Optical adaptation of confocal microscopes for arbitrary imaging angles-and its application to sedimentation/creaming in dispersions

Confocal microscopy has become a powerful tool to obtain high-resolution, three-dimensional images after reconstruction of a point-by-point scan of the local fluorescence properties of a sample. For technical reasons, commercial confocal microscopes perform this scan in a manner that the x-y-plane of the scan is perpendicular to gravity and can be several square centimetres large (defined by the movement of displacement stages). The depth- or z-scan, on the other hand, is parallel to gravity and typically limited to 10-1000 micrometres depth. This is a constraint that limits the number of experimental scenarios in which confocal microscopy can be employed, since many experimental systems ask for images in which the main extension of the scan has an angle with gravity which is not 90 degrees. Using the example of different experimental systems (particle dispersions, emulsions, foams, foamed emulsions) that sediment or cream under gravity, we show here how the optical path of any confocal microscope can be inverted to obtain any imaging angle with respect to gravity without losing all pre-programmed scanning and reconstruction facilities.