Correlating Molecular Surface Coverage and Solution-Phase Nanoparticle Concentration to Surface-Enhanced Raman Scattering Intensities

Abstract

Control over the composition, shape, size, stability, and local dielectric environment of solution-phase metallic substrates is vital to consistent surface-enhanced Raman scattering (SERS) signals. Because of their inherent instability, solution-phase nanoparticles can undergo uncontrolled aggregation when target molecules are added. Here, we demonstrate that both molecular surface coverage of the Raman active molecule, 2-naphthalenethiol (2-NT), and nanoparticle concentration are critical parameters for obtaining reproducible SERS signals using solution-phase gold nanoparticles. Both gold nanoparticle and 2-naphthalenethiol concentrations are varied, and the extinction of the nanoparticle substrate and the SERS intensity of the target molecule are monitored as a function of time. These results indicate that extinction and SERS spectral intensities increase predictably below full monolayer surface coverage. When excess molecules are added, uncontrolled and irreproducible nanoparticle aggregation leads to optimal overlap between the plasmonic properties of the nanoparticles and the SERS excitation wavelength. Importantly, this is the first report which correlates solution-phase nanoparticle concentration and stability to molecular surface coverage for simultaneous localized surface plasmon resonance (LSPR) and SERS spectroscopic measurements. As a result, these data should facilitate the experimental design and use of solution-phase SERS substrates for more predictable molecular detection.

Spectral characterization and intracellular detection of Surface‐Enhanced Raman Scattering (SERS)‐encoded plasmonic gold nanostars

“…When being excited under 785 nm excitation, which is in resonance with the branch plasmon, the EF was almost tenfold greater at 10 nM than at 1 μM. It is likely that the non‐linear presentation could be attributed to multiple factors, such as anisotropic EM field distribution and inhomogeneous molecular coverage/polarity on the hot spots . However, the exact mechanism explaining these observations is beyond the scope of this paper and would be a topic of future comparative studies.…”

Biological and environmental media control oxide nanoparticle surface composition: the roles of biological components (proteins and amino acids), inorganic oxyanions and humic acid

“…25 In terms of toxicity studies this can interfere and/or mask any effects due to nanoparticles themselves and in terms of applications can cause uncontrolled functionality at the surface. [53][54][55] Nanoparticle aggregation can vary between different biological media as a result of their surface functionality, pH and ionic strength. 16 Many techniques including, but not limited to, ATR-FTIR spectroscopy, mass spectrometry, and surface enhance Raman spectroscopy are capable of providing information on the composition of the surface adsorbed layers.…”

Surface Enhanced Raman Spectroscopy Enables Observations of Previously Undetectable Secondary Organic Aerosol Components at the Individual Particle Level

“…SERS offers strong enhancements in Raman signal (up to 10 10 ) due to localized surface plasmon resonances (LSPRs) that activate over small spatial regions (< 10 nm). [19][20][21][22] SERS offers great promise to detect key functional groups in complex mixtures. Examples of compounds present in SOA with functional groups that SERS can probe include epoxides, organosulfates, and organonitrates.…”