Plasmonic assisted super-resolution axial distance sensitivity in fluorescence cell imaging

There is currently a great need to develop live-cell compatible optical microscopy tools that can provide super-resolution information on biomolecules, in particular for the study of membrane receptors. We present a novel imaging technique, which employs a nanoplasmonic substrate in combination with conventional confocal fluorescence lifetime microscopy, to deliver an axial position sensitivity of order 10 nm in whole cell imaging. The technique exploits the Purcell effect experienced by fluorescent molecules in the vicinity of noble metal nanoparticles, leading to a reduction of the radiative lifetime and a commensurate increase in fluorescence intensity. We employ this technique to map the topography of the cellular membrane, by imaging the fluorescent protein eGFP labeled to the receptor CXCR4, and further investigate receptor-mediated endocytosis in carcinoma cells. These results demonstrate a new approach in biological cell imaging, using bespoke plasmonic nanostructures to provide axial super-resolution sensitivity, while retaining compatibility with conventional fluorescence microscopy techniques.