AuNPs amplified magnetophoretic effect for colorimetric detection of nucleic acid

Colorimetric assay for detection of nucleic acid offers superior simplicity for point-of-care applications. However, the limit of detection (LOD) is usually at nM level in many colorimetric assays, which is insufficient for disease diagnosis or pathogen identifications. Here we report a colorimetric detection of nucleic acids based on gold nanoparticles (AuNPs) amplified magnetophoretic effect. The assay was conducted in two steps. In the first step, the present target DNA molecules link magnetic microparticles (MMPs) and AuNPs, and the linked AuNPs can be subsequently collected after magnetic attraction and heat treatment. In the second step, the collected AuNPs linked a pair of MMPs and polymer microparticles (PMPs), forming MMPs-AuNPs-PMPs. Thus, by applying an external magnetic field that pulls the linked MMPs-AuNPs-PMPs to the sidewall, magnetophoretic effect renders a change of solution color from opaque to transparent reflecting the quantity of the target DNA molecules. Our results demonstrate the LOD reaches 45 amol (1 pM in 45 μl) by spectrometry and 2.25 fmol (50 pM in 45 μl) by naked eyes. This method is tens to hundreds times more sensitive as compared with other colorimetric detections such as AuNPs aggregation or lateral flow test strip, with great potential for applications in low resource settings.