SERS enhancement of gold nanospheres of defined size

Abstract

Monodisperse, citrate-stabilized gold nanoparticles of sizes ranging from 15 to 40 nm were synthesized and characterized by small angle X-ray scattering and UV-vis experiments. Identical surface properties of nanoparticles of different sizes to avoid variation in the chemical surface-enhanced Raman scattering (SERS) enhancement, as well as selection of experimental conditions so that no aggregation took place, enabled the investigation of enhancement of individual nanospheres. Enhancement factors (EFs) for SERS were determined using the dye crystal violet (CV). EFs for individual gold nanospheres ranged from 10 2 to 10 3 , in agreement with theoretical predictions. An increase of the EFs of individual spheres with size can be correlated to changes in the extinction spectra of nanoparticle solutions. This confirms that the increase in enhancement with increasing size results from an increase in electromagnetic enhancement. Beyond this dependence of EFs of isolated gold spheres on their size, EFs were shown to vary with analyte concentration as a result of analyte-induced aggregation. This has implications for the application of nanoparticle solutions as SERS substrates in quantitative analytical tasks.

SERS in Cells: from Concepts to Practical Applications

“…These changes in SERS enhancement indicate morphological differences of the gold nanostructures inside the endosomal vesicle, that were explained by the formation of nanoparticle aggregates [2]. Recently, in accordance with theoretical predictions, we have shown experimentally that the enhancement of individual gold nanospheres is very low, around 10 2 , but that the formation of aggregates can change the enhancement factor by many orders of magnitude [54].…”

“…Therefore, the spectral information that can be obtained for the biological component is coupled very strongly to the physicochemical properties of the nanoparticles. In a SERS experiment, this strong connection expresses in the following characteristics: (i) The observed SERS intensities vary with the enhancement factor, which depends critically on the ability of the nanoparticles to form aggregates [54,55]; (ii) the enhancement depends on the type of aggregates, particularly on the size of the gap between nanoparticles and their geometries [56][57][58][59]; and (iii) the average intensity will depend on the number of nanoparticles or nanoaggregates in the probed volume. As we will discuss in the next section, the plasmonic properties of noble metal nanoparticles can be greatly altered in the course of the interaction of the nanoparticles with the cell.…”

Shape-dependent antibacterial effects of non-cytotoxic gold nanoparticles

“…However, the position of the peak is markedly red shifted by ~34 nm compared to AuNSs of the same diameter. 51 This can be explained in the context of plasmon hybridization theory, 52 which regards the AuNFs as a hybrid of spheres and branched or rod-shaped particles. 50,53 This results in a plasmon resonance peak position intermediate to that of spheres (~530 nm) and branched (~700 nm) particles.…”

Characterization and Visualization of Vesicles in the Endo-Lysosomal Pathway with Surface-Enhanced Raman Spectroscopy and Chemometrics

“…10,11 Reporter-free SERS, especially involving spatially resolved maps, however, can generate large and complex data sets which require more sophisticated analysis methods to extract significant features. 3 An accompanying complication especially with the reporter-free SERS methodology in cells is that the variation in the state of aggregation can result in a large variation of the intensity and the spatial distribution of the measured spectra 12,13 making single or average spectra insufficient for complete sample characterization (or classification).…”