Quantifying and Optimizing Photocurrent via Optical Modeling of Gold Nanostar-, Nanorod-, and Dimer-decorated MoS2 and MoTe2

Finite element simulations through COMSOL Multiphysics were used to optically model systems composed of Mo dichalcogenide lay- ers (MoTe2 and MoS2) and Au nanoparticles (spherical dimers, nanorods, and nanostars) to understand how their fundamental material properties as well as their interactions affect the photocurrent response. The absorption cross sections of the various Au nanoparticles linearly increase with respect to their increasing dimensions, hence being ideal tunable systems for the enhancement of the electric field in the dichalcogenide layers under visible and near infrared. The photocurrent through the MoTe2 and MoS2 substrates was enhanced by the addition of Au nanoparticles when the plasmonic response was localized in the area of the particle in contact with the substrate. Based on these findings, the use of Au nanoparticles can greatly improve the unique photocurrent properties of Mo dichalcogenides; how- ever, nanoparticle orientation and size must be considered to tune the enhancement at the specific wavelengths. This computational work provides useful design rules for the use of plasmonic nanomaterials in photocatalytic and photocurrent enhancement of transition metal dichalcogenides

Homology modeling and molecular dynamics simulations of MUC1-9/H-2Kb complex suggest novel binding interactions

International audienceHuman MUC1 is over-expressed in human adenocarcinomas and has been used as a target for immunotherapy studies. The 9-mer MUC1-9 peptide has been identified as one of the peptides which binds to murine MHC class I H-2K. The structure of MUC1-9 in complex with H-2K has been modeled and simulated with classical molecular dynamics, based on the x-ray structure of the SEV9 peptide/H-2K complex. Two independent trajectories with the solvated complex (10 ns in length) were produced. Approximately 12 hydrogen bonds were identified during both trajectories to contribute to peptide/MHC complex, as well as 1-2 water mediated hydrogen bonds. Stability of the complex was also confirmed by buried surface area analysis, although the corresponding values were about 20% lower than those of the original x-ray structure. Interestingly, a bulged conformation of the peptide's central region, partially characterized as a -turn, was found exposed form the binding groove. In addition, P1 and P9 residues remained bound in the A and F binding pockets, even though there was a suggestion that P9 was more flexible. The complex lacked numerous water mediated hydrogen bonds that were present in the reference peptide x-ray structure. Moreover, local displacements of residues Asp4, Thr5 and Pro9 resulted in loss of some key interactions with the MHC molecule. This might explain the reduced affinity of the MUC1-9 peptide, relatively to SEV9, for the MHC class I H-2K

Interface and Bulk Standing Waves Drive the Coupling of Plasmonic Nanostar Antennas

Finite element simulations of the optical behavior of gold nanostars in water reveal a new view of collective electron cloud oscillations, where localized surface plasmon resonances coexist with coherent delocalized interface waves, i.e., propagating surface plasmons. Gold nanostar spikes long enough to allow propagating polaritons and short enough to resonate with the spherical core serve as the substrate for the observed overlap between propagating modes and localized hot spots. Transverse plane plots reveal bulk polaritons coupled to surface ones. In light of these observations, we explore the mechanisms that drive plasmonic coupling in nanostars from the single spike level to multispiked and multiparticle systems

Shaping Gold Nanostar Electric Fields for Surface- Enhanced Raman Spectroscopy Enhancement via Silica Coating and Selective Etching

The application of gold nanostars in direct and indirect surface-enhanced raman spectroscopy (SERS) sensing has significantly grown in the past few years, mainly because of the particles’excellentfield enhancement properties. However,experimental demonstrations correlating SERS signal enhancements to specific morphology features of the nanostars are still scarce, primarily because of the complexity of the nanostar morphology itself. Herein, we have addressed this fundamental issueby synthesizing surfactant-free gold nanostars, coating them with a uniform silica layer, and then etching the silica away selectively with NaBH4to expose increasing amounts of the metallic surface. We have then functionalized the nanoparticles witha Raman active molecule, aminothiophenol (ATP), and compared the resulting SERS spectra with those obtained on surfactant-free stars functionalized with ATP. Through comparison of the experimental results with the electricfield intensities and distributions calculated viafinite element simulations, we have observed a strong correlation between the Raman signal enhancements obtained experimentally and the heat losses calculated on three-dimensional representations of the same nanostructures. We believe that our model could be used to predict the effectiveness of nanostars at enhancing SERS signalsbased on their overall morphology, even when thorough experimental characterization is lacking

Colloidal Plasmonic Nanostar Antennas with Wide Range Resonance Tunability

Gold nanostars display exceptional field enhancement properties and tunable resonant modes that can be leveraged to create effective imaging tags, phototherapeutic agents, and hot electron-based photocatalytic platforms. Despite having emerged as the cornerstone among plasmonic nanoparticles with respect to resonant strength and tunability, some well-known limitations have hampered their technological implementation. Herein we tackle these recognized intrinsic weaknesses, which stem from the complex, and thus computationally untreatable morphology and the limited sample monodispersity, by proposing a novel 6-spike nanostar, which we have computationally studied and synthetically realized, as the epitome of 3D plasmonic nanoantenna with wide range plasmonic tunability. Our concerted computational and experimental effort shows that these nanostars combine the unique advantages of nanostructures fabricated from the top-down and those synthesized from the bottom-up, showcasing a unique plasmonic response that remains largely unaltered on going from the single particle to the ensemble. Furthermore, they display multiple, well-separated, narrow resonances, the most intense of which extends in space much farther than that observed before for any plasmonic mode localized around a colloidal nanostructure. Importantly, the unique close correlation between morphology and plasmonic response leads the resonant modes of these particles to be tunable between 600 and 2000 nm, a unique feature that could find relevance in cutting edge technological applications