Ultrasensitive DNA Detection with Hydrodynamic Separation of Plasmonic Nanoparticles and Isothermal Amplification

Nucleic acid based assays are routinely used to detect diseases and monitor medical treatment. Here, we demonstrated a novel approach for colorimetric DNA detection using plasmonic gold nanoparticles (AuNPs) as hydrodynamic separators coupled with differential centrifugation. This approach relies upon the change in the sedimentation rate of AuNPs when conjugated to DNA amplicons. Isothermal nucleic acid amplification results in the formation of unique DNA amplicons that is large enough to prevent the sedimentation of conjugated AuNPs at a specific centrifugal force. In contrast, free nanoparticles are readily centrifuged and the solution color changes to colorless, enabling accurate and quantitative detection of the targeted DNA. This approach was challenged for the detection of sdfI gene of Salmonella. The decline of the red color intensity of AuNPs was linear to the concentration of the targeted DNA from 1.2 x 10(1) copies/ml to 1.2 x 10(7) copies/ml and the detection limit was as low as 120 copies/ml (S/N = 3). This simple platform could be used to establish inexpensive and sensitive assays for clinical and in-field diagnostic applications.