Silver nanoparticle-oligonucleotide conjugates based on DNA with triple cyclic disulfide moieties

Abstract

We report a new strategy for preparing silver nanoparticle-oligonucleotide conjugates that are based upon DNA with cyclic disulfide-anchoring groups. These particles are extremely stable and can withstand NaCl concentrations up to 1.0 M. When silver nanoparticles functionalized with complementary sequences are combined, they assemble to form DNA-linked nanoparticle networks. This assembly process is reversible with heating and is associated with a red shifting of the particle surface plasmon resonance and a concomitant color change from yellow to pale red. Analogous to the oligonucleotide-functionalized gold nanoparticles, these particles also exhibit highly cooperative binding properties with extremely sharp melting transitions. This work is an important step toward using silver nanoparticle-oligonucleotide conjugates for a variety of purposes, including molecular diagnostic labels, synthons in programmable materials synthesis approaches, and functional components for nanoelectronic and plasmonic devices.

Figure 1

(A) Schematic illustration of the hybridization of two complementary DNA-Ag NPs. (B) UV-vis spectra of unmodified Ag NPs (black line), unhybridized DNA-Ag NPs (blue line), and hybridized DNA-Ag NPs (red line). Note that the wavelength at which the maximum of the extinction of Ag NPs is obtained remains the same after DNA-functionalization. After hybridization, however, the band of DNA-Ag NPs broadens and red-shifts significantly from 410 nm to 560 nm. (C) Colorimetric change responsible for the assembly process of DNA-Ag NPs. The intense yellow color of the unhybridized Ag NPs (C1) turns to pale red (C2) as the particle aggregation proceeds. Heating of (C2), however, results in the return of the solution color to yellow (C1).

Figure 2

The melting transition for the DNA-Ag NP aggregates as monitored by the extinction of the Ag nanoparticles at 410 nm as a function of temperature (T_m = 46.5 °C). The concentration of nanoparticles is 1 nM (total). Note that the melting temperature is 46.5 °C and the melting transition is extremely sharp (FWHM = 2.4 °C), which is comparable to that of DNA-Au NP aggregates.

Figure 3

(A) Melting transitions for DNA-Ag NP aggregates (20 nm in diameter) at various salt concentrations: 0.15 M, 0.30 M, 0.50 M and 0.70 M. The concentration of Ag NPs is 1 nM (total). (B) A plot of T_m as a function of salt concentration.