|Wednesday, March 24|
Nanophotonic Approaches for Chirality Sensing
* Christy F. Landes, Rice University, United States
Stephan Link, Rice University, United States
Chiral nanophotonic materials are promising candidates for biosensing applications because they focus light into nanometer dimensions, increasing their sensitivity to the molecular signatures of their surroundings. Recent advances in nanomaterial-enhanced chirality sensing provide detection limits as low as attomolar concentrations (10-18 M) for biomolecules and are relevant to the pharmaceutical industry, forensic drug testing, and medical applications that require high sensitivity. Chiral nanomaterials have potential applications in detecting biomolecules, supramolecular structures, and other environmental stimuli. I will discuss the plasmon-coupled circular dichroism mechanism observed in plasmonic nanoparticles and discuss how hotspot-enhanced plasmon-coupled circular dichroism applies to biosensing. I then will discuss single-particle spectroscopic methods for achieving the ultimate goal of single-molecule chirality sensing. Finally, I will propose future directions for nanophotonic chiral systems.
Molecular-Scale Ligand Effects in Small Gold-Thiolate Nanoclusters
* Daniel Chevrier, Bioscience and Biotechnology Institute of Aix-Marseille, CEA Cadarache, France
Because of the small size and large surface area of thiolate-protected Au nanoclusters (NCs), the protecting ligands are expected to play a substantial role in modulating the structure and properties. However, little is known on how thiolate ligands explicitly modulate the structural properties of the NCs at atomic level, even though this information is critical for predicting the performance of Au NCs in application settings (e.g., catalyst interacting with small molecules, sensor interacting with biomolecular systems). This talk will review a recent combined experimental and theoretical study using synchrotron X-ray spectroscopy and quantum mechanics/molecular mechanics simulations that investigates how the protecting ligands impact the structure and properties of small Au18(SR)14 NCs (SR - thiolate ligand). Two representative ligand types smaller aliphatic cyclohexanethiolate and larger hydrophilic glutathione are selected and their structures are followed experimentally in both solid and solution phases. It was found that cyclohexanethiolate ligands are significantly perturbed by toluene solvent molecules, resulting in structural changes that cause disorder on the surface of Au18(SR)14 NCs. In particular, large surface cavities in the ligand shell are created by interactions between toluene and cyclohexanethiolate. In contrast, glutathione ligands encapsulate the Au NC core via intermolecular interactions, minimizing structural changes caused by interactions with water molecules. The protection from glutathione ligands imparts a rigidified surface and ligand structure, making the NCs desirable for biomedical applications due to the high stability and offering a structural-based explanation for the enhanced photoluminescence often reported for glutathione-protected Au NCs.