AFM-Nano Manipulation of Plasmonic Molecules Used as “Nano-Lens” to Enhance Raman of Individual Nano-Objects

Abstract

This paper explores the enhancement of Raman signals using individual nano-plasmonic structures and demonstrates the possibility to obtain controlled gold plasmonic nanostructures by atomic force microscopy (AFM) manipulation under a confocal Raman device. By manipulating the gold nanoparticles (Nps) while monitoring them using a confocal microscope, it is possible to generate individual nano- structures, plasmonic molecules not accessible currently by lithography at these nanometer scales. This flexible approach allows us to tune plasmonic resonance of the nanostructures, to generate localized hot spots and to circumvent the effects of strong electric near field gradients intrinsic to Tip Enhanced Raman Spectroscopy (TERS) or Surface Enhanced Raman Spectroscopy (SERS) experiments. The inter Np distances and symmetry of the plasmonic molecules in interaction with other individual nano-objects control the resonance conditions of the assemblies and the enhancement of their Raman responses. This paper shows also how some plasmonic structures generate localized nanometric areas with high electric field magnitude without strong gradient. These last plasmonic molecules may be used as "nano-lenses" tunable in wavelength and able to enhance Raman signals of neighbored nano-object. The positioning of one individual probed nano-object in the spatial area defined by the nano-lens becomes then very non-restrictive, contrary to TERS experiments where the spacing distance between tip and sample is crucial. The experimental flexibility obtained in these approaches is illustrated here by the enhanced Raman scatterings of carbon nanotube.

Application of Raman Spectroscopy in Biomedical Diagnostics

“…This phenomenon is particularly important in terms of provision of unambiguous analyte quantification as the enhancement should be highly reproducible while it is necessary to optimize SERS efficiency in relation to Plasmon excitation conditions [28]. For example, the SERS signal is directly related to the excitation wavelength and Raman scattering wavenumber [28][29][30][31][32][33][34][35][36] or the coupling between nanostructures [37][38][39]. Furthermore, aggregation of Au nanowires is less likely than in the case of colloidal Au NPs.…”

Plasmonics and its Applications

“…In the second and last part, the discussed topics are devoted to chemistry and sensing, such as surface-enhanced fluorescence, surface-enhanced Raman scattering (SERS), sum-frequency generation (SFG) spectroscopy, and electrocatalysis by using plasmonics [34,35,36,37,38,39,40]. Concerning the surface-enhanced fluorescence, Lu et al numerically demonstrated a high enhancement effect of the fluorescence signal obtained with a hybrid metal-dielectric nano-aperture antenna consisting of silicon and gold layers [34].…”

“…In this review, the recent advances in this topic of metal-dielectric micro/nano-resonators for SERS are exposed [36]. Furthermore, D’Orlando et al showed the feasibility to carry out and control nanostructures of gold nanoparticles, which can be seen as plasmonic molecules whose optical resonances are tuned by modifying the shape, symmetry, and interparticle distances with an AFM (Atomic Force Microscope) device coupled with an optical spectrometer [37]. To complete the sensing part, Han et al presented a short review on plasmonic biosensing based on the design of nanovoids in thin films by reviewing resonance modes, materials, and hybrid functions using simultaneously electrical conductivity [38].…”

Nanoscale Spatial Resolution in Far-Field Raman Imaging Using Hyperspectral Unmixing in Combination with Positivity Constrained Super-Resolution

“…In addition, the spectral response of the sample material may get distorted by the plasmonic interaction, often in an intricate and nonlinear fashion, which makes chemical analysis of such data challenging. 7,8…”

“…In addition, the spectral response of the sample material may get distorted by the plasmonic interaction, often in an intricate and nonlinear fashion, which makes chemical analysis of such data challenging. 7,8 Purely numerical approaches to resolution enhancement come without these drawbacks. Significant resolution enhancement has been achieved using super-resolution image restoration (SRIR) on single band/channel Raman images, [9][10][11][12] which have been improved using a multiband/-channel approach.…”