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Fluorescent microsphere labels
A biotinylated SPE surface with bound Extravidin and alkaline phosphatase. The enzyme reaction yields a phenolic product that is detected with linear scan voltammetry.
Biotin coats for electrodes As the interest in multianalyte sensors increases, so does the desire to find simple, rapid, and versatile methods of distributing biomolecules on electrode surfaces. Biotin monolayers have been deposited using photopatterning, but this approach requires sophisticated equipment. Electrodeposition is a less expensive alternative, but the biotinylated polymer coatings produced this way can have slow response times, low sensitivities, or nonspecific binding. Now, Benoit Limoges, Murielle Dequaire, and Chantal Degrand of the Universite Blaise Pascal de Clermont-Ferrand (France) describe a new approach that deposits a monolayer of biotin on disposable screen-printed electrodes (SPEs). These electrodes are made with a conductive carbon ink of graphite particles embedded in a polystyrene binder. They have a double-layer capacitance of 1.6 uF cm"2 (~20 times lower than that of a glassy carbon electrode) better response over a wide pH
Ring in the elements Since its introduction in 198S, there has been only one report of using cavity ringdown spectroscopy (CRDS) lor trace elemental analysis. Count one more. (i. P. Miller and colleagues at Mississippi State University report preliminary experiments combining CRDS with a graphite furnace to measure lead with a detection limit of 1 pg—sllghtly better than the typical detection limit for electrothermal atomic absorption spectrometry. Hie experimental setup consisted of a transversely heated graphite furnace mounted inside the cavity so that the laser beam could pass through the center of the graphite tube. Measurements
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range, and lower detection limits, according to the researchers. The biotin is attached using a previously published procedure in which the diazonation of a biotinylated aniline derivative occurs in ice-cold acidic water, and the solution is transferred to an electrochemical cell where the cathodic functionalization of the SPE takes place at 4 °C. Then the biotinylated SPEs are allowed to react with Extravidin—a form of avidin that has little nonspecific binding. To test the performance of the electrodes, the researchers incubated them with biotinylated alkaline phosphatase (AP) and carried out enzyme reactions on the SPE surface, generating a phenolic product that was quantified by anionic linear scan voltammetry. In the first run, the peak current, t_ a, was 8.35 uA in the presence of Extravidin and biotinylated AP, but
