Optical imaging in live cells has provided a wealth of information regarding the various biological mechanisms, including using genetically coded green-fluorescent protein-conjugated organic dye molecules and, more recently, highly luminescent quantum dots as optical tags for the target biomolecules. Cells are inherently complex, grow constantly and have autofluorescence covering the entire visible spectrum ranging from green to red. At the single quantum-emitter level, it is often difficult to distinguish optical probes from fortuitous fluorophores inside living cells owing to complexity and constant evolvement. We have developed photoswitchable nanoparticles-optical nanoprobes that can be highlighted in either red or green during fluorescence imaging. Such optically addressable nanoprobes offer unambiguous detection of sites of biological interactions, and successfully implementing such optically switchable nanoprobes should greatly reduce the occurrence of false-positives in biomedical imaging and unambiguous detections.