report a new strategy for detection of the methylation level and position in the Hsp53 tumor suppressor gene based on the electrochemiluminescence signal amplification combined with a conformation-switched hairpin DNA probe for improving selectivity.