Evidence of monolayer formation via diazonium grafting with a radical scavenger: electrochemical, AFM and XPS monitoring.

This paper analyzes the impact of the use of a radical scavenger on organic films generated by aryldiazonium electrografting in terms of thickness, morphology and chemical composition. Glassy carbon (GC) and pyrolyzed photoresist films (PPFs) were modified by electrochemical reduction of 4-nitrobenzenediazonium salt in the presence of various amounts of 2,2-diphenyl-1-picrylhydrazyl (DPPH). The thicknesses of the organic films have been measured by atomic force microscopy (AFM) and the lower threshold values confirm that it is possible to reach a monolayer by radical trapping. X-ray photoelectron spectroscopy (XPS) highlights a decrease in the proportion of nitrophenyl groups grafted via azo bridges as the DPPH concentration decreases and the film thickness increases. A correlation of electrochemical, XPS and AFM data confirms that not all nitrophenyl groups are electroactive in films greater than 2 nm thick.

Evidence for covalent bonding of aryl groups to MnO2 nanorods from diazonium-based grafting.

We show here that the surface of MnO2 nanorods can be modified with aryl groups by grafting from aqueous and non-aqueous solutions of aryldiazonium salts. X-ray photoelectron spectroscopy provides direct evidence for covalent bonding of aryl groups to MnO2 through surface oxygens.

Detection of two distinct substrate-dependent catabolic responses in yeast cells using a mediated electrochemical method.

Mediated electrochemical detection of catabolism in prokaryotic cells is well documented; however, the application of this technique to eukaryotic cells has received less attention. Two catabolic substrate-dependent mediated electrochemical signals were detected in the yeast Saccharomyces cerevisiae. The signal using a single hydrophilic mediator (ferricyanide) is small whereas the response using a double mediator system comprising a hydrophilic and a lipophilic mediator (ferricyanide and menadione) is up to three orders of magnitude larger. The behaviour of each response during cell ageing is different: the single mediator response increases whereas the double mediator response decreases. This difference indicates that the two signals originate at different points in the catabolic pathways. In S. cerevisiae the double mediator response is proposed to originate from the reduction of the lipophilic mediator by NADPH produced in the pentose phosphate pathway. The single mediator signal arises from reduction of the hydrophilic mediator by an extracellular redox species produced in response to the presence of glucose.

Characterisation of a thermophilic L-glutamate dehydrogenase biosensor for amperometric determination of L-glutamate by flow injection analysis.

Carbon paste wax electrodes incorporating thermophilic L-glutamate dehydrogenase, NADP and a polymeric toluidine blue O (poly-TBO) mediator have been characterised for the amperometric determination of L-glutamate at 313-318 K in a flow injection analysis (FIA) system. The biosensors exhibit good sensitivity, mechanical stability and reproducibilty, unlike carbon paste- or carbon wax-based electrodes under the same conditions. The carbon paste wax electrode responds linearly to L-glutamate up to 40 mM, the detection limit is 0.3 mM and the RSD (n = 10) for 5 mM L-glutamate was 7.6%. The response to some potential interferents has been quantified. Addition of finely ground hexaammineruthenium (III) trichloride ([Ru(NH3)6]Cl3) to the carbon paste wax electrodes decreases the FIA peak width and increases the peak current. The metal complex appears to accelerate the rate of oxidation of NAD(P)H by poly-TBO.