Synthesis, Optical Properties, and Multiplexed Raman Bio‐Imaging of Surface Roughness‐Controlled Nanobridged Nanogap Particles

Abstract

Plasmonic nanostructures are widely studied and used because of their useful size, shape, composition and assembled structure-based plasmonic properties. It is, however, highly challenging to precisely design, reproducibly synthesize and reliably utilize plasmonic nanostructures with enhanced optical properties. Here, we devise a facile synthetic method to generate Au surface roughness-controlled nanobridged nanogap particles (Au-RNNPs) with ultrasmall (≈1 nm) interior gap and tunable surface roughness in a highly controllable manner. Importantly, we found that particle surface roughness can be associated with and enhance the electromagnetic field inside the interior gap, and stronger nanogap-enhanced Raman scattering (NERS) signals can be generated from particles by increasing particle surface roughness. The finite-element method-based calculation results support and are matched well with the experimental results and suggest one needs to consider particle shape, nanogap and nanobridges simultaneously to understand and control the optical properties of this type of nanostructures. Finally, the potential of multiplexed Raman detection and imaging with RNNPs and the high-speed, high-resolution Raman bio-imaging of Au-RNNPs inside cells with a wide-field Raman imaging setup with liquid crystal tunable filter are demonstrated. Our results provide strategies and principles in designing and synthesizing plasmonically enhanced nanostructures and show potential for detecting and imaging Raman nanoprobes in a highly specific, sensitive and multiplexed manner.

Intracellular and Cellular Detection by SERS‐Active Plasmonic Nanostructures

“…To provide stable cellular signals and maximize the signal intensities, many types of nanogapped nanoparticles (NNPs) were designed. The groups of Nam and Lim developed Raman dye tagged core–shell nanostructures with uniformly confined intra‐nanogaps of about 1 nm tailored by DNA. The Raman signals of dyes tagged in the gap are greatly enhanced and allow for bioimaging under transient exposure times and low input power of the incident laser (Figure A) .…”

Quantitative Nanoplasmonics

“…Outer shell surface roughness also affects the electromagnetic field of the intra-nanogap and, hence, the optical response of the structures, thereby providing additional room for enhancement by readily controlling the roughness. 39 Nanocrevice particles with a conductive nanojunction are another type of plasmonically coupled structure with strong and controllable electromagnetic field. For Au–Ag hetero-nanostructures, salt-concentration-dependent kinetic control governs the structural morphology.…”

Plasmonic Nanogaps: From Fabrications to Optical Applications

“…Due to its large enhancement effect, nanogap‐based SERS technology had been widely applied for bioanalysis and cell imaging . Lim and co‐workers reported that the use of specific spacer sequence (T10) of oligonucleotides on the core DNA‐modified Au nanoparticles could lead to the formation of very narrow intra‐nanogap structures in spherical‐shape gold nanoparticles (Au‐NNPs) even in the presence of a large number of Raman reporters on core DNA modified AuNP (DNA‐AuNP) .…”

“…For targeting and multiplexed Raman‐based cell imaging, they selected two more Raman dyes to generate SERS‐sensitive Au‐NNPs ( Figure ). Moreover, Nam and co‐workers devised a facile synthetic method to generate Au surface roughness‐controlled nanobridged nanogap particles (Au‐RNNPs) with ultrasmall (≈1 nm) interior gap and tunable surface roughness in a highly controllable manner . The roughness of the particle surface and the number of nanobridges for Au‐RNNPs highly affect and enhance the electromagnetic field inside the interior nanogap and stronger Raman signals from particles.…”

“…The subwavelength “hot spots” with highly confined energy are easily generated in the gaps, resulting in the enhancement of EM fields by orders of magnitude. This intriguing capability was essential to enable applications in surface enhanced spectroscopy, sensing, imaging, nonlinear optics, optical trapping, and metamaterials . In view of the remarkable advantages and broad application prospects, tremendous efforts have been devoted to fabricate various nanogaps.…”