Cranfield University at Silsoe (1975-2008)
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Item Open Access Amperometric biosensor for formic acid in air(Elsevier, 2000-11-01) Sandström, K. J. Mattias; Newman, Jeffrey D.; Sunesson, Anna-Lena; Levina, Jan-Olof; Turner, Anthony P. F.The possibility of developing a simple, inexpensive and specific personal passive ”real-time” air sampler based on biosensor technology was investigated. Formic acid was used as a model substance. The sensor is based on the enzymatic reaction between formic acid and formate dehydrogenase with NAD+ as a cofactor and Meldola’s blue as mediator. An effective way to immobilise the enzyme, cofactor and Meldola’s blue on screen-printed electrodes was found to be in a mixture of glycerol and phosphate buffer covered with a gas-permeable membrane. When the sensor was introduced into an atmosphere containing formic acid, it gave a distinct and rapid amperometric response.Item Open Access Biotin–specific synthetic receptors prepared using molecular imprinti(Elsevier Science B.V., Amsterdam., 2004-02-16T00:00:00Z) Piletska, Elena V.; Piletsky, Sergey A.; Karim, K.; Terpetschnig, E.; Turner, Anthony P. F.The composition of new molecularly imprinted polymers (MIPs) specific for biotin was optimised using molecular modelling software. Three functional monomers: methacrylic acid (MAA), 2-(trifluoromethyl)acrylic acid (TFAA) and 2-acrylamido- 2-methyl-propanesulfonic acid (AMPSA), which demonstrated the highest binding scores with biotin, were tested on their ability to generate specific binding sites. The imprinted polymers were photografted to the surface of polystyrene microspheres in water. The affinity of the synthetic "receptor" sites was evaluated in binding experiments using horseradish peroxidase-labelled biotin. A good correlation was found between the modelling results and the performance of the materials in the template rebinding study. The dissociation constants for all MIPs were 1.4-16.8 nM, which is sufficient for most analytical applications where biotin is used as a label.Item Open Access Calibration methodology for mapping within-field crop variability using remote sensing(Elsevier Science, 2003-04) Wood, G. A.; Taylor, John C.; Godwin, R. J.A successful method of mapping within-field crop variability of shoot populations in wheat (Triticum aestivum) and barley (Hordeum vulgare L.) is demonstrated. The approach is extended to include a measure of green area index (GAI). These crop parameters and airborne remote sensing measures of the normalised difference vegetation index (NDVI) are shown to be linearly correlated. Measurements were made at key agronomic growth stages up to the period of anthesis and correlated using statistical linear regression based on a series of field calibration sites. Spatial averaging improves the estimation of the regression parameters and is best achieved by sub-sampling at each calibration site using three 0·25 m2 quadrats. Using the NDVI image to target the location of calibration sites, eight sites are shown to be sufficient, but they must be representative of the range in NDVI present in the field, and have a representative spatial distribution. Sampling the NDVI range is achieved by stratifying the NDVI image and then randomly selecting within each of the strata; ensuring a good spatial distribution is determined by visual interpretation of the image. Similarly, a block of adjacent fields can be successfully calibrated to provide multiple maps of within-field variability in each field using only eight points per block representative of the NDVI range and constraining the sampling to one calibration site per field. Compared to using 30 or more calibration sites, restricting samples to eight does not affect the estimation of the regression parameters as long as the criteria for selection outlined in this paper is adhered to. In repeated tests, the technique provided regression results with a value for the coefficient of determination of 0·7 in over 85% of cases. At farm scale, the results indicate an 80–90% probability of producing a map of within crop field variability with an accuracy of 75–99%. This approach provides a rapid tool for providing accurate and valuable management information in near real-time to the grower for better management and for immediate adoption in precision farming practices, and for determining variable rates of nitrogen, fungicide or plant growth regulators.Item Open Access Compatible measurements of volumetric soil water content using a neutron probe and Diviner 2000 after field calibration.(Blackwell Publishing Ltd., 2006-12-01T00:00:00Z) Burgess, Paul J.; Reinhard, Berend Richard; Pasturel, P.Field calibrations for a neutron probe and a capacitance sensor (Diviner 2000) for measuring the soil water content of a shrinking–swelling clay soil were substantially different from commonly used default values. Using our field calibrations, the two instruments estimated similar changes in the cumulative water content of a soil profile (0–1 m depth) over one growing seaItem Open Access Compost liquor bioremediation using waste materials as biofiltration media.(Elsevier, 2005-03) Savage, A. J.; Tyrrel, Sean F.Compost liquor results from the percolation of precipitation through composting waste; the release of liquids from high moisture content feedstocks; and as a result of runoff from hard surfaces and machinery. This research aimed to establish the potential for waste materials to act as media for low-cost compost liquor biofilters. Six types of potential biofilter media were packed into experimental biofilters (1 m long x 0.11 m diameter) and irrigated with compost liquor (organic loading rate of 0.6 kg/m3/d) for three months. The pH, BOD5, NH3/NH4+, and phytotoxicity of the effluent was monitored regularly. Natural, organic materials (oversize, compost and wood mulch) performed best, when compared to synthetic materials such as polystyrene packaging or inert materials such as broken brick. On average, the best media achieved 78% removal of both BOD5 and ammoniacal nitrogen during the study period. Although significant improvements in liquor quality were achieved, the effluent remained heavily polluted.Item Open Access Custom synthesis of molecular imprinted polymers for biotechnological application: preparation of a polymer selective for tylosin(Elsevier Science B.V., Amsterdam., 2004-02-16T00:00:00Z) Piletsky, Sergey A.; Piletska, Elena V.; Karim, K.; Foster, G.; Legge, C.; Turner, Anthony P. F.A molecularly imprinted polymer (MIP) selective for tylosin was designed and synthesised using a computational method (MIP “dialling”). In re-binding experiments the MIP demonstrated high affinity for tylosin in aqueous solutions and in organic solvents. The synthesised polymer was tested for re-binding with the template and related metabolites such as tylactone, narbomycin and picromycin. The HPLC analysis showed that the computationally designed polymer is specific and capable of separating the template from its structural analogues. The MIP was capable of recovering tylosin from broth samples. The polymer capacity for tylosin was estimated as 6.4 mg/g for MIP, which was suitable for practical application and tylosin recovery from broth samples. Among the advantages of this was the possibility to adsorb tylosin from a complex media with easy removal of oils and other impurities which are present in significant quantities, which can create problems for its chromatographic purification procedure. The MIP “dialling” procedure can have a general significance for the fast preparation of specific adsorbents for biotechnological appliItem Open Access Detection of TP53 mutation using a portable Surface Plasmon Resonance DNA-based biosensor(Elsevier, 2005-02-02T17:36:22Z) Jiang, Tieshan; Minunni, Maria E.; Wilson, P. K.; Zhang, Jian; Turner, Anthony P. F.; Mascini, MarcoA DNA-based Surface Plasmon Resonance (SPR) biosensor has been developed for the detection of TP53 mutation using the inexpensive and commercially available instrument, SPREETATM SPR-EVM-BT, from Texas Instruments. A direct immobilization procedure, based on the coupling of thiol-derivatised oligonucleotide probes (Probe-C6-SH) to bare gold sensor surfaces, was optimized using synthetic oligonucleotides. Hybridization reactions between the immobilized probe and a short sequence (26 mer) complementary, non-complementary and one point mutation DNA were then investigated. The main analytical parameters of the sensor system were studied in detail including selectivity, sensitivity, reproducibility and analysis time. Finally, the sensor system was successfully applied to polymerase chain reaction (PCR) amplified real samples, DNA extracted from both normal, wild type, (Jurkat) and mutated (Molt 4), carrying the mutation at codon 248 of the TP53 cell lines. The results obtained demonstrate that the DNA-based SPR biosensor was able to distinguish sequences present in the various samples that differ only by one base and hence it appears to be a strong candidate technique for the detection of gene mutation.Item Open Access Developing strategies for spatially variable nitrogen application in cereals II: wheat(Elsevier Science, 2003-04) Welsh, J. P.; Wood, G. A.; Godwin, R. J.; Taylor, John C.; Earl, R.; Blackmore, S.; Knight, S. M.For precision agriculture to provide both economic and environmental benefits over conventional farm practice, management strategies must be developed to accommodate the spatial variability in crop performance that occurs within fields. Experiments were established in crops of winter barley (Hordeum vulgare L.) over three seasons. The aim of which was to evaluate a set of variable rate nitrogen strategies and examining the spatial variation in crop response to applied N. The optimum N application rate varied from 90 to in excess of 160 kg [N] ha−1 in different parts of the field, which supports the case for applying spatially variable rates of N. This, however, is highly dependent on seasonal variations, e.g. the quantity and distribution of rainfall and the effect that this has on soil moisture deficits and crop growth. Estimates of yield potential, produced from either historic yield data or shoot density maps derived from airborne digital photographic images, were used to divide experimental strips into management zones. These zones were then managed according to two N application strategies. The results from the historic yield approach, based on 3 yr of yield data, were inconsistent, and it was concluded that that this approach, which is currently the most practical commercial system, does not provide a suitable basis for varying N rates. The shoot density approach, however, offered considerably greater potential as it takes account of variation in the current crop. Using this approach, it was found that applying additional N to areas with a low shoot population and reducing N to areas with a high shoot population resulted in an average strategy benefit of up to 0·36 t ha−1 compared with standard farm practice.Item Open Access Developing Strategies for spatially variable nitrogen application in cereals, I: Winter barley(Elsevier Science, 2003-04) Welsh, J. P.; Wood, G. A.; Godwin, R. J.; Taylor, John C.; Earl, R.; Blackmore, S.; Knight, S. M.For precision agriculture to provide both economic and environmental benefits over conventional farm practice, management strategies must be developed to accommodate the spatial variability in crop performance that occurs within fields. Experiments were established in crops of winter barley (Hordeum vulgare L.) over three seasons. The aim of which was to evaluate a set of variable rate nitrogen strategies and examining the spatial variation in crop response to applied N. The optimum N application rate varied from 90 to in excess of 160 kg [N] ha−1 in different parts of the field, which supports the case for applying spatially variable rates of N. This, however, is highly dependent on seasonal variations, e.g. the quantity and distribution of rainfall and the effect that this has on soil moisture deficits and crop growth. Estimates of yield potential, produced from either historic yield data or shoot density maps derived from airborne digital photographic images, were used to divide experimental strips into management zones. These zones were then managed according to two N application strategies. The results from the historic yield approach, based on 3 yr of yield data, were inconsistent, and it was concluded that that this approach, which is currently the most practical commercial system, does not provide a suitable basis for varying N rates. The shoot density approach, however, offered considerably greater potential as it takes account of variation in the current crop. Using this approach, it was found that applying additional N to areas with a low shoot population and reducing N to areas with a high shoot population resulted in an average strategy benefit of up to 0·36 t ha−1 compared with standard farm practice.Item Open Access Development and application of a soil classification-based conceptual catchment- scale hydrological model(Elsevier Science B.V., Amsterdam., 2005-10-01T00:00:00Z) Marechal, David; Holman, Ian P.A conceptual, continuous, daily, semi distributed catchment-scale rainfall- runoff model that has the potential to be ultimately used in ungauged catchments is described. The Catchment Resources and Soil Hydrology (CRASH) model is developed from the basis that the transformation of rainfall into simulated river discharge can be parameterised using pre-existing national datasets of soil, land use and weather; and that the spatial variability in soil properties and land use are important to the hydrological response of a catchment and should be incorporated into the catchment representation. Both infiltration- excess and saturation-excess runoff mechanisms are simulated, with water movement through each soil layer simulated using a capacitance approach limited according to layer physical properties. The hydrological linkage between the response unit and catchment is parameterised using the existing national Hydrology of Soil Types (HOST) classification. The HOST classification groups all UK soil types into one of 29 hydrological classes for which nationally calibrated values of Base Flow Index and Standard Percentage Runoff are provided. CRASH has been calibrated and validated for three catchments in England with contrasting soil characteristics and meteorological conditions. The model was successful at simulating time series and flow duration curves in all catchments during the calibration and validation periods. The next development stage will be to test CRASH for a large number of catchments covering a wider range of soils, land uses and meteorological conditions, in order to derive a set of regionalised model parameters based upon the HOST classification. The successful cross-scale linkage between water movement through the response unit and the catchment-scale hydrological response using the HOST classification, which incorporates the scale effects between plot and catchment, suggests that such national soil hydrological classifications may provide a sound and consistent framework for hydrological modelling in both gauged and ungauged catchments which should be extended to other regions.Item Open Access The distribution of peatland in Europe.(Jointly by International Mire Conservation Group and International Peat Society, 2006) Montanarella, Luca; Jones, Robert J. A.; Hiederer, RolandThis paper derives the distribution of peatland in Europe as the extent of peat and peat-topped soils indicated by soil databases. The data sources were the 1:1,000,000 European Soil Database (v1.0) and a data set of organic carbon content (%) for the topsoils of Europe at 1km x 1km resolution that was recently published in map form. The strong influences of vegetation and land use on soil organic carbon (OC) content were taken into account in computing the 1km (OC) data set, as was the influence of temperature. The areas of peat and peat-topped soils estimated from the European Soil Database are generally in close agreement with those obtained using the Map of OC in Topsoils of Europe. The results reveal a strong northern bias in the distribution of organic soils across Europe. Almost one-third of the peatland resource of Europe is in Finland, and more than a quarter is in Sweden. The remainder is in Poland, the UK, Norway, Germany, Ireland, Estonia, Latvia, The Netherlands and France. Small areas of peat and peat-topped soils also occur in Lithuania, Hungary, Denmark and the Czech Republic. For most European countries, the distribution of peat and peat-topped soils is probably more accurately portrayed by the Map of OC in Topsoils of Europe than by the European Soil Map and Database. Such baseline data are important for the conservation of peat and for making much more precise estimates of carbon stocks in topsoil than have been possible hitherto. The results are also relevant to the planning of effective soil protection measures at European level.Item Open Access An Economic analysis of the potential for precision farming in UK cereal production(Elsevier Science, 2003-04) Godwin, R. J.; Richards, Terence E.; Wood, G. A.; Welsh, J. P.; Knight, S. M.The results from alternative spatial nitrogen application studies are analysed in economic terms and compared to the costs of precision farming hardware, software and other services for cereal crops in the UK. At current prices, the benefits of variable rate application of nitrogen exceed the returns from a uniform application by an average of £22 ha−1 The cost of the precision farming systems range from £5 to £18 ha−1 depending upon the system chosen for an area of 250 ha. The benefits outweigh the associated costs for cereal farms in excess of 80 ha for the lowest price system to 200–300 ha for the more sophisticated systems. The scale of benefits obtained depends upon the magnitude of the response to the treatment and the proportion of the field that will respond. To be cost effective, a farmed area of 250 ha of cereals, where 30% of the area will respond to variable treatment, requires an increase in crop yield in the responsive areas of between 0·25 and 1.00 t ha−1 (at £65 t−1) for the basic and most expensive precision farming systems, respectively.Item Open Access The electrochemistry of the ferri/ferrocyanide couple at a calix [4]resorcinarenetetrathiol-modified gold electrode as a study of novel electrode modifying coatings for use within electro-analytical sensors(Elsevier Science B.V., Amsterdam., 2003-06-05T00:00:00Z) Collyer, Stuart D.; Davis, Frank; Lucke, Andrew; Stirling, Charles J. M.; Higson, Seamus P. J.The electrochemistry of the ferri/ferrocyanide redox couple has been studied at Au electrodes modified with calix[4]resorcinarenetetrathiol. Cyclic voltammetry in Fe(CN)63- solutions yields three separate pairs of faradaic peaks. Evidence is given for these redox couples corresponding to the reduction of Fe(CN)63- and the subsequent re-oxidation of Fe(CN)64- in three differing steric arrangements. One pair of peaks suggest that when the Fe(CN)63- ion resides within the calix [4]resorcinarene bowl, electron transport is facilitated by the calix [4]resorcinarene acting as a charge transfer mediator; in this arrangement the activation energy is found to be lowered by ~24kJmol-1. Another pair of peaks is thought to correspond to the reduction of Fe(CN)63- as it approaches the Au electrode by packing itself in-between adjacent calix[4]resorcinarene molecules. The third pair of redox peaks is attributed to the reduction and subsequent re- oxidation of Fe(CN)63-/Fe(CN)64- when the ion resides above a saturated calix [4]resorcinarene coating; in this case the activation energy was raised by ~45kJmol-1. FTIR spectroscopy of calix[4]resorcinarene-coated Au electrodes and calix[4]resorcinarene-coated Au electrodes exposed to Fe(CN)63- lends further support to this argument, by demonstrating that the Fe(CN)63- ion resides within at least two and possibly three differing environments. Calix[4]resorcinarene modified electrodes previously exposed to ferricyanide lose the calix [4]resorcinarene coating together with a surface layer of gold when subsequently scanned in a phosphate buffer. It therefore appears that the calix [4]resorcinarene/Fe(CN)63- association is stronger than the Au binding to the underlying glass material.Item Open Access Evaluation of probabilistic modelling approaches against data on leaching of isoproturon through undisturbed lysimeters(Elsevier, 2004-11-15) Beulke, Sabine; Brown, Colin D.; Dubus, Igor G.; Fryer, Christopher J.; Walker, AllanThis study evaluated probabilistic modelling approaches against data on leaching of isoproturon through two contrasting soil types. Leaching through undisturbed lysimeters from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) was investigated in seven replicates. The variability of soil properties and of sorption and degradation of isoproturon was estimated by taking 6-14 samples within the areas of lysimeter extraction in the field. Normal distributions were assigned to Koc and DT50 and a large number of values for these two parameters were sampled from each distribution. Parameter values were used to simulate movement of isoproturon through the lysimeters with the preferential flow model MACRO. Uncertainty in output distributions was compared with the variability of measured data. A constrained probabilistic assessment varying only degradation and sorption properties was sufficient to match the observed variability in cumulative leaching from the coarse-textured Wick soil (CV = 79%). Variation of pesticide properties alone could not match observed variability in cumulative leaching from the structured Hodnet soil (CV = 61%) and variability in a number of soil properties was incorporated. For both soils, constrained probabilistic approaches where only the top few most sensitive model inputs were varied were sufficient to match or exceed observed variability.Item Open Access Evaluation of simple hand-held Mechanical systems for harvesting tea (Camellia Sinensis)(Cambridge University Press, 2006-04-01T00:00:00Z) Burgess, Paul J.; Carr, M. K. V.; Mizambwa, F. C. S.; Nixon, D. J.; Lugusi, J.; Kimambo, E. I.Over an eight-year period, harvesting methods based on simple mechanical aids (blade and shear) were evaluated against hand harvesting on mature morphologically contrasting tea clones in Southern Tanzania. The effects of shear step height (5-32 mm) and the harvest interval (1.8-4.2 phyllochrons) were also examined. Except in the year following pruning, large annual yields (5.7- 7.9 t dry tea ha[minus sign]1) were obtained by hand harvesting at intervals of two phyllochrons. For clones K35 (large shoots) and T207 (small shoots), the mean harvested shoot weights were equivalent to three unfurled leaves and a terminal bud. The proportions of broken shoots (40-48 %) and coarse material (4- 6 %) were both relatively high. Using a blade resulted in similar yields to hand harvesting from K35 but larger yields from T207 (+13 %). The yield increase from clone T207 was associated with the harvest of more shoots and heavier shoots, smaller increases in canopy height, and a higher proportion (7-9 %) of coarse material compared to hand harvesting. On bushes, which had been harvested by hand for two years following pruning, using flat shears (no step) supported on the tea canopy resulted, over a three year period, in yields 8-14 % less than those obtained by hand harvesting and, for clone K35, a reduction in the leaf area index to below 5. The development of a larger leaf area index is made possible by adding a step to the shear. However, since annual yields were reduced by 40-50 kg ha[minus sign]1 per mm increase in step height, the step should be the minimum necessary to maintain long-term bush productivity. As mean shoot weights following shear harvesting were about 13 % below those obtained by hand harvesting, there is scope, when using shears, to extend the harvest interval from 2 to 2.5 phyllochrons.Item Open Access A foliar disease model for use in wheat disease management decision support systems.(Blackwell Publishing Ltd., 2005-10-01T00:00:00Z) Audsley, Eric; Milne, Alice E.; Paveley, NeilA model of winter wheat foliar disease is described, parameterised and tested for Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Erysiphe graminis (powdery mildew) and Puccinia triticina (brown rust). The model estimates diseaseinduced green area loss, and can be coupled with a wheat canopy model, in order to estimate remaining light intercepting green tissue, and hence the capacity for resource capture. The model differs from those reported by other workers in three respects. Firstly, variables (such as weather, host resistance and inoculum pressure) which affect disease risk are integrated in their effect on disease progress. The agronomic and meteorological data called for are restricted to those commonly available to growers by their own observations and from meteorological service networks. Secondly, field observations during the growing season can be used both to correct current estimates of disease severity and modify parameters which determine predicted severity. Thirdly, pathogen growth and symptom expression are modeled to allow the effects of fungicides to be accounted for as protectant activity (reducing infections which occur postapplication) and eradicant activity (reducing growth of pre-symptomatic infections). The model was tested against data from a wide range of sites and varieties, and was shown to predict the expected level of disease sufficiently accurately to support fungicide treatment decisions.Item Open Access A framework for integrating flood defence and biodiversity in washlands in England(Jrbm, 2005-01-01T00:00:00Z) Morris, Joe; Hess, Tim M.Concerns about increased flood risk and loss of biodiversity in lowland areas, coupled with changing priorities in the countryside have drawn attention to the potential contribution that managed washlands can make to improved flood management, habitats and wildlife. Following a review of research literature, a survey of flood managers and conservation officers, and an evaluation of selected case sites in England, a framework to help integrate potential flood management and biodiversity opportunities was constructed. This framework consists of three components, namely: a Hydraulic classification which categorises washlands according to degree of hydraulic control; a Habitat classification which captures attributes of washland hydrology that define the type of existing or potential habitats; and, a Menu of Interventions to “engineer” or manage particular flooding and soil wetness regimes and thereby better exploit habitat potential. Washlands were also categorised by main type of benefit whether this is flood management, conservation, or in the case of integratedwashland, a balance of the two. The advantages of alternative administrative and funding arrangements for washlands, whether land acquisition or annual payment to existing land owners, were also explored. It was concluded that the classification of washland flooding and water level regimes can help to define habitat potential. It can also help to guide hydraulic engineering and management actions that can be taken to realise this potential. Although there is potential synergy between flooding and biodiversity under some flood regimes, biodiversity benefits mainly depend on the management of water regimes following flood events. There is a clear need to “join up” hitherto fragmenteItem Open Access Immunosensor for okadaic acid using quartz crystal microbalance(Elsevier Science B.V., Amsterdam., 2002-10-23T00:00:00Z) Tang, Alice X. J.; Pravda, Miloslav; Guilbault, George G.; Piletsky, Sergey A.; Turner, Anthony P. F.An immunosensor for the determination of okadaic acid (OA) using a quartz crystal microbalance (QCM) was developed and optimised in standard solutions. Several coupling techniques, protein A, protein G and polyethylenimine (PEI) with glutaraldehyde (GA) cross-linking, were investigated for the determination of okadaic acid and a very good result was obtained with PEI coupling. With the PEI coupling method, the optimisation of incubation time for the activation of PEI on the crystal surface using GA, the effect of the dilution factor of OA-BSA conjugate and the amount of antibody on crystal frequency were studied. Different molar ratios (4:1, 14:1, 30:1) of OA to bovine serum albumin (BSA) for the conjugation were examined and the results using ELISA and a QCM showed that a ratio of 14:1 was slightly better than the other two. The strong attachment of the cross-linked complex to the gold surface resulted in an excellent storage lifetime of 38 days. However, the detection limit (1.9 µg/ml) and the sensitivity of the sensor were not satisfactory. Significant improvement of the performance of the device was obtained by incorporating an antibody-BSA hydrogel. Initial results showed that the minimum amount of analyte detectable and the sensitivity of the device were improved by 524 and 80 fold, respectivelyItem Open Access Improved procedures for immobilisation of oligonucleotides on gold-coated piezoelectric quartz crystals(Elsevier, 2002-12) Tombelli, S.; Mascini, Marco; Turner, Anthony P. F.The high sensitivity and specificity of DNA hybridisation techniques makes them powerful tools for environmental or clinical analysis. This work describes the development of a DNA piezoelectric biosensor for the detection of the hybridisation reaction. Attention was focused on the choice of the coating chemistry that could be used for the immobilisation of oligonucleotides onto the gold surface of the quartz crystal. Four immobilisation procedures were tested and compared considering the amount of immobilised probe, the extent of the hybridisation reaction, the possibility of regeneration and the absence of non-specific adsorption. All the experiments were performed with oligonucleotides of 25 bases (probe, target and non-complementary oligonucleotide).The four coating methods were all based on the use of self-assembled monolayers. Three of them employed the interaction between streptavidin and biotin for the immobilisation of a biotinylated probe.Results indicated that immobilisation of a biotinylated probe on streptavidin linked to a layer of carboxylated dextran provides higher sensitivity for the detection of the hybridisation reaction, absence of non-specific adsorption and a higher stability with respect to the regeneration step.Item Open Access Influence of kinetic sorption and diffusion on pesticide movement through aggregated soils(Elsevier, 2004-11) Beulke, Sabine; Brown, Colin D.; Fryer, Christopher J.; van Beinum, WendyLaboratory studies were carried out to investigate solute leaching at different times from application in relation to temperature and initial soil moisture. Aggregates of a heavy clay soil were treated with a non-interactive solute (bromide) and the herbicides chlorotoluron, isoproturon and triasulfuron. The soil was incubated at 90% field capacity and either 5 or 15oC. The influence of application to initially dry and initially wet aggregates on the behaviour of isoproturon was also investigated. At intervals, samples were either leached in small columns, centrifuged to characterise the fraction of chemical available in pore water under natural moisture conditions or extracted with organic solvents to assess total residues in soil. Bromide concentrations in leachate and in pore water extracted by centrifugation were constant with time. In contrast, availability for leaching and concentration in pore water of the herbicides decreased with increasing time from application in soil incubated at 15oC. The effect of residence time was much smaller at 5 than at 15oC. At the higher temperature, pesticide concentrations in leachate and pore water declined faster than would be expected from degradation alone, probably due to slow diffusion of the pesticides into soil aggregates where they are less available for leaching and/or slow sorption-desorption. The faster decline in availability for leaching at 15 than at 5oC was attributed to faster degradation of the readily available fraction. There was no significant influence of initial soil moisture on either the leaching behaviour of isoproturon or its availability in soil water.
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