Tunable Gold-on-SiO2 Nanopillar Arrays with Functionalized Nanoporous Layer for Enhanced Fluorescence Immunoassays

Porous metal plasmonic resonators demonstrate large on-chip resonance areas and expanded light-absorption bandwidth, which are favorable in sensitive plasmonic-based biosensors. However, the conventional fabrication methods can only provide porous metal resonators less degree-of-freedom in morphology, significantly limiting their optical properties. This work proposes a porous bimetallic nanopillar array biosensing platform, the nanoporous gold pillar (NPGP), enabled by a hybrid porosity-on-nanoarray nanofabrication method. NPGP achieves spectral tunability by setting the main resonance through the morphology of nanopillar-supported transition gold inner core while expanding the resonance spectra through the nanoporous gold outer crust. The capability of NPGP as an on-chip fluorescence sensing platform is demonstrated in the detection of soybean stay-green associated geminivirus (SoSGV). With trace amounts of virus in ground leaf buffer solutions, the porous metal morphology captures the virus with high efficacy. Combined with the high field-strength region of NPGP, a fluorescence enhancement two orders of magnitude higher than that of a gold plane is achieved. This work has provided a new hybrid nanofabrication method and nanoporous plasmonic architecture that can create highly tunable porous optical resonating devices for wide use in biological and chemical molecule detections.