Dual colorimetric strategy for specific DNA detection by nicking endonuclease-assisted gold nanoparticle signal amplification.

The continuous spread of invasive alien species, as zebra mussel (Dreissena polymorpha), is a major global concern and it is urgent to stop it. Early stages of an invasion are crucial and challenging; however, detection tools based on environmental DNA analysis are promising alternatives. We present an alternative DNA target amplification strategy for signal enhancement followed by dual-mode colorimetric naked eye and optical smartphone analysis for the early detection of zebra mussel environmental DNA. Target amplification was designed based on the nicking endonuclease probe cleavage upon probe and complementary target hybridization. The cleaved/intact probe interacts with DNA-modified nanoparticles for colorimetric detection. We have demonstrated that enzyme amplification strategy enhanced 12-fold the sensitivity by naked eye detection, achieving a detection limit of ~8 nM (4.48×10 copies) in controlled conditions, whereas target in complex environmental samples allowed the detection of 22.5 nM (1.26×10 copies). Competitive assays also showed that the system can discriminate specific zebra mussel DNA sequences from other DNA sequences. Additionally, smartphone analysis for DNA quantification further improved the sensitivity of its detection by 130-fold, more than 2 orders of magnitude, when applied to environmental samples. The limit of detection to 0.17 nM (9.52×10 copies) is based on RGB coordinates, which is especially relevant to monitor early aggregation stages, being more accurate and reducing naked eye detection subjectivity. DNA extracted from zebra mussel meat, zebra mussel contaminated river water, and non-contaminated river water samples were successfully tested. Dual-mode colorimetric detection is useful in field analysis without the need for expensive laboratory equipment.