Enhancing the Surface Sensitivity of Metallic Nanostructures Using Oblique-Angle-Induced Fano Resonances.
Surface sensitivity is an important factor that determines the minimum amount of biomolecules detected by surface plasmon resonance (SPR) sensors. We propose the use of oblique-angle-induced Fano resonances caused by two-mode coupling or three-mode coupling between the localized SPR mode and long-range surface plasmon polariton modes to increase the surface sensitivities of silver capped nanoslits. The results indicate that the coupled resonance between the split SPR (-kSPR) and cavity modes (two-mode coupling) has a high wavelength sensitivity for small-angle incidence (2°) due to its short decay length. Additionally, three-mode coupling between the split SPR (-kSPR), substrate (+kSub) and cavity modes has a high intensity sensitivity for large-angle incidence due to its short decay length, large resonance slope and enhanced transmission intensity. Compared to the wavelength measurement, the intensity measurement has a lower detectable (surface) concentration below 1 ng/ml (0.14 pg/mm(2)) and is reduced by at least 3 orders of magnitude. In addition, based on the calibration curve and current system noise, a theoretical detection limit of 2.73 pg/ml (0.38 fg/mm(2)) can be achieved. Such a surface concentration is close to that of prism-based SPR with phase measurement (0.1-0.2 fg/mm(2) under a phase shift of 5 mdeg).
Research Center for Applied Sciences, Academia Sinica, 128, section 2, Academia Road, Nangkang, Taipei 11529, Taiwan.
Kuang-Li
KL
Lee
Department of Optoelectronics, National Taiwan Ocean University, Keelung 20224, Taiwan.
Chia-Chun
CC
Chang
Research Center for Applied Sciences, Academia Sinica, 128, section 2, Academia Road, Nangkang, Taipei 11529, Taiwan.
Meng-Lin
ML
You
Research Center for Applied Sciences, Academia Sinica, 128, section 2, Academia Road, Nangkang, Taipei 11529, Taiwan.|Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30013, Taiwan.
Ming-Yang
MY
Pan
Research Center for Applied Sciences, Academia Sinica, 128, section 2, Academia Road, Nangkang, Taipei 11529, Taiwan.|Department of Optoelectronics, National Taiwan Ocean University, Keelung 20224, Taiwan.|Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan.
Pei-Kuen
PK
Wei