This book explains and demonstrates an advancement of conventional Fluorescence Correlation Spectroscopy (FCS), namely Dual-Focus FCS (2fFCS). 2fFCS is a solution based, single-molecule measurement scheme which allows the precise determination ofdiffusion coefficients of fluorescently labeled molecules (such asproteins, DNA, or other particles) at sub-nanomolar concentrations.In contrast to conventional FCS, where inherent artifacts can leadto substantial errors in the measurement result, 2fFCS allows easy-to-reproduce and artifact-free measurements. This book gives an introduction to 2fFCS, explaining how 2fFCS is able to circumvent FCS inherent artifacts. Beneath the theoretical foundation of 2fFCS also applications will be shown. The reader should be familiar with the basics of fluorescence and microscopy techniques such as confocal microscopy. ukryj opis