Microscopic Differentiation of Plasmonic Nanoparticles for the Ratiometric Read-out of Target DNA

The development of highly sensitive and rapid methods for detecting DNA is of critical importance. Here, we describe a strategy for the digital detection of target DNA at the femto-molar level. Individual DNA molecules were encoded with a single gold nanorod (AuNR), separated and enriched by magnetic immune-separation. The coding gold nanorods were then de-hybridized and dispersed into a gold nanosphere (AuNS) solution at a certain concentration, and both gold nanoparticles were immobilized on glass slides for dark-field microscopic imaging. Using an in-house Matlab program, the concentration of the target DNA was calculated based on the ratio of the coding gold nanorods to gold nanospheres. By combining the coding of individual biomolecules with a single gold nanorod and the use of gold nanospheres as an internal standard, a method for the rapid and accurate digital detection of target DNA to the femto-molar level was developed.