Abstract
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.