Thiolated DNA-Based Chemistry and Control in the Structure and Optical Properties of Plasmonic Nanoparticles with Ultrasmall Interior Nanogap

Abstract

The design, synthesis and control of plasmonic nanostructures, especially with ultrasmall plasmonically coupled nanogap (∼1 nm or smaller), are of significant interest and importance in chemistry, nanoscience, materials science, optics and nanobiotechnology. Here, we studied and established the thiolated DNA-based synthetic principles and methods in forming and controlling Au core-nanogap-Au shell structures [Au-nanobridged nanogap particles (Au-NNPs)] with various interior nanogap and Au shell structures. We found that differences in the binding affinities and modes among four different bases to Au core, DNA sequence, DNA grafting density and chemical reagents alter Au shell growth mechanism and interior nanogap-forming process on thiolated DNA-modified Au core. Importantly, poly A or poly C sequence creates a wider interior nanogap with a smoother Au shell, while poly T sequence results in a narrower interstitial interior gap with rougher Au shell, and on the basis of the electromagnetic field calculation and experimental results, we unraveled the relationships between the width of the interior plasmonic nanogap, Au shell structure, electromagnetic field and surface-enhanced Raman scattering. These principles and findings shown in this paper offer the fundamental basis for the thiolated DNA-based chemistry in forming and controlling metal nanostructures with ∼1 nm plasmonic gap and insight in the optical properties of the plasmonic NNPs, and these plasmonic nanogap structures are useful as strong and controllable optical signal-generating nanoprobes.

Applications of gold nanoparticles in medicine and therapy

“…166,167 While resonant nanostructures are certainly desirable for the ranostic applications, having the ability to tune the photo thermal effect of SERS probes while preserving their high SERS activity is critical to avoid unwanted heating during imaging. Oh et al 168 designed and synthesized plasmonic AuNPs with ultra small (typically, ∼1nm) interior gap using thiolated DNA and obtained the relationships between these noble metal nano gap structures and plasmonic signals from these structures. 168 In 2015, Tian et al 169 demonstrate bio enabled synthesis of a novel class of ultra-bright SERS probes with built-in and accessible electromagnetic hotspots formed by densely packed satellite NPs grown on a plasmonic core.…”

“…Oh et al 168 designed and synthesized plasmonic AuNPs with ultra small (typically, ∼1nm) interior gap using thiolated DNA and obtained the relationships between these noble metal nano gap structures and plasmonic signals from these structures. 168 In 2015, Tian et al 169 demonstrate bio enabled synthesis of a novel class of ultra-bright SERS probes with built-in and accessible electromagnetic hotspots formed by densely packed satellite NPs grown on a plasmonic core. 169 Through the rational choice of the shape of the core, the LSPR wavelength of Au superstructures was tuned to be either off or on-resonant with the NIR excitation without sacrificing their high SERS activity.…”

Facile Preparation of Ultrasmall Void Metallic Nanogap from Self‐Assembled Gold–Silica Core–Shell Nanoparticles Monolayer via Kinetic Control

“…[16,17] On the other hand, bottom-up approaches have utilized molecular DNA, block copolymers, and molecular ligands as gap-directing molecules. [18][19][20][21][22] These methods typically require delicate control over colloidal chemistry. Another concern associated with bottom-up approaches is that the resulting gap is either already fi lled with the gap-directing molecules or blocked by two metal layers and thus it is diffi cult for surrounding molecules to diffuse close to the nanogap.…”

“…Because of this limitation, to realize the benefi t of strong fi eld enhancement, reporter molecule such as fl uorescent molecule often needs to be served as gap-directing molecule during the preparation of nanogap structures. [ 19 ] Small nanogaps also happen to be randomly formed in metal nanoparticle aggregates. [ 23,24 ] However, one disadvantage is lack of reproducibility of the location and density of the aggregates with the nanogaps, which can be an issue for integration into reproducible large-scale fabrication.…”

Nanoantenna effect of surface-enhanced Raman scattering: managing light with plasmons at the nanometer scale

“…It has been generally acknowledged that the physical mechanism of SP gives the main contribution to the SERS enhancement [55]. In closely packed nanostructures, such as a dimer nanoparticle, SERS could reach the singlemolecule level due to the strong coupling of SP in nanogaps [7,[56][57][58]. Recently, even single molecules can be spectrally mapped by cutting-edge tip-enhanced Raman technique based on plasmon enhancement [59].…”