Ultrasensitive Label-Free DNA Detection Using Cantilever of Atomic Force Microscope Amplified by Gold Nanoparticles

A cantilever sensor in a dynamic model based on the signals amplified by gold nanoparticles (Au- NPs) was applied to the ultrasensitive, label-free detection of a DNA sequence. A thiolated probe DNA (12 mer) was self-assembled onto a gold film (Au-film) coated cantilever via a strong Au-S bond. Another thiolated probe DNA (12 mer) was conjugated preliminarily with Au-NPs (mean diameter= 15 nm). Sandwich hybridization occurred between the two probes DNA and target DNA (24 mer). The Au-NPs were confirmed to have been captured on the cantilever surface mainly by hybridization reactions from the changes in the resonant frequency and SEM images of the cantilever under a variety of conditions. To determine the concentration of the target DNA quantitatively, the Au-NPs were used as "mass enhancers" to amplify the frequency change of the cantilever. With the signals amplified by the Au-NPs, the detection limit reached 0.034 fM. The selectivity of the sensor is also discussed. The high sensitivity and selectivity of this novel cantilever sensor makes it a useful alternative to the DNA hybridization assays currently used. © 2016 American Scientific Publishers.