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J Biol Phys. 2007 Dec;33(5-6):433-43. doi: 10.1007/s10867-008-9084-1. Epub 2008 Jun 19.

Axial resolution enhancement by 4Pi confocal fluorescence microscopy with two-photon excitation.

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Institute of Biophysics, University of Ulm, 89069 Ulm, Germany.


Confocal fluorescence microscopy and two-photon microscopy have become important techniques for the three-dimensional imaging of intact cells. Their lateral resolution is about 200-300 nm for visible light, whereas their axial resolution is significantly worse. By superimposing the spherical wave fronts from two opposing objective lenses in a coherent fashion in 4Pi microscopy, the axial resolution is greatly improved to approximately 100 nm. In combination with specific tagging of proteins or other cellular structures, 4Pi microscopy enables a multitude of molecular interactions in cell biology to be studied. Here, we discuss the choice of appropriate fluorescent tags for dual-color 4Pi microscopy and present applications of this technique in cellular biophysics. We employ two-color fluorescence detection of actin and tubulin networks stained with fluorescent organic dyes; mitochondrial networks are imaged using the photoactivatable fluorescent protein EosFP. A further example concerns the interaction of nanoparticles with mammalian cells.

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