Up-converting multi-modality super-resolution microscopy
- Publication Type:
- Thesis
- Issue Date:
- 2020
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Optical fluorescence microscopy is one of the most powerful tools known in the life sciences due to its ability to image living systems with temporal evolution. For the past four decades, microscopy technology has been developing in major ways, specifically, resolutions, penetration depth, imaging speed, and multi-dimensional imaging. The resolution of optical microscopy has been greatly limited by the diffraction limit of light, which in turn prevents optical microscopy from studying sub-cellular biological structures. Until the last century, the concept of super-resolution microscopy has been conceived and rapidly developed to overcome the diffraction limit. Although super-resolution technology has been used for more than three decades, there remain major challenges requiring further developments. For instance, high-resolution imaging often comes at the price of acquisition speed, which limits the imaging of moving molecules inside living cells. Deep-penetration depth with high-resolution imaging has been regularly affected by light scattering and absorption in opaque bio-samples, which restricts the imaging through deep biological tissue with high-resolution. The complexity of the biological system and the tiny size of the subcellular structure require multimodality imaging to be implemented, limited by the probes used in confined imaging. The goals of this Ph.D. are to explain: (1) high resolution, (2) deep penetration depth (3) fast speed, and (4) multiple modalities. This research tackles these challenges by using a new type of fluorescence probe – upconversion nanoparticles (UCNPs).
UCNPs represent an entirely new class of multiphoton probes that rely on high densities of multiphoton emitters in small particles. Each particle contains thousands of codoped lanthanide ions that form a network of photon sensitizers and activators, which upconverts near-infrared photons into visible light. Unlike other multiphoton processes, UCNPs have a large number of intermediate excited states which can absorb low energy photons which are then converted into high energy photons. Upconversion nanoparticles are highly controllable during the synthesizing process, e.g. sizes ranging from a few nanometers to 100 nanometers. Due to the advantages of narrow emission spectra, high chemical stability, low toxicity, long luminescence lifetime， and high resistance to photo-quenching and photobleaching of UCNPs and the large anti-Stokes spectral separation between excitation and emission, UCNPs have served as probes for background-free and photostable bioimaging. Taking advantage of the nonlinear photoresponse of rare earth elements inside UCNPs, a series of new modes of super-resolution technologies was developed in my thesis.
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