Detection of a single molecule in a capillary by laser-induced fluorescence

he objective of this dissertation is to develop a novel laser excited spectrometric method to reliably detect a single molecule in a flowing stream which is confined in a capillary. The laser is tuned to the rubidium atomic absorption line at 780.023 nm and focused onto the uncoated part of the capillary. A heated rubidium metal vapor filter based on the resonance absorption of an atomic vapor absorbs the laser specular scatter while passing the molecular fluorescence. The fluorescence is then focused by a microscope objective into an optical fiber which is prealigned to the detector. Raman scatter is reduced by flowing the molecules in the small probe volume. Background fluorescence is virtually eliminated by working in the near-infrared. The excitation source is a Ti:sapphire laser with a linewidth narrower than the rubidium atomic absorption bandwidth. The detector is a single photon avalanche photodiode with high photon detection efficiency and low dark count rate.;The concept of single molecule detection is addressed in terms of limit of detection, limit of guarantee, intrinsic noise, extrinsic noise, as well as detection efficiency and measurement efficiency. The generalized Lorentzian approximation for Voigt line shape is used to simulate the absorption profile of the rubidium metal vapor filter at different temperatures. The absorbance of the rubidium metal vapor filter at 170;A photostability study of IR140 molecules dissolved in methanol is evaluated to optimize laser power and molecular transit time in the probe volume. The linear range of calibration curve is from 1.5...