Imaging chromophores with undetectable fluorescence by stimulated emission microscopy

Super-resolution microscopy For imaging beyond the diffraction limit, to resolve tiny features in cells for example, researchers have so far had to rely on tagging the imaged object with fluorescent chromophores or on other microscopy techniques that do not exploit fluorescence but are much less sensitive. A team from the Department of Chemistry and Chemical Biology at Harvard has now developed an alternative approach known as stimulated emission microscopy, incorporating experimental techniques previously used in other multiphoton microscopies. The sensitivity of the method was demonstrated in applications including label-free microvascular imaging and monitoring lacZ gene expression with a chromogenic reporter. The technique is orders of magnitude more sensitive than absorption, is not subject to interference from other chromophores in the sample, and is amenable to three-dimensional sectioning. Importantly, all molecules are potential targets for stimulated emission microscopy, so it can be used to image non-fluorescing substances such as haemoglobin previously inaccessible to super-resolution microscopy.