Quantitative investigation of the poly-adenine DNA dissociation from the surface of gold nanoparticles

Abstract

In recent years, poly adenine (polyA) DNA functionalized gold nanoparticles (AuNPs) free of modifications was fabricated with high density of DNA attachment and high hybridization ability similar to those of its thiolated counterpart. This nanoconjugate utilized poly adenine as an anchoring block for binding with the AuNPs surface thereby facilitated the appended recognition block a better upright conformation for hybridization, demonstrating its great potential to be a tunable plasmonic biosensor. It's one of the key points for any of the practical applications to maintaining stable conjugation between DNA oligonucleotides and gold nanoparticles under various experimental treatments. Thus, in this research, we designed a simple but sensitive fluorescence turn-on strategy to systematically investigate and quantified the dissociation of polyA DNA on gold nanoparticles in diverse experimental conditions. DNA desorbed spontaneously as a function of elevated temperature, ion strength, buffer pH, organic solvents and keeping time. What's more, evaluating this conjugate stability as affected by the length of its polyA anchor was another crucial aspect in our study. With the improved understanding from these results, we were able to control some of our experimental conditions to maintain a good stability of this kind of polyA DNA-AuNPs nanoconjugates.

Figure 1

Effect of temperature (B, C) and NaCl concentration (D) on the release of the polyA-DNAs into solution. Each sample also contained 5 mM HEPES, pH 7.6. (A) Schematic illustrating the fluorescence-based measurement of the released FAM-labeled DNA from the DNA−AuNPs. (B) Fraction of released DNA from polyA₁₀, polyA₂₀, polyA₃₀ DNA-AuNPs over a period of 10 min at different temperatures (55, 65, 75, 85 and 95 °C) (C) Fraction of released DNA from polyA₁₀, polyA₂₀, polyA₃₀ DNA-AuNPs over a period of 10, 20 and 30 min at 95 °C (D) Fractions of released DNA from polyA₂₀ DNA-AuNPs over a periods of 4, 6, 8 and 12 min at 95 °C in different concentration of NaCl.

Figure 2

Effect of pH on the release of the polyA (10, 20 and 30, respectively) DNAs into solution. The buffers (5 mM HEPES) were adjusted for pH 4, 7.4, 11 and 13.

Figure 3

Photographs of polyA (10, 20 and 30, respectively) DNA-functionalized AuNPs dispersed in various concentrations of organic solvents. DMF = dimethylformamide; DMSO = dimethyl sulfoxide; EG = ethylene glycol. Each sample also contained 5 mM HEPES, pH 7.4. (A) Photographs of polyA₁₀-DNA-functionalized AuNPs dispersed in various concentrations of organic solvents. (B) Photographs of polyA₂₀-DNA-functionalized AuNPs dispersed in various concentrations of organic solvents. (C) Photographs of polyA₃₀-DNA-functionalized AuNPs dispersed in various concentrations of organic solvents.

Figure 4

Effect of various concentration (40%, 80%) solvents on the release of the polyA₁₀, polyA₂₀, polyA₃₀-DNA into solution. Each sample also contained 5 mM HEPES, pH 7.6.

Figure 5

Dissociation of the three polyA₁₀, polyA₂₀, polyA₃₀ DNA from AuNPs surface as a function of DNA sequence, salt, EDTA (2 mM), temperature, and ethanol (80%). All samples contained 100 mM NaCl, pH 7.4. (A, B, C) Dissociation of the polyA₁₀ DNA, polyA₂₀ DNA and polyA₃₀ DNA from AuNPs surface at different storage conditions. (D) Comparison of the DNA desorption kinetics come from the 3 different kinds of DNA AuNPs conjugates. polyA₁₀ DNA−AuNPs (black block), polyA₂₀ DNA−AuNPs (red dot) and polyA₃₀ DNA−AuNPs (blue triangle) contained 100 mM NaCl, in 26 °C.