A Femtomolar Detection Range via Plasmonic Biosensors Based on V-Shaped Optical Adhesives Waveguides

A versatile and low-cost plasmonic biosensor was designed, realized, and tested by combining a bioreceptor layer with a probe based on two plastic optical fibers (POFs) built-in with a sensing chip carried out via a multilayer on UV-curable optical adhesives. The proposed sensitive multilayer has been developed to excite the surface plasmon resonance (SPR) phenomenon on a gold surface in contact with the monitored bioreceptor layer. More specifically, a binding interaction between a bioreceptor layer and its analyte has been studied for the first time by exploiting SPR platforms based on UV-curable optical adhesives. First, a resin block with a V-shaped channel on its surface was designed and printed using a 3-D printer to locate the source and receiver on the same side. Then, the channel was covered by a silver layer to obtain the mirror effect. After this, it was filled with an UV-curable optical adhesive, with two POFs fixed at the end of the trench, in order to obtain the core of the sensor's waveguide. Finally, an optical buffer layer and a gold nanofilm were deposited on the core to excite the SPR phenomenon efficiently. The obtained SPR probe was first tested as a refractometer to obtain the bulk sensitivity, and then, following a functionalization process, binding tests were carried out to detect immunoglobulin (IgG) in the buffer. The experimental results show an ultralow detection limit of 1.17 fM, a detection range from 1 to 250 fM, and a sensitivity at low concentrations of 3.42 nm/fM.