Innovative multi-resonant plasmonic cup-shaped biosensors for ultra-wide detection ranges and ultra-low detection limits. The case of interleukin-1β detection

In this work, an innovative multi-resonant plasmonic cup-shaped platform was designed, developed, and combined with a bioreceptor layer to address two key issues in biosensing: the ultra-low limit of detection (LOD) and the ultra-wide detection range. A cup-shaped optical waveguide was utilized to achieve surface plasmon resonance (SPR) phenomena, exploiting a single fabrication step and featuring an integrated measurement cell, which enables easy integration into rapid and cost-effective point-of-care tests (POCTs). Changing the optical path in the cup-shaped waveguide, its peculiar geometry allows different plasmonic resonances to be triggered and monitored. To this end, as a proof-of-concept, three experimental configurations were explored and tested by simply changing the altitude from which light is launched/collected to/from the plasmonic cup-shaped waveguide through plastic optical fibers (POFs). For all three experimental configurations, the plasmonic cup-shaped sensor was first optically characterized to determine its bulk sensitivity. Then, after a functionalization procedure of the gold nanofilm with a bioreceptor layer specific for interleukin-1β (IL-1β) detection, the plasmonic cup-shaped biosensor was characterized to obtain the binding performance parameters. More specifically, the multi-resonant plasmonic biosensor demonstrated selective detection of IL-1β, an ultra-low LOD (at femtomolar concentration), and an ultra-wide detection range (about five orders of magnitude) using the same functionalized sensing area monitored differently. The experimental results reveal the potential of the SPR cup-shaped biosensor in terms of performance, versatility, and its ability to achieve a scalable and low-cost point-of-care device.