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

Nanooptics of Plasmonic Nanomatryoshkas: Shrinking the Size of a Core–Shell Junction to Subnanometer

“…The strong coupling between these higher-order modes (mode 1 and 2) of the NMs to light is primarily attributed to phaseretardation effects due to their relatively large particle size. 45 The weak electric field enhancements in the gap region imply a rather weak plasmon coupling between the core and the shell, and therefore the far-field optical spectrum of NMs (25,125,150) nm is here dominated by the scattering spectrum of the outer Au shell.…”

“…NMs with dimensional parameters (25,125,150) nm (i, Figure 2B) were synthesized using a procedure reported elsewhere. 43 Briefly, 50 nm-sized citrate Au NPs were prepared by adding sodium citrate into hydrogen tetrachloroaurate trihydrate (HAuCl 4 ) aqueous solution.…”

“…In most of the present work, the dielectric spacer between the core and the shell will be either a SiO 2 layer or a monolayer of 1,4-BDT molecules (the case of the 4-MBT molecules will be quoted specifically). Previous results have indicated that classical electromagnetic (25,125,150) nm with a gap size of 100 nm and with SiO 2 space layer; (ii) (40,55,68) nm with a gap size of 15 nm and with SiO 2 spacer layer; (iii) (10, 10.7, 25) nm with a gap size of 0.7 nm and with 1,4-BDT spacer layer. (A) Geometrical illustration, (B) TEM/SEM images, (C) experimentally measured extinction spectra, and (D) calculated extinction spectra using classical electromagnetic theory for the NMs (i−iii).…”

“…9−12 Recently, there have been increasing interests in the experimental and theoretical investigations of plasmonic "nanomatryoshka" (NM) particles, 13−23 which consists of a spherical metallic core surrounded by a concentric metallic shell separated by a dielectric layer (see Figure 1A), due to its significant potential in multiplexed biosensing and bioimaging application. 24,25 The interior "nanogaps", that is, the core−shell separation, can be easily tuned by controlling the thickness of the dielectric spacer, consequently controlling the extent of the coupling and induced near-field enhancement between the core and shell. This phenomenon has been well explained by classical electromagnetic theory, which predicts strong electric field enhancements in the nanogaps region.…”

“…30−35 For a NM with core−shell separations below 0.4 nm, calculations from time-dependent density functional theory (TDDFT) have predicted pronounced tunneling across the nanogap, which significantly modifies the absorption cross-section and the local electric field enhancements. 22 More importantly, advances in the synthesis of NMs with precise and uniform subnanometer gaps provide a better platform for experimental investigation of quantum plasmonic effects, 17,25,36,37 compared to typical nanoparticle dimer structures fabricated by various state-of-the-art techniques including high-resolution electron-beam lithography, 30 electron-beam induced manipulation, 26 dual AFM tip approaching, 28 and dropcasting. 27,31 In this Letter, we present a comprehensive investigation of the optical properties of NMs with different nanogap widths ranging from 100 nm down to the subnanometer regime.…”