Optical biosensing platforms based on Ga-graphene plasmonic structures on Cu, quartz and SiO2/Si substrates

Ga nanoparticles (GaNPs) produced by thermal evaporation or epitaxial methods on graphene sheets present strong plasmonic effects that can couple to graphene phonons. In this work, GaNPs are deposited on graphene monolayers supported on Cu, quartz, and SiO2/Si substrates. The use of graphene increases the interparticle distance and improves the size uniformity. The enhancement of G and 2D graphene Raman lines is analyzed for the different substrates under excitation at 633 and 532nm. The plasmonic effects are investigated using spectroscopic ellipsometry, finding a strong resonant mode at energies between 1.7 and 2.0eV and an incidence angle of 55.6 degrees. Finally, the heterogeneous surfaces are functionalized for the preparation of optical biosensors exposing the surface to 3,3-dithiodipropionic acid di(N-succinimidyl ester) (DTSP). A significant energy shift of the ellipsometric signal on the Ga/graphene surfaces is observed in comparison to Ga/Si surfaces. Sketch of GaNPs atop graphene and biofunctionalizing agent (DTSP). Dip in the Psi ellipsometric function, and associated step in the Delta function, found around the GaNPs-graphene coupling resonance at an incident angle of 55.6 degrees.