Capillary flow experiments are described with fluorescent molecules, bacteria, and microspheres using fluorescence correlation spectroscopy as an analytical tool. The flow velocity in the microcapillary is determined by fitting autocorrelation traces with a model containing parameters related to diffusion and flow. The flow profile of pressure-driven flow inside a microcapillary is determined by using the fluorescence fluctuations of a small dye molecule. It was found that bacteria and microspheres are retarded in their flow by optical forces produced by the laser beam.

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An instrumental system is described for detecting and sorting single fluorescent particles such as microspheres, bacteria, viruses, or even smaller macromolecules in a flowing liquid. The system consists of microfluidic chips (biochips), computer controlled high voltage power supplies, and a fluorescence microscope with confocal optics. The confocal observation volume and detection electro-optics allow measurements of single flowing fluorescent particles. The output of the avalanche photodiode (single photon detector) is coupled to a real-time photon-burst detection device, which output can address the control of high voltage power supplies for sorting purposes. Liquid propulsion systems like electro-osmotic flow and plain electric fields to direct the particles through the observation volume have been tested and evaluated. The detection and real-time sorting of fluorescent microspheres are demonstrated. Applications of these biochips for screening of bacteriophages-type biolibraries are briefly discussed.

The selection of specific binding molecules like peptides and proteins from biolibraries using, for instance, phage display methods can be quite time-consuming. It is therefore desirable to develop a strategy that is much faster in selection and sorting of potential binders out of a biolibrary. In this contribution we separately discuss the current achievements in generation of biolibraries, single-molecule detection techniques and microfluidic devices. A high-throughput microfluidic platform is then proposed that combines the propulsion of liquid containing fluorescent components of the biolibrary through microchannels, single-molecule fluorescence photon burst detection and real-time sorting of positive hits.