Photomodulation of fluorescent upconverting nanoparticle markers in live organisms by using molecular switches.

Although fluorescence microscopy continues to be the method of choice by biomedical researchers to reconstruct images of cells and tissues containing optical labels, [1] there still exist many limitations. The diffraction of light imposes the major drawback and reduces the spatial resolution achievable by conventional microscopes, which cannot distinguish between molecular or nanoscale probes residing in close proximity to each other. This limitation can be overcome by multiphoton approaches and the help of molecular switches that, by undergoing reversible photoreactions between two isomers with different absorption properties, can