Colorimetric Detection of Loop-Mediated Isothermal Amplification Reaction by Using Hydroxy Naphthol Blue

Loop-mediated isothermal amplification (LAMP), a novel gene amplification method, enables the synthesis of larger amounts of both DNA and a visible byproduct--namely, magnesium pyrophosphate--without thermal cycling. A positive reaction is indicated by the turbidity of the reaction solution or the color change after adding an intercalating dye to the reaction solution, but the use of such dyes has certain limitations. Hydroxy naphthol blue (HNB), a metal indicator for calcium and a colorimetric reagent for alkaline earth metal ions, was used for a new colorimetric assay of the LAMP reaction. Preaddition of 120 microM HNB to the LAMP reaction solution did not inhibit amplification efficiency. A positive…