Thomas Ruckstuhl

The efficiency of surface-plasmon coupled emission for sensitive fluorescence detection

Surface-plasmon coupled emission (SPCE) has emerged as a new and potentially powerful tool for highly sensitive fluorescence detection. In the case of SPCE, the fluorescence is collected through a semi-transparent thin metal film deposited on glass. We present a theoretical analysis of SPCE, studying the potential enhancement of the fluorescence collection efficiency, brightness, quantum-yield, and photostability. The results are compared with fluorescence detection on a pure glass surface. It is shown that SPCE does not lead to any improvement, but that the metal film actually reduces the sensitivity of fluorescence detection.

Measuring large numerical apertures by imaging the angular distribution of radiation of fluorescing molecules

Exact knowledge of the numerical aperture is crucial in many applications using high-aperture objectives such as confocal microscopy, optical trapping, or advanced sub-wavelength imaging methods. We propose and apply a precise and straightforward method for measuring this fundamental parameter of microscope objectives with numerical apertures above unity. Our method exploits the peculiarities of the fluorescence emission of molecules at a glass/air interface.

Comparison between a conventional epifluorescence microscope and a new highly efficient evanescent wave detector in single molecule spectroscopic applications

We present a comparison between two basically different optical detection systems: a confocal epifluorescence microscope, and a new evanescent wave detection system employing a parabolic optical element. In a microscope set-up, fluorescence light is collected within a cone around the optical axis, whereas in the evanescent light detector, fluorescence light is collected mainly at angles larger than the so-called critical angle of total internal reflection. Based on a thorough theoretical modeling of both experimental set-ups, comparison between the two detection systems is made Particularly, the optical detection efficiency is compared. 5