Nanoplasmonics and surface enhanced spectroscopy 

Plasmonic nanocavity metasurfaces based on femtosecond laser-nanostructured patterns perspective for the enhanced optical response of organic and biological molecules
Berezovska N.1, Dmitruk I.1, Yeshchenko O.1, Kudrya V.1, Stanovyi O.1, Tomchuk A.1, Hrabovskyi Ye.1, Golovynskyi S.2, Xue B.2, Qu J.2, Dmytruk A.3
1 Faculty of Physics, Taras Shevchenko National University of Kyiv.  Volodymyrska Street, 64/13, Kyiv-01601, Ukraine. 
E-mail: n_berezovska@univ.kiev.ua
2 College of Physics and Optoelectronic Engineering, Shenzhen University. 518060 Shenzhen, P. R. China.
2 Department of Photon Processes, Institute of Physics of NAS of Ukraine. Prospect Nauky, 46, Kyiv-03028, Ukraine.

Plasmonic nanocavity metasurfaces based on femtosecond laser-induced periodic surface structures (LIPSSs) with noble metal nanoparticles (NPs) in near-field proximity can provide excitation of plasmon gap mode and respective electromagnetic (EM) field enhancement that causes an increase of the spectroscopic signal by up to several orders of magnitude in surface enhanced Raman scattering (SERS) or surface-enhanced fluorescence (SEF). That has been demonstrated on adsorbed species of biomolecules of low concentration [1]. 
Within the scope of present report, we study an efficiency of the application of LIPSSs either directly fabricated on metallic surfaces or obtained on semiconductor substrates subsequently coated with metallic gold or silver films for highly sensitive fluorescent label-free detection and imaging of biomolecules (nucleotides) or dyes (Rhodamine 6G) at room temperature. We discuss the most relevant parameters for the generation of different LIPSSs, as well as an impact of shape and size of metal NPs placed in the vicinity of metal or metal-semiconductor substrate on the efficiency of formation of plasmonic “hot spots”, i.e. the spatial areas with highly intense EM field where the huge plasmon enhancement occurs.

1.	Yeshchenko O.A., Golovynskyi S., Kudrya V. Yu., et al. Laser-Induced Periodic Ag Surface Structure with Au Nanorods Plasmonic Nanocavity Metasurface for Strong Enhancement of Adenosine Nucleotide Label-Free Photoluminescence Imaging // ACS Omega.-2020 -5.-P. 14030-14039.