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Enzyme-catalyzed polymer transformation with electrochemical ac impedance detection has been employed for the measurement of urea and creatinine in serum samples. A polymer, based on poly(methylvinyl ether)/maleic anhydride modified by esterification with n-octanol, which is stable at pH 7.4 and which is transformed rapidly in response to alkaline pH changes, was linked to enzymatic reactions between urease and urea or creatinine deiminase and creatinine to produce a disposable sensor system. The polymer was screen-printed onto interdigitated screen-printed carbon electrodes and the electrodes overlaid with absorbent pads containing the relevant enzyme. Application of serum samples, 'spiked' with either urea or creatinine, resulted in rapid polymer transformation, and resultant changes in the capacitance of the polymer-coated electrodes were analyte-concentration dependent. Additional information on the mechanisms of polymer transformation was obtained from dynamic quartz crystal microbalance measurements.

A novel sensor approach based on ac impedance measurement of capacitance changes produced during enzyme-catalyzed dissolution of polymer coatings on electrodes, leading to a 4 orders of magnitude change in capacitance, is described. Electrodes were coated with an enteric polymer material, Eudragit S 100, which is based on methyl methacrylate, and dissolution was exemplified by utilizing the catalytic action of the enzyme urease. The resulting alkaline pH change caused dissolution of the polymer film with a consequent large increase in capacitance. A mechanism for polymer breakdown is proposed which has been validated experimentally using both ac impedance measurements and electron microscopy. The large changes in capacitance that are apparent using this technique allow much greater sensitivity of measurement than, for example, potentiometric electrodes. The potential broad clinical analytical application of this technique is demonstrated in this report by application to urea measurement and to enzyme immunoassay. Urea measurement between 2 and 100 mM has been achieved with a change in response over this concentration range by over 4 orders of magnitude. We have taken account of both the effect of protein adsorption on the surface of the polymer-coated and bare electrodes and the effect of buffer capacity when carrying out these measurements in buffered solutions containing 8% (w/v) protein and have demonstrated that the method should allow simple, interference-free measurement of urea in serum and whole blood. In addition, both competitive and noncompetitive enzyme immunoassays for human IgG based on the use of urease-antibody conjugates are reported. Human IgG, or goat anti-human IgG (Fab specific), were immobilized covalently onto cellulosic membranes via a diamine spacer group and the membranes placed over enteric polymer-coated electrodes. Specific measurement of IgG in both formats was achieved over the concentration range 0.0001-100 [[micro]gram] [[[micro]molar].sup.-1]. The performances of the impedance-based enzyme immunoassays were compared directly with identical assays employing spectrophotometric detection.

The article shares possible remedies for dealing with the problem with seedlings associated with Streptocarpus, including hybridizing. It suggests transplanting seed into a different soil if the ion concentration of soil is too acidic and cutting 1/3 to 1/2 of the tip of the very first leaf of the plant to stimulate the production of new leaves. Other suggestions are to try the use of diluted liquid iron in the soil and performing an ion concentration test on seeds with abscission lines.

Introduces a series of articles on energetic materials and deformation behaviour of structural materials at high strain rates.

The article focuses on un-sterilizing potting mix. The author says that most of the soil mixes used for growing Streptocarpus are sterilized, resulting in the elimination of insects, seeds and soil microorganisms, such as bacteria and fungi. He explains that this practice is done to clear out organisms that may be harmful to the plants. He notes that members of the African Violet (AV) Association of Australia have never sterilized prepared potting mixes, instead, they only pasteurize it.