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Assessing DNA damage Oxidative damage to DNA has been linked to various diseases, and progressive diseases such as Alzheimer's and Parkinson's may be the result of an accumulation of unrepaired DNA damage to neurons. S. P. Markey and Dmitry B. Naritsin of the National Institute of Mental Health have developed a technique that assesses DNA oxidative damage by quantifying thymidine glycol residues, a well-known product of the reaction of hydroxyl radical with thymidine. The goal of the research was to develop a method with sufficient sensitivity to analyze the 1- to 10-ug DNA samples typically obtained from biological experiments. The researchers used alkaline cleavage and borodeuteride reduction to release 2-methylglycerate from thymidine glycol in DNA; the 2-methylglycerate was then derivatized to form a combined
Screen-printed biosensors for environmental applications T-shirts, sweatshirts, bumper stickers, biosensors—what do these things have in common? They can all be screen-printed. Joseph Wang and co-workers at New Mexico State University, the U.S. Environmental Protection Agency (Las Vegas) , Dublin City University (Ireland), and the Universidade de Sao Paulo (Brazil) screen-printed tyrosinase-containing carbon-ink electrodes onto an alumina ceramic plate. The thick film was cured for 2 h at 110 °C, and the resulting disposable electrodes were used to quantitate pesticides and herbicides that inhibit tyrosinase function. Electrodes with different amounts of tyrosinase were used for amperometric measurements of 5 x 10~5 M catechol (substrate) and 1 x 10"5 M diethyldithiocarbamate (inhibitor). The sensor responded within 1 min to the substrate and pesticide additions, indicating that the biocatalytic and inhibition activities
pentafluorobenzyl-fert-butyldimethylsilyl (PFB-TBDMS) derivative that was analyzed by GC/electron capture negativeionization MS. They found that the PFB-TBDM! derivative exhibits excellent chromatographic and Chromatograms for (a) blank, (b) a 156-fmol thymine glycol detection standard, and (c) a 10-^g DNA sample. (Adapted with permission ties and they from Academic Press.) obtained a detection limit of 41 amol injected on column was present in a sample of salmon sperm They also found that the background DiN/\ that had autooxidized during storlevel of thymidine glycol detected in age in a refrigerated aqueous solution. freshlv dissolved calf thymus DNA was Studies using the method for assessment 11 7 + 0 3 x 11~6 mol/mol lhymiiine end of DNA damage in various biological systhat an increased level of thymidine glvcol tems are in progress. {Anall Biochem. (71 2 ± 14 3 x 10~6 mollmol lhymidine^ 1996,241,35-41)
were maintained despite the 2-h curing time. The sensors were then calibrated for submillimolar concentrations of diethyldithiocarbamate, thiourea, benzoic acid, 2,4-dichlorophenoxyacetic acid, and 4,6-dinitro-o-cresol. The plots were not linear and curved significantly at high concentrations. A potential of -0.2 V
yielded the best detection of the catechol and the inhibitors, and the low potential minimized interference from constituents of the water sample. When the authors attempted to reuse the screenprinted strips, sensitivity decreased by as much as 79%, although such signal decreases are not surprising for irreversible inhibition reactions. To demonstrate the use of the electrodes for environmental applications, the researchers spiked untreated water from the Rio Grande River with increasing amounts of diethyldithiocarbamate. The strips responded rapidly to the incremental additions even though no electrolyte WAs added. Despite the success in measuring the spiked samples the electrode response would be nonspecific in comCalibration plot of a water sample from the Rio Grande plex environmental matriRiver with catechol as the substrate and sodium ces (Talanta 1996 43 diethyldithiocarbamate as the inhibitor. (Adapted with 1903-07) permission from Elsevier Science.) Analytical Chemistry News & Features, December 1, 1996 711 A
