Multiwavelength plasmonic activity in aluminum-based 2D nanostructures for biosensing applications

Surface plasmons (SP) can be effectively tuned in the entire UV-visible-near-infrared (NIR) spectrum, bringing together a variety of optical sensors to monitor the surrounding conditions at the metal-analyte interface. To initiate such a plasmonic phenomenon, aluminum (Al) as a plasmonic metal has gained much industry-related relevance, being relatively low-cost and widely available, and furthermore is compatible with CMOS technology. In the present work, we have employed Al-based 2D plasmonic nanostructures with different periodicity in the x and y directions, placed over a thin Al film, to observe transmission peaks at SP resonances. Modulating different geometric parameters including the height, width, and thickness of the Al film deposited below the nanostructures yielded an optimized design. As a result, when light is incident normally, the 2D periodic nanostructures produce a transmission peak corresponding to SP resonance for a period (P-X) = 1000 nm (along the x-direction) in the NIR region, while for P-Y = 500 nm (along the y-direction), a transmission peak is produced in the visible region. Structures with different periods in different directions, exhibiting multiple SP resonances, could find potential applications in optical sensors, wherein characteristics of analytes coated on the nanostructures at different wavelengths could be extracted in a single experiment. In short, the proposed engineered plasmonic nanostructures open a new door for biosensing applications in both the visible and NIR regions with the same plasmonic substrate.