Interior Nanogaps Research Articles

Thiolated DNA-based chemistry and control in the structure and optical properties of plasmonic nanoparticles with ultrasmall interior nanogap.

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.

Bimetallic nano-mushrooms with DNA-mediated interior nanogaps for high-efficiency SERS signal amplification

Uniform silver-containing metal nanostructures with well-defined nanogaps hold great promise for ultrasensitive surface-enhanced Raman scattering (SERS) analyses. Nevertheless, the direct synthesis of such nanostructures with strong and stable SERS signals remains extremely challenging. Here, we report a DNA-mediated approach for the direct synthesis of gold-silver nano-mushrooms with interior nanogaps. The SERS intensities of these nano-mushrooms were critically dependent on the area of the nanogap between the gold head and the silver cap. We found that the formation of nanogaps was finely tunable by controlling the surface density of 6-carboxy-X-rhodamine (ROX) labeled single-stranded DNA (ssDNA) on the gold nanoparticles. We obtained nano-mushrooms in high yield with a high SERS signal enhancement factor of similar to 1.0 x 10(9), much higher than that for Au-Ag nanostructures without nanogaps. Measurements for single nano-mushrooms show that these structures have both sensitive and reproducible SERS signals.

Gold nanostructures encoded by non-fluorescent small molecules in polyA-mediated nanogaps as universal SERS nanotags for recognizing various bioactive molecules

Surface-enhanced Raman scattering (SERS) has recently been used to design novel nanoprobes called “SERS tags” which hold great promise for the fields of biosensing and nanomedicine. More recent advances have shed new light on the synthesis of uniform nanostructures with interior nanogaps for stable SERS enhancement. However, producing interior nanogap-based SERS nanotags directly and controllably with strong and stable multiplex SERS signals as well as developing a multiplex analytical platform to recognize different types of bioactive molecules still remain highly challenging. To address this challenge, we herein develop a novel approach for the direct synthesis of nanogap-based universal SERS nanotags by mediating poly-adenine (polyA) and encoding non-fluorescent small molecules. The universal nanotags were then functionalized by different types of biological probes and used as SERS nanoprobes to recognize various bioactive molecules. To the best of our knowledge, this is the first example of using SERS nanotags to develop a simultaneous multianalysis platform for all of the major types of bioactive analytes, including nucleic acids, proteins and small molecules. Furthermore, the nanotags show great promise for fluorescence-SERS bimodal bioanalysis and bioimaging.

DNA-Mediated Wirelike Clusters of Silver Nanoparticles: An Ultrasensitive SERS Substrate

Stable metal nanoclusters (NCs) with uniform interior nanogaps reproducibly offer a highly robust substrate for surface-enhanced Raman scattering (SERS) because of the presence of abundant hot spots on their surface. The synthesis of such an SERS substrate by a simple route is a challenging task. Here, we have synthesized a highly stable wirelike cluster of silver nanoparticles (Ag-NPs) with an interparticle gap of ~1.7 ± 0.2 nm using deoxyribonucleic acid (DNA) as the template by exploiting an easy and inexpensive chemical route. The red shift in the surface plasmon resonance (SPR) band of Ag-NCs compared to SPR of a single Ag-NP confirms the strong interplasmonic interaction. Methylene Blue (MB) is used as a representative Raman probe to study the SERS effect of the NCs. The SERS measurements reveal that uniform, reproducible, and strong Raman signals were observed up to the single-molecule level. The intensity of the Raman signal is not highly dependent on the polarization of the excitation laser. The DNA-based Ag-NCs as a substrate show better isotropic behavior for their SERS intensity compared to the dimer, as confirmed from both the experimental and theoretical simulation results. We believe that in the future the DNA-based Ag-NCs might be useful as a potential SERS substrate for ultrasensitive trace detection, biomolecular assays, NP-based photothermal therapeutics, and a few other technologically important fields.

Facile synthesis of Au–Ag core–shell nanoparticles with uniform sub-2.5 nm interior nanogaps

A facile method was established to fabricate uniform nanogaps between a Au core and a Au-Ag alloy shell. The size of nanogaps is controllable due to fast dissolution of AgCl and AgBr in CTAB and the crystal growth of the shell on a designed template. These Au-Ag core-shell nanoparticles with uniform sub-2.5 nm interior nanogaps can be potentially used for various applications.