Combining Quantum Dot Nanoparticles with Expansion Microscopy Enables Three-Dimensional Wide-Field Super-Resolved Imaging

Biological tissue is inherently a three-dimensional structure. Therefore, detailed biological investigations require three-dimensional imaging of cells and tissue microstructures. Given the limitations in traditional light microscopy and a lack of photostable labeling, multiplexed imaging of biological molecules with high precision is difficult to achieve. While recent advances in super-resolution microscopy (SRM) address some of the limitations associated with conventional optical imaging, they impose severe limitations on acquisition speed and are technically challenging. Expansion microscopy (ExM) is a recent development in SRM that enables nanoscale imaging on conventional microscopes. ExM is a relatively simple tissue processing technique that relies on embedding a tissue specimen within a swellable polyelectrolyte hydrogel. When the hydrogel expands, the corresponding molecular labels smoothly expand within a diffraction-limited region, significantly improving spatial resolution. While increasing the tissue volume by 4x-20x dramatically improves resolution, confocal imaging becomes impractical for large samples. This is because label de-crowding dilutes fluorescence signal and prolonged exposure results in photobleaching of adjacent fluorophores. This dissertation focuses on overcoming these limitations by developing a fast tissue imaging methodology capable of multiplex three-dimensional imaging at super-resolution. This method combines widefield imaging with quantum dot nanoparticles (Qdots) in ExM labeling and deconvolution for contrast enhancement. Three major contributions leveraging the advancement of ExM in fluorescence imaging are discussed to this end. ExM compatible Qdot labeling for improved photostability, widefield imaging for improved signal-to-noise ratio with fast imaging speed, and deconvolution for further contrast, resolution improvement in three-dimensional volume rendering. The whole research opens the door to fast and relatively simple 3D nanoscale imaging for applications in biology and medicine at low-cost settings.