Gareth P. Keeley

Electrochemical ascorbic acid sensor based on DMF-exfoliated graphene

This paper describes the electron transfer properties of graphene nano-sheets (GNSs) immobilised on pyrolysed photoresist film (PPF) electrodes. The former are produced by the dispersion and exfoliation of graphite in dimethylformamide, and they are characterised using transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. Cyclic voltammetry and electrochemical impedance spectroscopy are used to quantify the effect of the GNSs on electrochemical surface area and on electron transfer kinetics. Compelling evidence is reported in relation to the importance of edge-plane sites and defects in the promotion of electron transfer at carbon nanostructures. A novel ascorbic acid (vitamin C) sensor is presented based on the PPF/GNS system, which is effective in the range 0.4 to 6.0 mM, with a 0.12 mM detection limit. The selectivity of the sensor is demonstrated using a commercially available vitamin C supplement. This is the first report of the electrochemical properties of graphene nano-sheets produced using liquid-phase exfoliation, and it will serve as an important benchmark in the development of inexpensive graphene-based electrodes with high surface area and electro-catalytic activity.

Simultaneous electrochemical determination of dopamine and paracetamol based on thin pyrolytic carbon films

This paper describes the determination of dopamine and paracetamol using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The selective, stable and reproducible simultaneous measurement of the two compounds is achieved using thin pyrolytic carbon (PyC) films as working electrodes. These are created via a reliable, non-catalytic chemical vapour deposition (CVD) process, and the electron transfer characteristics of the films are optimised using a simple oxygen plasma treatment. This new class of carbon electrode can detect dopamine in the range 18 to 270 μM, with a 2.3 μM limit of detection (LoD), while simultaneously sensing paracetamol in the range 15 to 225 μM (LoD 1.4 μM). A 225 mV separation between the two competing signals is realised. The accuracy of the sensor is demonstrated using human serum and commercially available pharmaceutical products. This is the first report of the application of PyC to this problem, and the performance is shown to be competitive with the leading carbon electrodes available today, particularly edge-plane pyrolytic graphite (EPPG). This work will serve as an important benchmark in the development of inexpensive, disposable, high-performance nano-structured electrodes for sensors, fuel cells and energy conversion.

Gas phase controlled deposition of high quality large-area graphene films

A gas phase controlled graphene synthesis resembling a CVD process that does not critically depend on cooling rates is reported. The controllable catalytic CVD permits high quality large-area graphene formation with deft control over the thickness from monolayers to thick graphitic structures at temperatures as low as 750 degrees C.

Immobilized enzyme-single-wall carbon nanotube composites for amperometric glucose detection at a very low applied potential

The behaviour of support electrodes modified with randomly dispersed single-wall carbon nanotube meshes containing adsorbed glucose oxidase with respect to amperometric glucose detection at a low potential is demonstrated.

Low temperature graphene growth

We demonstrate the growth of graphene films on nickel substrates by chemical vapour deposition using acetylene at temperatures as low as 750 degrees celsius, opening a viable route for its scalable production. Raman spectroscopy was used to confirm defect-free mono and multilayer graphene at and above this temperature, and of defective graphene at lower temperatures. Atomic force microscopy and scanning electron microscopy performed directly on the films give an indication of graphene flake size, morphology and also the topography on substrate. An unexpected dependence of graphene thickness on precursor dwell time is reported. This together with low temperature growth suggests deficiencies in existing growth models and hints at a more complicated growth mechanism.

Prussian blue-functionalised graphene in the amperometric detection of peroxide and hydrazine

The electrochemical detection of hydrogen peroxide, H2O2, and hydrazine, N2H4, is of considerable interest because of the serious health risks associated with these compounds. The unique zeolite structure of Prussian blue, Fe4[Fe(CN)6]3, endows it with excellent catalytic activity towards these small molecules, but its immobilisation on suitable support materials is limited by its solubility at neutral and basic pH values. Here we report an electroanalytical sensor for peroxide and hydrazine based on composites of Prussian blue and graphene nano-sheets (GNSs). The latter are fabricated using the liquid-phase exfoliation of graphite. When immobilised on graphene, Prussian blue is shown to exhibit higher sensitivity towards these analytes than a number of commercially available graphitic supports, including edge-plane pyrolytic graphite (EPPG) electrodes. The incorporation of graphene into electode systems could lead to great advances in sensor technology for these and many other species of interest.