Yansha Gao

Overoxidized polypyrrole/graphene nanocomposite with good electrochemical performance as novel electrode material for the detection of adenine and guanine.

Most conducting polymer/graphene composites have excellent electrical conductivity. However, the background currents of these composites modified electrodes are much larger. In order to improve the sensitivities of these methods, it is necessary to decrease the background signal. In this paper, porous structure films of overoxidized polypyrrole/graphene (PPyox/GR) have been electrochemically coated onto glassy carbon electrode (GCE) and successfully utilized as an efficient electrode material for the quantitive detection of adenine and guanine, two of the most important components of DNA and RNA. The permselective polymer coatings with low background current could improve the selectivity and sensitivity of microelectrodes for the electropositive purine bases. The GRs into these polymers would further improve sensitivity by increasing the electroactive surface area. The electrochemical sensor can be applied to the quantification of adenine and guanine with a linear range covering 0.06-100 µM and 0.04-100 µM, and a low detection limit of 0.02 μM and 0.01 μM, respectively. More importantly, the proposed method was applied to quantify adenine and guanine in calf thymus DNA with satisfactory results.

A label-free electrochemical immunosensor for carcinoembryonic antigen detection on a graphene platform doped with poly(3,4-ethylenedioxythiophene)/Au nanoparticles

In this work, a two-step method was developed for the fabrication of a graphene sensing platform doped with poly(3,4-ethylenedioxythiophene)/Au nanoparticles (AuNPs/PEDOT/GR). PEDOT nanorods grown on graphene oxide nanosheets (PEDOT/GO) were firstly synthesized by liquid–liquid interfacial polymerization, followed by the chemical reduction of HAuCl4 by NaBH4. During the reduction process, GO doped in the PEDOT was also reduced to a more conductive form of GR. The obtained AuNPs/PEDOT/GR showed excellent conductivity and large surface area. Thus, a simple and sensitive label-free immunosensor based on AuNPs/PEDOT/GR nanocomposite has been proposed to detect carcinoembryonic antigen (CEA) by measuring the change of electrochemical response before and after the immunoreaction. Under the optimized conditions, the linear range of the proposed immunosensor is estimated to be from 0.0004 to 40 ng mL−1 (R2 = 0.9969) and the detection limit is estimated to be 0.1 pg mL−1 at a signal-to-noise ratio of 3. Moreover, the immunosensor was examined for use in the determination of CEA in real human serum samples with satisfactory results.

Facile one-pot preparation of Pd–Au/PEDOT/graphene nanocomposites and their high electrochemical sensing performance for caffeic acid detection

In this study, bimetallic Pd–Au/PEDOT/graphene (Pd–Au/PEDOT/rGO) nanocomposites were facilely prepared in an aqueous medium by a one-pot method. In addition to the Pd–Au/PEDOT nanoparticles, dendritic bimetallic Pd–Au nanoclusters were also obtained in the composites, which were verified by transmission electron microscopy and element analysis mapping characterization. The morphology of the nanocomposites was greatly influenced by the molar ratio of the added metal salt precursors. X-ray photoelectron spectroscopy and X-ray diffraction analyses indicated the presence of synergism and electron exchange between the Pd–Au bimetallic nanostructures, which play an important role in the enhancement of the electrocatalytic activity of the composite toward the oxidation of caffeic acid (CA). Under optimized conditions, the Pd–Au/PEDOT/rGO modified glassy carbon electrode showed a wide linear range of 0.001–55 μM and a low detection limit of 0.37 nM (S/N = 3) for CA detection. These results provide valuable insight on the development of novel modified electrodes based on bimetallic graphene nanocomposites for high performance electrochemical sensors.

Nickel clusters grown on three-dimensional graphene oxide–multi-wall carbon nanotubes as an electrochemical sensing platform for luteolin at the picomolar level

This study focuses on enhancing the catalytic activity of metallic Ni by using various nanostructured carbon materials, including 1D multi-wall carbon nanotubes (MWCNTs), 2D graphene oxide (GO) and graphene (GR), and 3D graphene oxide–multi-wall carbon nanotubes (GO–MWCNTs) as supporting matrices for the fabrication of an electrochemical sensor for detecting the flavonoid luteolin. Ni clusters were prepared by a facile electrochemical approach and the metallic Ni on various carbon supports exhibited different morphologies, which were characterized by scanning electron microscopy (SEM) and Raman spectra. The electrocatalytic performance of Ni-based materials towards luteolin oxidation was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that Ni clusters supported on GO–MWCNTs (Ni/GO–MWCNTs) were profoundly superior to other carbon materials, with a greatly enhanced current. This is attributed not only to the excellent electric conductivity and large surface-to-volume ratio of Ni/GO–MWCNTs, but also to the unique 3D carbon nanostructure that facilitates the easy access of the electrolyte and analyte to the modified electrode surface and promotes the reaction kinetics. Under the optimal conditions, the anodic peak current was linear to the concentration of luteolin in the range from 1 pM to 15 μM with a detection limit of 0.34 pM (S/N = 3). The good analytical performance, low cost and straightforward preparation method made this novel electrode material promising for the development of an effective luteolin sensor.

A universal strategy for the facile synthesis of a sandwich-structured Pt–graphene–Pt nanocomposite for salbutamol sensing

In this work, a sandwich-structured Pt–graphene–Pt (P–Gr–P) nanocomposite has been prepared by a two-step method including (i) a chemical and (ii) an electrochemical reduction process. The P–graphene oxide–P (P–GO–P) nanocomposite was firstly synthesized by an in situ growth method, during which platinum nanoparticles (PtNPs) grew on both sides of GO. In the second step, P–GO–P was coated onto a glass carbon electrode (GCE). In this process, GO in the P–GO–P nanocomposite was reduced to a more conductive form of graphene (Gr). The obtained sandwich-structured P–Gr–P can effectively separate the individual layers of Gr sheets from each other, prevent the agglomeration of Gr sheets and improve the conductivity of the Gr film. In addition, the electrocatalytic properties of the as-prepared P–Gr–P nanocomposite towards the oxidation of salbutamol (SAL) were investigated. Results revealed that the sandwich-structured P–Gr–P nanocomposite with higher electrochemically active surface area showed better electrocatalytic activity toward SAL oxidation than PtNPs–Gr prepared by using the one-step electrochemical co-deposition method. On the basis of the excellent electrochemical activity of the P–Gr–P nanocomposite, a highly sensitive electrochemical platform was developed for the rapid detection of SAL. The present work provides an interesting strategy to prepare a Gr-based nanocomposite for electrochemical sensors.

Facile fabrication of three-dimensional graphene microspheres using β-cyclodextrin aggregates as substrates and their application for midecamycin sensing

Three-dimensional (3D) graphene (GR) microspheres have been successfully prepared for the first time using a simple, easy and green method using β-cyclodextrin aggregates (β-CDAs) as substrates, which could be easily obtained from concentrated aqueous solutions of β-CD. The 3D GR/β-CDAs composites synthesized were characterized using scanning electron microscopy, transmission electron microscopy, ultraviolet/visible spectroscopy, and Raman spectroscopy. A possible formation mechanism was derived. The as-prepared 3D GR/β-CDAs microspheres provided multidimensional electron transport pathways, and this has been exploited in an electrode material for the electrocatalytic oxidation of midecamycin (MD), a widely used macrolide antibiotic. Electrochemical results indicated that the as-prepared 3D GR/β-CDAs microspheres exhibited a higher electrocatalytic activity towards MD oxidation than two-dimensional (2D) GR or β-CDAs, which could be mainly attributed to the improved electrical properties and large surface area of the composite and the high recognition and enrichment capability of β-CDAs. Under optimal conditions, the peak currents on a 3D GR/β-CDA microsphere modified electrode increased linearly with the concentration of MD in the range 0.07–250 μM. The detection limit of MD reached 20 nM (S/N = 3). The present method is promising for the synthesis of high-performance catalysts for sensors, fuel cells and gas-phase catalysis.