[10p-N404-1~14] 4.1 Plasmonics and Nanophotonics

▼ [10p-N404-11] Sensitive Small Molecule Detection Using Coupling of Image Dipoles of Gold Nanoparticles and Fano Resonance of Periodic Gold Nanostructures

〇(D)CHIAWEN KUO^1,2, Sheng-Han Wang², Shu-Cheng Lo^2,3, Ya-Lun Ho¹, Jean-Jacques Delaunay¹, Pei-Kuen Wei² (1.School of Engineering, The Univ. of Tokyo, 2.Research Center of Applied Sciences, Academia Sinica, 3.Inst. of Applied Mechanics, National Taiwan Univ.)

Keywords:surface plasmonic resonance, image dipole coupling, biosensor

Compared to conventional surface plasmon resonance (SPR) biosensor using a prism coupler, the metallic nanostructure-based plasmonic sensor takes advantage of high-throughput and on-chip detections. However, there are still some shortcomings in this technique, such as difficulty in small-molecule detection. To overcome this problem, we took a strategy to combine coupling of image dipole of gold nanoparticles (AuNPs) and periodic gold-capped-nanoslits (GCNs) to enhance the signal of small molecules by using both theoretical simulations and experiments for verification. In this work, we showed that the periodic GCNs can be regarded as a mirror for image dipoles of AuNPs. The surface plasmon polarizations (SPPs) on GCNs interacted with the dimer mode and coupled out to the far-field by the grating coupling of periodic gold caps. The results show that the peak intensity is decreased by the increasing gaps of the dimer mode, and the maximum intensity change can be attained when SPR matches the dimer resonance. By using the intensity change as the signal, 50-nm AuNPs can be detected with a surface density of less than one particles/µm². We applied this dimer mode story to Brucella abortus DNA detection. From the experimental results, the detection limit of B. abortus DNA is 10 fM. The LOD achieves three orders magnitude lower level compared to the prism-based SPR. This method provides an efficient way for detecting low-concentration small molecules, such as DNA, miRNA and peptides.