Light-Mediated Directed Placement of Different DNA Sequences on Single Gold Nanoparticles

Abstract

This paper describes the light-directed functionalization of anisotropic gold nanoparticles with different thiolated-DNA oligomer (oligo) sequences. The starting nanoconstructs are gold nanostars (AuNS) uniformly grafted with one oligo sequence that are then exposed to fs-laser pulses at the plasmon resonance of the branches. The excitation selectively cleaves Au-S bonds at the tips of the branches to create vacant areas for functionalization with a different thiolated oligo sequence. Nanoconstructs synthesized by this approach present one oligo sequence on the AuNS body and branches and a different sequence at the tips. This process enables the formation of nanoparticle superstructures consisting of AuNS cores and small Au satellite nanoparticles at controlled locations after DNA hybridization. Our strategy enables selective oligo presentation at the single-particle level and opens prospects for sophisticated design of nanoscale assemblies that are important in a wide range of biological applications.

Figure 1.. Simulations of near-field enhancement of AuNS from 820-nm light irradiation.

(a) UV-Vis absorbance spectra of bulk AuNS solution (normalized to highest peak). (b-c) TEM images of AuNS with (b) one and (c) two long branches. (d-e) FDTD simulations show the near-field enhancement of plasmonic gold nanostars is unevenly distributed among branches when irradiated at the LSP of the bulk solution, which leads to selective tip DNA replacement.

Figure 2.. Higher laser power and longer irradiation times increase DNA release from AuNS.

As laser power (0.0, 0.3, 0.5, 0.7, or 0.9 W/cm²) and exposure time (4 or 10 s) increases, more DNA releases from the AuNS. P-values were calculated using a T-test. All samples had p-values <0.05 in comparison to non-irradiated DNA1@AuNS (0% release).

Figure 3.. Irradiated DNA1@AuNS add DNA2 strands to the surface through a second round of functionalization.

DNA1@AuNS were irradiated at 0, 0.3, 0.5, 0.7 or 0.9 W/cm² to release DNA1 from the surface of AuNS. The particles then went through a second round of functionalization in a 0.6 M [Na⁺] solution for 2 h to add DNA2 to the vacant spaces. p-values were calculated using a t-test. All samples had p-values < 0.01 compared to non-irradiated DNA1@AuNS (0.0 W/cm²).

Figure 4.. DNA4@AuNP_5-nm hybridize to DNA2 on AuNS.

(a) Scheme of DNA2, DNA3, and DNA4 hybridization. (b-e) TEM images of DNA4@spheres hybridized to (b) DNA1@AuNS (DNA1@AuNS), (c) irradiated DNA1@AuNS (0.5 W/cm² for 4 s) followed by a second round of functionalization to place DNA2 at the tips and keep DNA1 at the body (DNA1_Body⁻DNA2_Tips@AuNS), (d) irradiated DNA2@AuNS (0.5 W/cm² for 4 s) followed by a second round of functionalization to place DNA1 at the tips and keep DNA2 at the body (DNA2_Body⁻DNA1_Tips@AuNS), and (e) DNA2@AuNS.

Scheme 1.. DNA replacement on tips of AuNS branches.

DNA1 (grey) releases from the surface upon irradiation, leaving space at the tips for DNA2 (red) to conjugate.