DNA是生物遺傳的基本物質，細胞根據特定DNA序列產生特定蛋白質，執行細胞中的正常生理功能。現有之DNA序列檢測技術曠時費日、價格不斐，發展快速而且便宜的DNA序列檢測技術乃時勢所趨。近場光學生醫掃瞄器結合微奈米流道與近場光源，以奈微米流道迫使DNA分子拉伸通過狹縫，近場光源激發序列上之螢光分子，接收隨時變的螢光訊號便可以得知序列順序。近場光源的優點在於其解析能力突破繞射極限，約為100nm，但是DNA序列分子大小在nm~Ǻ等級，因此目前無法直接以近場光學生醫掃瞄器定序DNA序列。
本論文提出以單邊激發的機制提高掃描器解析度。利用時域有限差分法模擬光波在奈米結構當中的傳遞情形，發現斜向入射光波引發狹縫中的directional coupling現象，狹縫出口處光能量匯聚於一點，猶如點光源，藉此大幅提高解析能力。
到目前為止，本論文已對空氣-金屬、水-金屬介面完成模擬，理論最佳解析度約為10nm。除此之外，經由Aperture SNOM的量測結果，可以證實單邊激發的效應，但是顯微系統解析能力尚不足以驗證理論解析度。未來的工作著重於改善Apertureless SNOM解析度，期望證明模擬結果，並且建構近場光學生醫掃瞄系統，以DNA或螢光分子直接流過近場光源，這樣便可以得到隨時變的螢光訊號，推測系統的實際解析度。

DNA molecules are the fundamental genetic elements of all creatures. According to the DNA sequence, cells produce certain albumins which execute ordinary physiology functions. Today’s techniques for sequencing DNA molecules are very expensive and take a lot of time, and it is impossible to sequence every human’s DNA. Therefore, there are great demands for a cheap and fast sequence technique.
Near-field bio-scanner combines nano-micro fluidic channels and near-field light source. Nano-micro fluidic channels enforce DNA molecules to stretch and to flow over the near-field light source and the fluorescent molecules on the DNA sequence can be stimulated. As a result, we can acquire time dependent sequence signal by detecting the fluorescent signal in the far-field. The advantage of the near-field source lies in the ability to break the diffraction limit, and the resolution is about 100nm. Nonetheless, the size of a single DNA sequence is on the order of nm~Ǻ. So far, we can not measure single sequence signal by near-filed bio-scanner.
This thesis proposes a new generation near-field bio-scanner using single side emission to advance the resolution limit of the bio-scanner. The finite-difference time-domain (FDTD) algorithm is used to explore the propagation behavior of the light wave in the nano-structures. We find that the directional coupling mechanism is evoked by incident light with oblique incident angle, and the energy converge into a small area promoting the resolution limit of the bio-scanner as a point light source in the best simulation parameters. To evidence the simulation results, we have used Aperture SNOM and Apertureless SNOM to measure energy distribution at the exit of the nano-slit.
So far, we have already completed the simulation of the air-metal interface and water-metal interface structures, and the theoretical optimize resolution ability is about 10nm. Otherwise, we have proofed single side emission phenomenon by measurements of Aperture SNOM, but the resolution ability of our homemade Aperture SNOM is not good enough to testify the simulation results. On the other hand, measurements of Apertureless SNOM are degraded by the interference between background noise and direct or indirect evanescent wave at the tip end. Improving Apertureless SNOM to prove simulation results is one of the most important missions in the future. Constructing near-field bio-scanner system to obtain time-varying signal of DNA molecule or fluorescence beads would be a direct way to testify our results.

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