Studies towards the exploitation of sonochemically formed microelectrode arrays for the development of electrochemical sensors

Microelectrodes offer a number of advantages for exploitation as electrochemical sensors such as imparting stir-independence to sensor responses and allowing lower limits of detection to be minimised. Microelectrode arrays offer an attractive route for increasing the current responses of microelectrodes, whilst still retaining their advantageous properties. Despite this, no commercial sensors, to date, have successfully employed microelectrode arrays, largely due to conventional fabrication routes proving too costly to be economically viable for the production of disposable sensing devices. Previous work carried out by this research group has described a novel and patented procedure for the fabrication of microelectrode arrays via the sonochemical ablation of insulating polymer films electrochemically deposited upon conductive surfaces. This format lends itself to mass fabrication due to the simplicity and inexpensiveness of the approach. This thesis describes work focussed towards the optimisation of each of the individual components involved in the formation of sonochemically fabricated microelectrode arrays. In particular, factors and techniques that may facilitate the commercial exploitation and mass fabrication of such arrays as generic sensing templates are described. Screen printed carbon has been investigated for its suitability as a host electrode. The comparative use of a number of possible activation methods to increase amperometric current responses at such electrodes is also described. Homogeneous poly(o-phenylenediamine) films of -40 nm thickness formed at the surfaces of screen printed carbon electrodes via the anodic electropolymerisation of o-phenylenediamine are shown to serve as effective diffusional barriers, thus insulating the underlying carbon electrodes. Microelectrode arrays formed by the sonochemical ablation of such films to expose microscopic areas of the underlying conductive substrates are seen to possess electrode element populations of -7.3 x 104 cm 2. Over 400 such sensors are shown to be able to be fabricated simultaneously with reproducibility of responses <4% relative standard deviation. Amperometric and cyclic voltammetric characterisations of the thus produced microelectrode arrays performed in model redox systems are shown to agree with accepted theoretical microelectrode behaviour, demonstrating sigmoidal shaped voltammograms, fluctuations in steady-state current responses of <10% with convection, scan rate independence and fast attainment (<20 seconds) of steady-state responses. Arrays of this type are also demonstrated to be suitable for exploitation within aqueous chlorine sensing devices, offering detection limits of <0.005 mg/l free chlorine, representing an order of magnitude lower than those obtainable via contemporary optical wet chemistry based approaches. In order to demonstrate further the applicability of this approach to the mass fabrication of disposable devices, methods for the deposition of a chemical modifying layer are also investigated, to avoid the need for additional reagents.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Studies towards the exploitation of sonochemically formed microelectrode arrays for the development of electrochemical sensors.

Microelectrodes offer a number of advantages for exploitation as electrochemical sensors such as imparting stir-independence to sensor responses and allowing lower limits of detection to be minimised. Microelectrode arrays offer an attractive route for increasing the current responses of microelectrodes, whilst still retaining their advantageous properties. Despite this, no commercial sensors, to date, have successfully employed microelectrode arrays, largely due to conventional fabrication routes proving too costly to be economically viable for the production of disposable sensing devices. Previous work carried out by this research group has described a novel and patented procedure for the fabrication of microelectrode arrays via the sonochemical ablation of insulating polymer films electrochemically deposited upon conductive surfaces. This format lends itself to mass fabrication due to the simplicity and inexpensiveness of the approach. This thesis describes work focussed towards the optimisation of each of the individual components involved in the formation of sonochemically fabricated microelectrode arrays. In particular, factors and techniques that may facilitate the commercial exploitation and mass fabrication of such arrays as generic sensing templates are described. Screen printed carbon has been investigated for its suitability as a host electrode. The comparative use of a number of possible activation methods to increase amperometric current responses at such electrodes is also described. Homogeneous poly(o-phenylenediamine) films of -40 nm thickness formed at the surfaces of screen printed carbon electrodes via the anodic electropolymerisation of o-phenylenediamine are shown to serve as effective diffusional barriers, thus insulating the underlying carbon electrodes. Microelectrode arrays formed by the sonochemical ablation of such films to expose microscopic areas of the underlying conductive substrates are seen to possess electrode element populations of -7.3 x 104 cm 2. Over 400 such sensors are shown to be able to be fabricated simultaneously with reproducibility of responses <4% relative standard deviation. Amperometric and cyclic voltammetric characterisations of the thus produced microelectrode arrays performed in model redox systems are shown to agree with accepted theoretical microelectrode behaviour, demonstrating sigmoidal shaped voltammograms, fluctuations in steady-state current responses of <10% with convection, scan rate independence and fast attainment (<20 seconds) of steady-state responses. Arrays of this type are also demonstrated to be suitable for exploitation within aqueous chlorine sensing devices, offering detection limits of <0.005 mg/l free chlorine, representing an order of magnitude lower than those obtainable via contemporary optical wet chemistry based approaches. In order to demonstrate further the applicability of this approach to the mass fabrication of disposable devices, methods for the deposition of a chemical modifying layer are also investigated, to avoid the need for additional reagents

New Techniques in Monitoring Water Pollution - Development of Sonochemically Fabricated Microarrays for the Determination of Pollutants.

The focus of this article is to describe a simple-to-use, disposable sensor suitable for the rapid determination of pollutants in aqueous media, utilising a novel sonochemical microelectrode fabrication technique. The use of screen- printing, electrochemical and sonochemical methods allows the production of microelectrode arrays capable of stir-independent determination of chlorine in water. These arrays permit the simultaneous measurement of free and total chlorine at concentrations between 0-20 ppm. Developments leading to production on a mass scale will be briefly discussed. A further system incorporating enzyme containing conductive polymers to give microelectrode arrays capable of detection of ultra-low levels of organophosphate pesticides will also be described. Acetylcholine esterase could be entrapped within conductive polyaniline protrusions and the effects of pesticides on its activity determined. Ultra low concentrations of pesticide were found to reduce the enzymes activity as measured electrochemically. These systems allow the detection of organophosphates at concentrations as low as (10-17 M)

Sonochemically fabricated microelectrode arrays for biosensors offering widespread applicability. Part I

A novel and patented procedure is described for the sonochemical fabrication of a new class of microelectrode array based sensor with electrode element populations of up to 2 x 105 cm-2. For some years it has been accepted that microelectrode arrays offer an attractive route for lowering minimum limits of detection and imparting stir (convectional mass transport) independence to sensor responses; despite this no commercial biosensors, to date, have employed microelectrode arrays, largely due to the cost of conventional fabrication routes that have not proved commercially viable for disposable devices. Biosensors formed by our sonochemical approach offer unrivalled sensitivity and impart stir independence to sensor responses. This format lends itself for mass fabrication due to the simplicity and inexpensiveness of the approach; in the first instance impedimetric and amperometric sensors are reported for glucose as model systems. Sensors already developed for ethanol, oxalate and a number of pesticide determinations will be reported in subsequent publications