Elucidating the Chemisorption Phenomena in SERS Studies via Computational Modeling

Abstract

Colloidal gold solutions with nanostars and nanospheres as well as Klarite™ gold and gold-copper bimetallic substrates were used for SERS analysis of aniline and nitroaniline isomers to investigate their chemisorption phenomena. Computational modeling based on Density Functional Theory (DFT) was used in conjunction with the SERS analysis to study the adsorption behaviors of the analytes on metal surfaces. Gold nanospheres and Klarite™ samples produced about a 10-fold increase in signal enhancement compared to gold nanostars for the SERS analysis of aniline, nitroaniline isomers, and nitrobenzene. Signal enhancement is significantly greater for aniline compared to nitrobenzene and it is dependent on the proximity of the NH 2 to the NO 2 group for the nitroaniline isomers. Charge-transfer in chemisorbed analytes is an important contributing factor for SERS signal. The relative strengths of enhancement can be predicted by the DFT calculation of the HOMO-LUMO energy gaps of the analyte-metal cluster. Aniline and the three nitroaniline isomers showed stronger preference for the copper substrates if both the gold and copper substrates are present. The NO 2 group in 2-nitroaniline has a very strong preference and affinity for the copper in the Au-Cu bimetallic cluster.

N-Doped Graphenelike Nanostructures fromp-Nitro Aniline-Based Foam: Formation, Structure, and Applications as a Nanofiller

“…The Raman spectra of the PNA-based foam and its derived nanostructures are presented in Figure , while the Raman spectrum of pure PNA is discussed elsewhere. , The Raman features of the present extracted nanomaterials (Figure a) are similar to those of graphene containing heteroatoms . In contrast, the spectrum of the PNA-based foam (Figure b) resembles that of amorphous carbon, which contains defects and side chains as proposed previously in the literature. − The extracted sample also presents D, G, and 2D Raman shifts, and they upshifted toward higher frequency (related to graphene), which distinguishes them from graphitic systems. − The D and G bands in our samples are owing to the presence of polyaromatic hydrocarbon lattices dominated by sp 2 sites, along with a few sp 3 sites because visible excitation only resonates with the π states. , Herein, the G band is due to the bond stretching of all pairs of sp 2 atoms in six-membered rings, while the D band is due to the breathing modes of sp 2 atoms in rings and sp 3 hybridized carbon atoms at edges. − The upshifts imply the presence of N atoms in the ring, which cause notable distortion in the crystal lattice, as elaborated by other researchers. , The intensity ratio of D and G bands offers a gauge for the number of essential defects and serves as a quantitative measure of the edge plane exposure.…”

“…The Raman spectra of the PNAbased foam and its derived nanostructures are presented in Figure 6, while the Raman spectrum of pure PNA is discussed elsewhere. 29,30 The Raman features of the present extracted nanomaterials (Figure 6a) are similar to those of graphene containing heteroatoms. 26 In contrast, the spectrum of the PNA-based foam (Figure 6b) resembles that of amorphous carbon, which contains defects and side chains as proposed previously in the literature.…”

Cu@Au self-assembled nanoparticles as SERS-active substrates for (bio)molecular sensing

“…Both metals have well-known plasmonic properties due to localized surface plasmon resonance (LSPR), which has significant importance in the development of SERS substrates. AuCu bimetallic NPs have been demonstrated to show enhanced LSPR depending on the Cu content that is associated with electromagnetic coupling effect [23][24][25]. On the other hand, the preparation of AuCu SERS substrates typically requires the use of templates and/or high temperatures, which make synthesis methods costly and, therefore, not suitable for scale up production.…”

Using Molecular Electrostatic Potentials and Frontier Orbitals for the Surface-Enhanced Raman Interpretation of Fluoxetine

“…There are numerous examples in the literature in which the target molecule is attached to a cluster of metal atoms and the changes in the computed Raman spectra are discussed. [10][11][12][13][14][15][16] The size of these clusters varies between a single atom and 20 atoms, [17][18][19] with an alternative approach (periodic boundary conditions) getting some attention. 20 Common to many studies is the use of B3LYP as a standard functional and relatively small double-zeta basis sets.…”