Rapid visual detection of Mycobacterium tuberculosis DNA using gold nanoparticles

Tuberculosis (TB) is one of the world's deadliest infections caused by Mycobacterium tuberculosis (MTB). Though curable, the disease goes undetected in early stages owing to the lack of rapid, simple, cost-effective, and sensitive detection methods. In this investigation, we describe a procedure which is superior, more sensitive, and easier to handle, as compared to the previously reported, nanoparticle-based visual colorimetric assays for rapid detection of TB DNA, after its PCR amplification. This assay employs plasmonic gold nanoparticles (GNP) as a colorimetric agent and ethanol to promote aggregation of GNPs, thereby specifically detecting the amplified MTB DNA. An unambiguous response was achieved within 3 min after adding the DNA amplicon to the reaction tube. This conclusion was supported by spectroscopic data. The assay is sensitive up to ∼340 femtomole levels of MTB DNA, which was amplified using 0.125 ng μL^-1 of the MTB DNA template. Thus, the technique developed here may be employed as a sensitive screening tool for early diagnosis of TB infection and is valuable for low-resource settings in remote areas, because of its simplicity. This ethanol-based visual TB DNA detection method is more sensitive, and fool-proof as compared to the commonly used salt-based colorimetric TB DNA assays, to the best of our knowledge.