Dynamic Plasmonic Platform To Investigate the Correlation between Far-Field Optical Response and SERS Signal of Analytes

Abstract

The design of surface-enhanced Raman spectroscopy (SERS) platforms based on the coupling between plasmonic nanostructures and stimuli-responsive polymers has attracted considerable interest over the past decades for the detection of a wide range of analytes, including pollutants and biological molecules. However, the SERS intensity of analytes trapped inside smart hybrid nanoplatforms is subject to important fluctuations because of the spatial and spectral variation of the plasmonic near-field enhancement (i.e., its dependence with the distance to the nanoparticle surface and with the localized surface plasmon resonance). Such fluctuations may impair interpretation and quantification in sensing devices. In this paper, we investigate the influence of the plasmonic near-field profile upon the Raman signal intensity of analytes trapped inside thermoresponsive polymer-coated gold nanoarrays. For this, well-defined plasmonic arrays (nanosquares and nanocylinders) were modified by poly( N -isopropylacrylamide) (PNIPAM) brushes using surface-initiated atom-transfer radical polymerization. Molecular probes were trapped inside these Au@PNIPAM nanostructures by simple physisorption or by covalent grafting at the end of PNIPAM brushes, using click chemistry. The SERS spectra of molecular probes were studied along various heating/cooling cycles, demonstrating a strong correlation between SERS intensities and near-field spectral profile of underlying nanoparticles, as confirmed by simulations based on the finite difference time domain method. Thermoresponsive plasmonic devices thus provide an ideal dynamic SERS platform to investigate the influence of the near-field plasmonic profile upon the SERS response of analytes.

Highly Heterogeneous Polarization and Solvation of Gold Nanoparticles in Aqueous Electrolytes

“…M etal nanoparticles (NPs), in particular gold nanoparticles (AuNPs), have been extensively studied as promising materials for various applications in biomedicine, 1−5 plasmonic resonance, 6,7 and NP-mediated catalysis. 8−14 AuNPs have useful physicochemical properties because of their high surface-area-to-volume ratio as well as distinctive surface morphologies and chemical compositions, which can be very different from those of bulk or cluster states.…”

Actively Tunable Collective Localized Surface Plasmons by Responsive Hydrogel Membrane

“…We demonstrate that the temperature modulation or exchanging the solvent allows for reversible shifting of plasmonic resonances in the near infrared part of the spectrum by up to 150 nm, which exceeds the spectral width of the resonance as low as 13 nm and allows its complete switching “on” and “off.” The potential capabilities for biosensing with the tethered configuration employing a hydrogel that can be post‐modified with protein ligands are assessed for the refractometric localized surface plasmon resonance biosensors, where a figure of merit as high as 29 was observed. The plasmonic architectures with on‐demand tunable optical properties also hold potential to be employed as active plasmonic substrates in other biosensor modalities taking advantage of plasmonically amplified optical spectroscopy and in miniature machines . For instance, the tunable plasmonic wavelength may find its applications in multiplexed plasmon‐enhanced fluorescence sensing or for the fine‐tuning of surface‐enhanced Raman spectroscopy enhancement for specific vibration bands.…”

“…Refractive index of a collapsed hydrogel membrane was estimated as n h = 1.46, that of the membrane swollen in water as n h = 1.34 (refractive index of solvent n s = 1.331 at 700 nm and T = 25 °C), and after swelling in ethanol as n h = 1.36 (refractive index of water n s = 1.359 at 700 nm and T = 20 °C). These values were obtained assuming the volumetric swelling ratio in water of 8 (same material showed swelling in each direction of about 2 as observed for micro‐disks) and by relating this swelling ratio to data measured for similar thin hydrogel films with same volume swelling ratio …”

Highly Heterogeneous Polarization and Solvation of Gold Nanoparticles in Aqueous Electrolytes

“…gold nanoparticle, polarization, image charge, ion-specific effect, metal-liquid interface, molecular dynamics simulation Metal nanoparticles (NPs), in particular gold nanoparticles (AuNPs) have been extensively studied as promising materials for various applications in biomedicine, 1-5 plasmonic resonance, 6,7 and NP-mediated catalysis. [8][9][10][11][12][13][14] AuNPs have useful physicochemical properties because of their high surface-area-to-volume ratio as well as distinctive surface morphologies and chemical compositions, which can be very different from those of bulk or cluster states.…”