A novel one-step electrochemical method for DNA detection is described. The procedure utilizes a reaction catalyzed by a peroxidase-mimicking DNAzyme to produce a product, which forms an insoluble precipitation layer on the surface of an electrode. A rationally designed forward primer, conjugated with a peroxidase DNAzyme complementary sequence at its 5'-end, is used for PCR amplification of target DNA. As a result, the DNAzyme sequence is produced by amplification only when the target DNA is present in the sample. The PCR product is then subjected to the precipitation reaction on the electrode surface using an electrolyte assay buffer containing 4-chloronaphthol, hydrogen peroxide, ferrocenemethanol, hemin, and 5'-lambdaexonuclease. Finally, analysis is carried out using Faradaic impedance spectroscopy. The impedance value was found to greatly increase when target DNA is present owing to the formation of a precipitation layer on the electrode surface caused by the catalytic action of the DNAzyme. In contrast, no impedance increase is observed when a control sample not containing target DNA is utilized. By employing this strategy, target DNA from Chlamydia trachomatis was reliably detected within a 10 min period following precipitation without the need for complicated secondary procedures. This effort has led to the development of a highly convenient electrochemical one-step method for DNA detection that utilizes a peroxidase-mimicking DNAzyme, which is specifically designed to undergo amplification during PCR of target DNA. (C) 2011 Elsevier B.V. All rights reserved.