Signal-To-Background Ratio Improvement For Single-Molecule Spectroscopy Using Tube Lens To Reduce The Effective Detection Region

We demonstrate the improvement in the signal-to-background ratio of squaraine-derived rotaxane dye molecules embedded in poly(methyl methacrylate) polymer film by reducing the area of the effective detection region in a confocal optical microscope system. It is found that a long-focal-length tube lens combined with the use of a pinhole can evidently minimize the effective detection volume as well as the background photons, and that the signal-to-background ratio of single molecules is improved to 24 experimentally.