Super-Oscillatory Imaging of Nanoparticle Interactions with Neurons

Abstract

We are developing a super-resolution imaging technology, called the Nanoscope, to allow label-free imaging of sub-cellular processes in living neural cells at nanometre resolution. This technique is an enhancement to current confocal microscope technologies and, unlike most super-resolution technologies, does not rely on fluorescent labelling. The phenomenon of super-oscillation means that by precisely controlling the interference of many band-limited waves, it is possible to generate a local region containing very high spatial frequencies. In the context of optics, this allows us to break the diffraction limit by making arbitrarily small spots far from any lens, within a dark field-of-view, surrounded by sidebands - trading efficiency for resolution. We select scattered light from the central spot using conventional optics, eliminating the sidebands and achieving resolution determined by central spot size.Our approach replaces a conventional microscope objective with a ‘super-oscillatory lens’ which sculpts the input light to form our strongly-confined spot. We have two methods of achieving this: the first uses a carefully designed set of concentric metal rings milled on a glass substrate to focus the light directly. The second method uses a spatial light modulator to structure the beam incident on a standard objective, shaping the standard focal spot into a sub-wavelength super-oscillatory spot.We will use the super-oscillatory microscope to further the understanding of cellular function, during health and neurodegenerative diseases. Our initial experiments utilise unlabelled gold nanorods (500x75nm) in low-density primary neuronal cultures. Localisation and tracking of individual gold nanoparticles will allow us to determine the effect of nanoparticles on cell function, mechanisms of uptake and potential clearing. This technique can also be used to investigate the general mechanisms of uptake and subcellular trafficking, providing information on the cell's essential abilities to dynamically compartmentalise materials within the neuronal architecture.