Rapid colorimetric quantification of PCR-amplified DNA.

A diagnostic system for rapid colorimetric quantification of the initial amount of DNA template amplified by the polymerase chain reaction is described. The method is based on co-amplification of target DNA with a cloned DNA fragment, in which a lac operator sequence has been introduced by in vitro mutagenesis. The in vitro-amplified material is immobilized on magnetic beads using the biotin-streptavidin system, and the ratio of target DNA to cloned mutated DNA can be determined using a fusion protein consisting of the Escherichia coli LacI repressor and beta-galactosidase. This method for quantitative detection of immobilized amplified nucleic acids is well adapted for rapid automated or semi-automated assays. Here, we show that it can be used to detect and quantify Plasmodium falciparum genomic DNA in clinical samples.