Robust raspberry-like metallo-dielectric nanoclusters of critical sizes as SERS substrates

Abstract

Raspberry-like nano-objects made of large plasmonic satellites (>10 nm) covering a central dielectric particle have many potential applications as photonic materials, superlenses and (bio-) sensors, but their synthesis remains challenging. Herein, we show how to build stable and robust raspberry-like nano-systems with close-packed satellites, by combining monodisperse silica particles (80 or 100 nm diameter) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10-50 nm). The spectral characteristics of their associated plasmonic resonances (wavelength, linewidth, extinction cross-section) and the electromagnetic coupling between satellites were observed using the spatial modulation spectroscopy technique and interpreted through a numerical model. The composite nano-objects exhibit numerous hot spots at satellite junctions, resulting in excellent surface-enhanced Raman scattering (SERS) performance. The SERS efficiency of the raspberry-like clusters is highly dependent on their structure.

Extending Surface‐Enhanced Raman Spectroscopy to Liquids Using Shell‐Isolated Plasmonic Superstructures

“…Le Beulze et al. already showed that using this method, significant SERS‐enhancement can be obtained with 10–50 nm citrate‐stabilized Ag and Au NPs on 80–100 nm SiO 2 spheres . However, we believe that increasing the SiO 2 sphere size will have a beneficial effect: larger plasmonic nanoparticles can be used, increasing the signal enhancement by creating stronger hot spots.…”

“…Numerous methods have already been explored, including synthesis of plasmonic nanoparticles with intrinsic hotspots, self‐assembly of plasmonic nanoparticles into complex superstructures and assembly of plasmonic nanoparticles onto larger SiO 2 spheres . Of these methods, adsorption of Au NPs onto large SiO 2 spheres may well be the most promising of all.…”

“…Numerous methods have already been explored, including synthesis of plasmonic nanoparticles with intrinsic hotspots, [15] self-assembly of plasmonic nanoparticles into complex super-structures [16] and assembly of plasmonic nanoparticles onto larger SiO 2 spheres. [17] Of these methods, adsorption of Au NPs onto large SiO 2 spheres may well be the most promising of all. This method is not only facile in preparation (simply mixing dispersions of Au NP and SiO 2 spheres with appropriate surface chemistry), it also providese asy tunability by simply adjusting Au NP size and/or SiO 2 sphere size, which can alter plasmon resonance wavelength or colloidal stability.L eB eulze et al already showed that using this method, significant SERS-enhancement can be obtained with 10-50 nm citrate-stabilized Ag and Au NPs on 80-100 nm SiO 2 spheres.…”

“…This method is not only facile in preparation (simply mixing dispersions of Au NP and SiO 2 spheres with appropriate surface chemistry), it also providese asy tunability by simply adjusting Au NP size and/or SiO 2 sphere size, which can alter plasmon resonance wavelength or colloidal stability.L eB eulze et al already showed that using this method, significant SERS-enhancement can be obtained with 10-50 nm citrate-stabilized Ag and Au NPs on 80-100 nm SiO 2 spheres. [17] However,w e believe that increasing the SiO 2 sphere size will have ab eneficial effect:l argerp lasmonic nanoparticles can be used, increasing the signal enhancement by creatings trongerh ot spots. However,s edimentation rate of these plasmonic Au/SiO 2 superstructures needs to be taken into account,a st his will limit the time scale of experimentso nr eactions under investigation.…”

Optothermal response of a single silicon nanotip

“…In this work, we directly 56 measure the optical response of a single silicon nanotip by 57 spatial modulation spectroscopy (SMS) [20,21]. This original 58 technique has been previously used to detect individual zero-59 dimensional (0D) absorbing nano-objects and measure their 60 absolute optical extinction spectra [22][23][24][25][26][27][28]. SMS has also been 61 successfully exploited to investigate one-dimensional (1D) 62 cylindrical nano-objects such as single metal nanowires and 63 carbon nanotubes (with length much larger and diameter much 64 smaller than the size of the focused light beam), providing 65 access to their optical response [21,29,30].…”