A transcriptionally amplified DNA probe assay with ligatable probes and immunochemical detection.

Transcriptionally amplified DNA probes are valuable tools in the development of sensitive nucleic acid-based diagnostic assays. Here we describe a model assay using a novel oligonucleotide hairpin probe that encodes a T7 RNA polymerase promoter. The hairpin probe and an adjacently hybridizing biotinylated capture probe were hybridized to target DNA and the duplex was captured onto streptavidin-coated magnetic particles. After ligation of the immobilized probes, which served to maintain specificity, the hairpin probe was transcribed by T7 RNA polymerase. The amplified RNA product was hybridized to the capture probe and bound to the streptavidin-coated magnetic particles. The immobilized heteroduplex was detected with an antibody-alkaline phosphatase conjugate specific for DNA:RNA hybrids, and the chemiluminescent substrate adamantyl-1,2-dioxetane phenyl phosphate. Ten attomoles of target DNA could be detected in a background of 5 micrograms of unrelated DNA. The chemiluminescent immunoassay was as sensitive as radioactive detection of specific product after gel electrophoresis.