Highly efficient optical detection of surface-generated fluorescence.

We present a theoretical study of a new highly efficient system for optical light collection, designed for ultrasensitive fluorescence detection of surface-bound molecules. The main core of the system is a paraboloid glass segment acting as a mirror for collecting the fluorescence. A special feature of the system is its ability to sample not only fluorescence that is emitted below the angle of total internal reflection (the critical angle) but also particularly the light above the critical angle. As shown, this is especially advantageous for collecting the fluorescence of surface-bound molecules. A comparison is made with conventional high-aperture microscope objectives. Furthermore, it is shown that the system allows not only for highly efficient light collection but also for confocal imaging of the detection region, which is of great importance for rejecting scattered light in potential applications such as the detection of only a few molecules.