Enhancing detection sensitivity and molecular binding rate in plasmonic nanostructures

• Main Authors: Lin, En-Hung, 林恩宏
• Other Authors: Lee, Ming-Chang
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/67975209787347614062

博士 === 國立清華大學 === 光電工程研究所 === 103 === In this dissertation, we report new methods to efficiently improve the detection limit of surface plasmon resonance in periodic metallic nanostructures by using small angle illumination, spectral integration analysis and dispersion curve of structure. We also present the dynamic study of optical trapping of fluorescent molecules using high-density gold nanodisk arrays. In nanoslit structure, the large-area gold nanoslit arrays were fabricated by thermal-annealing template-stripping method. The slit width and period was 60nm and 500 nm. The small angle illumination induced a resonant coupling between surface plasmon mode and substrate mode. It increased ~2.24 times intensity sensitivity at 5.5° incident angle. The small-angle illumination also resulted in multiple resonant peaks. The spectral integration method integrated all changes near the resonant peaks and increased the signal to noise ratio about 5 times as compared to single-wavelength intensity analysis. In nanohole structure, the large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method. The hole diameter and period was 180nm and 600nm. The (±1,∓1) surface mode which has higher angular RIU sensitivity of surface plasmon resonance improvement ~440 deg/RIU by change angle of light incident. The flat dispersion curve of (±1,∓1) surface mode was observed by large angle illumination due to electric field localized in hole cavity. It increased ~6.2 times than (±1,0) surface mode near 0° and also increased ~2.3 and ~4.5 times than prism coupler-based SPR sensor of angular RIU sensitivity at 630nm and 850nm, respectively. In gold nanodisk strucutre, the gold nanodisks were fabricated by electron beam lithography with a diameter of 500 nm and a period of 1 μm. Dark-field illumination showed ∼15 times enhancement of fluorescence near edges of nanodisks. Such enhanced near-field generated an optical trapping force of ∼10 fN under 3.58 × 103 W/m2 illumination intensity as calculated from the Brownian motions of 590 nm polystyrene beads. Kinetic observation of thiolated DNA modified with Cy5 dye showed different binding rates of DNA under different illumination intensity. The binding rate increased from 2.14 × 103 s−1 (I = 0.7 × 103 W/m2) to 1.15 × 105 s−1 (I = 3.58 × 103 W/m2). Based on above methods, it efficiently improves the intensity and angular sensitivity of surface plasmon resonance such as small angle incidence, spectral integration and dispersion curve of strucutre. Furthermore, gold nanodisks also efficiently improve both detection limit and interaction time.