Chiral Plasmonic Superlattices Based for Biosensing

Surface plasmons are coherent and collective oscillations of conduction electrons along the surface of a metal. In plasmonic metal nanoparticles, these oscillations result in remarkable optical properties that can be finely tuned under appropriate conditions. Chiral plasmonic metal nanoparticles have recently demonstrated chiral electromagnetic field enhancement and strong interaction with chiral materials. In 2020, Liz-Marzán’s group demonstrated the synthesis of chiral Au nanorods using chiral micelles formed from dissymmetric cosurfactants.¹ The sharp chiral surface wrinkles led to dissymmetry <i>g</i>-factors on Au nanorods as high as ~0.20.<br/><br/>Besides using circular dichroism spectroscopy and surface-enhanced Raman spectroscopy (SERS) independently for biosensing, surface-enhanced Raman optical activity (SEROA), combining SERS with Raman optical activity (ROA), makes use of highly polarizable chiral platforms that can discriminate enantiomers via SERS using equal amounts of left-hand and right-hand circularly polarized light. Chiral plasmonic metal nanostructures have recently demonstrated chiral electromagnetic field enhancement and strong interaction with chiral materials, which is highly beneficial in SEROA. The plasmonic and chiroptical properties of individual chiral nanoparticles can be optimized with different overall shapes and sizes as well as the synthetic methods. But for practical sensing and enhanced-spectroscopy applications, it requires assemblies of plasmonic nanoparticles to large electromagnetic field at hotspots, enabling extremely high sensitivity, even down to single molecule detection under certain conditions. However, there are no (or very few) studies of understanding the effects of the interparticle/lattice spacing and orientation of chiral superlattices based on individual chiral nanoparticles on their chiroptical response.<br/><br/>In this work, we explore self-assembled chiral plasmonic superlattices to optimize their plasmonic properties and chiroptical responses for biosensing. By utilizing templated-assisted self- assembly,² we can construct hierarchical chiral plasmonic arrays demonstrating precise numbers of nanoparticles in each lattice. We anticipate self-assembled chiral nanostructures with exceptional chemical and optical properties will provide versatile designs for highly efficient and reproducible SEROA-based platforms for chiral molecule detection. A diverse range of substrates with varied patterns, nanoscale architecture, and hotspot chirality morphology can be produced using advanced nanofabrication techniques.³<br/><br/>References:<br/>1. G. González-Rubio, J. Mosquera, V. Kumar, A. Pedrazo-Tardajos, P. Llombart, D. M. Solís, I. Lobato, E. G. Noya, A. Guerrero-Martínez, J. M. Taboada, F. Obelleiro, L. G. MacDowell, S. Bals, L. M. Liz-Marzán, Micelle-directed chiral seeded growth on anisotropic gold nanocrystals. <i>Science </i><b>368</b>, 1472–1477 (2020).<br/>2. L. Scarabelli, D. Vila-Liarte, A. Mihi, L. M. Liz-Marzán, Templated colloidal self-assembly for lattice plasmon engineering.<i> Acc. Mater. Res.</i> <b>2</b>, 816–827 (2021).<br/>3. E. Er, T. H. Chow, L. M. Liz-Marzán, N. A. Kotov, Circular polarization-resolved Raman optical activity: a perspective on chiral spectroscopies of vibrational states. <i>ACS Nano</i> <b>18</b>, 12589–12597 (2024).