Photochemistry at the Surface of Gold Nanoprisms from Surface-Enhanced Raman Scattering Blinking

Abstract

In this work, we investigate the optical properties of triangular gold nanoprisms synthesized following a one-pot chemical process and using triethylene glycol (TREG) and polyvinylpyrrolidone (PVP) as solvent and capping agents. The nanoprisms sustain a strong localized surface plasmon resonance (LSPR) which is exploited in surface-enhanced Raman scattering (SERS) by the PVP and TREG molecules present at the nanoparticle surface. The work is focused on the temporal fluctuations of the SERS signal. The assignment of the observed Raman features is based on density functional theory calculations, performed for various interaction states between the PVP or the TREG molecules and the gold surface, in a simple model system. The SERS blinking is analyzed quantitatively using the autocorrelation of spectrally selected temporal SERS traces. We also use SERS covariance maps in order to investigate the cross-correlation between the relevant Raman features. We show that the fluctuations of the PVP and TREG SERS signals are not random. We found that the Raman features associated with the CO stretching vibrations are fingerprints of the interaction between the organic molecules and the nanoparticle surface. In particular, we observe quasi-periodic adsorption/desorption events of the PVP molecules that reveal their dynamical interaction with the gold surface. From the SERS covariance maps, we also point out correlations between the TREG and PVP signals which we interpret as occasional exchange of the two molecular species. The dependence of the SERS blinking on the detuning between the Raman excitation and the surface plasmon resonance is also investigated. We show that the optical excitation plays an important role in the photoinduced chemical processes that occur close to the nanoparticle surface.

Detection of the conformational changes of Discosoma red fluorescent proteins adhered on silver nanoparticles-based nanocomposites via surface-enhanced Raman scattering

“…Finally, either some of the desorbed proteins re-adsorb on the plasmonic substrate or the still adhered ones flip back to their initial configuration, even though with a lower SERS intensity ( figure 8(c)). Such photoinduced desorption/re-adsorption process have already been discussed in the literature [80]. Under non-resonant excitation the SERS signal and its blinking disappear ( figure 4(b)).…”

“…In addition, because of the SERS blinking, the intensity of the Raman features strongly fluctuates, which is another reason for the discrepancy between the measured SERS intensities and the DFT-calculated Raman activities. Nevertheless, DFT calculations are very useful for assignment of the observed Raman features based on their measured vibrational frequencies [15,80].…”

“…By comparing the Raman spectra calculated for configurations A, B and C one can understand of how the molecular configuration fluctuations, or in our case the protein conformational changes, may impact the Raman peak intensities and give rise to Raman blinking in experimental situations. However, it is important to underline that the interpretation of the SERS blinking phenomenon is still under debate in the SERS community and vibrational frequency fluctuations were reported and exploited in very few works [80]. The main issue lies in the modeling of realistic situations (interaction of large molecules physically or chemically adsorbed on a surface) at the atomic scale using quantum chemistry techniques.…”

Conjugates of Gold Nanoparticles and Antitumor Gold(III) Complexes as a Tool for Their AFM and SERS Detection in Biological Tissue

“…Moreover, we assume that the vibrations with strongly enhanced intensities in the range below 500 cm −1 are carrying the information on the complex-NPs interaction. These shifts belong [63].…”

High stability of ultra-small and isolated gold nanoparticles in metal–organic framework materials

“…This finding is supported by Raman spectra (Figure 5b) of Au/MOF-808-SH where the Au-S stretch vibration (calculated at 254 cm -1 and measured at ~234 cm -1 ) is in close vicinity to the Au-O mode (calculated at 296 cm -1 and measured at ~259 cm -1 ) for the pmba/Au film system, 77 which is consistent with a larger width for the mode at ~ 259 cm -1 (Table S9) The calculations further suggest that the -OH and carboxylic chemical groups should be affected after Au NP nucleation in specific ways (SI Section C-7). We have therefore performed IR absorption and Raman scattering 78 experiments to characterize the interaction between Au NP surfaces and ligands btc and pmba after synthesis in both MOF-808 ( Figure 4) and MOF-808-SH ( Figure 5). As predicted, the narrow bands at 3675 cm -1 (Figure 4a) and 3671 cm -1 (Figure 5a) for MOF-808 and MOF-808-SH, respectively, assigned to the stretch of the four bridge O-H groups in the SBU nodes (Figure 2a, e), 79 disappear after synthesis, consistent with direct bonding of Au to O (SI Section C-8.1).…”