(142c) Direct Patterning of Plasmonic Nanohelicoids Via Circularly Polarized Light

Chiral plasmonic surfaces, characterized by nanohelicoidal structures forming 'forests,' exhibit substantial optical rotation but typically involve complex and expensive multi-step nanofabrication processes, limiting compatibility with diverse substrates. Additionally, achieving large-scale photonic patterns on polymeric and flexible substrates remains a challenging task. In this study, we present a breakthrough in substrate-tolerant direct-write patterning, demonstrating the fabrication of silver nanohelicoids with locally variable optical activity using circularly polarized light (CPL). Centimeter-scale chiral plasmonic surfaces can be produced within minutes using inexpensive medium-power lasers. The growth of nanohelicoids is governed by the symmetry-broken site-selective deposition and self-assembly of silver nanoparticles (NPs). The ellipticity and wavelength of incident photons serve as parameters to dynamically control the handedness and size of the printed silver nanohelicoids, allowing on-the-fly modulation of nanohelicoid chirality during direct writing. This process offers straightforward pathways to create complex multifunctional metasurfaces with high polarization rotation and fine spatial resolution. Our computer-driven direct-write system extends its capabilities by printing local patterns with various optical activities over distances spanning four orders of magnitude. Importantly, direct-write printing by CPL involves no organic ligand materials, promising in chiroptical diagnostics by enhancing sensitivity to the dielectric environment and eliminating the charge transport dilemma of solution-processed nanomaterials. We conducted spectroscopic detection of chiral analytes based on the CD peak wavelength shift of the printed chiral silver pattern. CD spectra of the pattern exposed to pepsin gradually red-shift with increasing concentration, demonstrating a limit of detection below 100 pM. Enantiomer selectivity is also confirmed through different absolute wavelength shifts observed upon the absorption of L- and D-lysine.
Processing simplicity, high polarization rotation, and fine spatial resolution of the light-driven printing of stand-up helicoids provide a rapid pathway to chiral plasmonic surfaces, accelerating the development of chiral photonics for health and information technologies.