Barry G. D. Haggett

Redox mediated biosensors incorporating cultured fish cells for toxicity assessment

Fish are an important genus within ecosystems, and practical sensing devices, incorporating fish cells, could be used with advantage for environmental monitoring and protection. In this paper, redox mediated biosensors were prepared by immobilizing cultured fish cells at a carbon electrode surface. EPC (from carp) and BF-2 (from bluegill sunfish) cells could be monitored by using a lipophilic mediator (e.g. 2,6-dimethylbenzoquinone) added to the solution bathing the sensor. Currents measured in the external circuit were indicative of the metabolic activity of the immobilized cells and the sensors could be used to determine the presence of chemicals within the bathing medium that perturbed their normal metabolic status.

Electrochemical determination of silver in photographic solutions using fixed-volume single-use sensors

Electrochemical methods are described for the determination of silver ions in photographic processing solutions using a generic sensor design. The sensor consists of three electrodes (working, auxiliary and pseudo-reference) screen-printed with carbon ink. Silver can be measured between 100 µg l–1 and 5 g l–1 encompassing the concentrations of silver in the various stages of photoprocessing from fixer to effluent. Square-wave voltammetry and chronoamperometry were used for low and high silver concentrations, respectively.

Electrochemical detection of aluminium using single-use sensors

An electrochemical method for the direct detection of aluminium using single-use sensors is described. The sensor consists of three electrodes (working, auxilliary and pseudo-reference) screen-printed with carbon ink. Aluminium is accumulated at the carbon electrode at –1.6 V (vs. pseudo-reference) in zinc sulfate electrolyte for 90 s prior to anodic stripping using differential-pulse voltammetry. Linear calibrations were obtained between 10 and 450 ppb using the aluminium oxidation peak. The limit of detection was 8 ppb Al3+.

Silver nanoparticles and magnetic beads with electrochemical measurement as a platform for immunosensing devices.

The simplicity and analytical utility of silver nanoparticles used as immunolabels with screen-printed measurement electrodes is illustrated by demonstrating an appropriate analytical signal for myoglobin (a protein marker for muscle damage) across a range of concentrations of physiological interest for distinguishing potential myocardial infarctions from normal background levels in serum. Silver nanoparticles were used as labels on one of a pair of anti-myoglobin clones while the other clone was covalently attached to magnetic beads. The two clones were selected so as to bind to different sites on the target protein and allow the formation of complexes containing both magnetic beads and silver nanoparticles. The magnetic beads enabled protein captured from test samples to be separated from other components, while the silver nanoparticles enabled the protein to be quantified. An oxidising potential, applied to screen-printed carbon electrodes, was used to dissolve silver without the need for an external oxidising agent. Silver ions released in the process were subsequently accumulated at the measurement electrodes by applying a suitable reducing potential and, finally, analytical signals were obtained by integrating the charges passed when accumulated silver was stripped from the electrodes by applying a potential ramp. The magnitudes of the measured charges were indicative of the concentrations of myoglobin in each of the test solutions.

Hexacyanoferrate(III) as a mediator in the determination of total iron in potable waters as iron(II)-1,10-phenanthroline at a single-use screen-printed carbon sensor device.

Hexacyanoferrate(III) was used as a mediator in the determination of total iron, as iron(II)-1,10-phenanthroline, at a screen-printed carbon sensor device. Pre-reduction of iron(III) at -0.2V versus Ag/AgCl (1M KCl) in the presence of hexacyanoferrate(II) and 1,10-phenanthroline (pH 3.5-4.5), to iron(II)-1,10-phenanthroline, was complete at the unmodified carbon electrode surface. Total iron was then determined voltammetrically by oxidation of the iron(II)-1,10-phenanthroline at +0.82V, with a detection limit of 10microg l(-1). In potable waters, iron is present in hydrolysed form, and it was found necessary to change the pH to 2.5-2.7 in order to reduce the iron(III) within 30s. A voltammetric response was not found at lower pH values owing to the non-formation of the iron(II)-1,10-phenanthroline complex below pH 2.5. Attempts to incorporate all the relevant reagents (1,10-phenanthroline, potassium hexacyanoferrate(III), potassium hydrogen sulphate, sodium acetate, and potassium chloride) into a modifying coated PVA film were partially successful. The coated electrode behaved very satisfactorily with freshly-prepared iron(II) and iron(III) solutions but with hydrolysed iron, the iron(III) signal was only 85% that of iron(II).

Enhancement by Copper(II) of the voltammetric signal of vitamin B2 applied to its determination in breakfast cereals.

Addition of copper(II) to breakfast cereal samples was shown to significantly enhance the analytical signal obtained by electrochemical reduction of vitamin B(2) using linear sweep voltammetry on disposable carbon electrodes. The enhancement was observed only when dissolved oxygen was present. In model solutions the analytical signal was linear in the concentration range 6-150 ng/mL with a calculated limit of detection of 5 ng/mL (S/N = 3). This compared favorably with earlier work using a similar measurement approach--but in the absence of copper--in which the limit of detection was calculated to be 900 ng/mL. The effects of potential interferents commonly found in cereals were examined. In addition to signal attenuation by both sugar and starch (already reported), folic acid was found to increase (+6%) and iron to decrease (-11%) the analytical signal when present in the maximum concentration ratios, with respect to vitamin B(2), that are normally found in breakfast cereals. Nevertheless, the simplicity of the approach was potentially attractive for near-line quality control applications in manufacturing. The utility of the measurement approach was demonstrated by the addition of excess copper(II) sulfate to determine vitamin B(2) in aqueous extracts of breakfast cereals. The results agreed well with those provided by the cereal manufacturer who used an established HPLC method.

Determination of colour developing agents in photographic processing solutions using fixed-volume single-use sensors

An electrochemical method for the determination of colour developing agents in photographic processing solutions using single-use sensors is described. The sensor consists of two parts: the transducer, based on a screen-printed carbon (working and reference) and gold (counter) three-electrode configuration; and a sampler/electrochemical cell. The parts fit together to give a single-shot sampling and measurement device. The sensors were used to monitor the concentrations of the colour developing agent CD-4 (i.e. 4-(N-ethyl-N-2-hydroxyethyl)-2- methylphenylenediamine sulfate) in a photoprocessor. Comparison with HPLC data showed that there was a good correlation between the two methods (R2 = 0.97). The sensor method was more convenient to use than HPLC and enabled measurements to be carried out at the photoprocessor without need to send samples to a laboratory for analysis.