Facile and Controllable Loading of Single-Stranded DNA on Gold Nanoparticles

A facile strategy of loading thiolated single-stranded DNA (ss-DNA) on gold nanoparticles (NPs) has been developed. The gold NPs stabilized by nonionic fluorosurfactant (i.e., Zonyl FSN) are simply mixed with the thiolated ssDNA in the presence of NaCl (up to 1.0 M), and the ssDNA−NP conjugates are attained after an incubation of 2 h. The loading density of the ssDNA is controlled by the salt concentration in the immobilization solution. The FSN capping layer inhibits effectively the nonspecific adsorption of nucleobases on the NPs but allows for rapid attachment of the thiolated ssDNA through the sulfur−gold linkage, which may lead to an upright orientation of the immobilized ssDNA. The maximum loading density of the ssDNA obtained in 1.0 M NaCl is sensitive to several factors, such as the type of the spacer, the length of the ssDNA strands, and the NP size. The hybridization behavior of the ssDNA−NP conjugates with complementary ssDNA in solution was examined. For the conjugates of 13 nm-diameter NPs, the hybridization efficiency can reach ∼60% when the surface density of the ssDNA on the gold NP is lower than ∼15 pmol/cm2. As the ssDNA probes are more densely packed on the NPs, the hybridization efficiency drops consequently.