Ultrafast laser printing of self-organized bimetallic nanotextures for multi-wavelength biosensing

Surface-enhanced spectroscopy (SES) techniques, including surface-enhanced photoluminescence (SEPL), Raman scattering (SERS) and infrared absorption (SEIRA), represent powerful biosensing modalities, allowing non-invasive label-free identification of various molecules and quantum emitters in the vicinity of nanotextured surfaces. Enhancement of multi-wavelength (vis-IR) excitation of analyte molecules of interest atop a single textured substrate could pave the way toward ultimate chemosensing performance and further widespread implementation of the SES-based approaches in various crucial areas, such as point-ofcare diagnostics. In this paper, an easy-to-implement ultrafast direct laser printing via partial spallation of thermally-thick silver films and subsequent large-scale magnetron deposition of nanometer-thick Au layers of variable thickness was implemented to produce bimetallic textured surfaces with the cascaded nanotopography. The produced bimetallic textures demonstrate the strong broadband plasmonic response over the entire visible spectral range. Such plasmonic performance was confirmed by convenient spectroscopy-free Red-Green-Blue (RGB) color analysis of the dark-field (DF) scattering images supported by numerical calculations of the electromagnetic (EM) near-fields, as well as comprehensive DF spectroscopic characterization. Bimetallic laser-printed nanotextures, which can be easily printed at ultrafast (square millimeters per second) rate, using galvanometric scanning, exhibited strong enhancement of the SEPL (up to 75-fold) and SERS (up to 106 times) yields for the organic dye molecules excited at various wavelengths. Additionally, comprehensive optical and sensing characterization of the laser-printed bimetallic surface structures allows substantiating the convenient spectroscopy-free RGB color analysis as a valuable tool for predictive assessment of the plasmonic properties of the various irregularly and quasi-periodically nanotextured surfaces.