Imaging nanomaterials in vitro and in vivo by exploring their intrinsic nonlinear optical signals
Abstract
The extension of nanotechnology to biomedical system creates a new and fast developing field, nanomedicine. A wide range of nanoparticles has been developed as imaging agents or drug carriers. However, the translation of nanomedicines to a clinical setting has been slowed down due to a limited fundamental understanding of the nano-bio interaction. My thesis work describes the efforts in imaging the behavior of nanomaterials in live cells and animals by exploring the nonlinear optical properties. The first part of my thesis focuses on study of metallic and semiconducting nanoparticles in biological environment using their nonlinear optical signals. In chapter 2, systemic circulation of PEGylated gold nanorods (GNRs) is visualized by intravital two-photon luminescence (TPL) imaging. A biphasic clearance is demonstrated with branched PEG showing longer circulation. Following clearance, cellular biodistribution of GNRs in organs is mapped by TPL imaging. GNRs accumulate in macrophages in liver and spleen (Langmuir, 2009, 25, 12454-12459). In chapter 3, a bright three-photon luminescence is discovered from Au-Ag alloyed nanostructure by excitation with a femtosecond laser at 1290 nm, which enables bio-imaging with negligible photothermal toxicity and tissue autofluorescence (Angew Chemie, 2010, 49, 3485-3488, inside cover story). In chapter 4, a new contrast is invented for label-free, real-time imaging of single-walled carbon nanotubes (SWNTs) by pump-probe microscopy. At pump/probe wavelength of 707 and 885 nm, semiconducting and metallic SWNTs (S-SWNTs and M-SWNTs) exhibit intense stimulated emission and absorption signals, which allow us to monitor the intracellular trafficking, distribution in tissues, and systemic circulation in vivo with single-nanotube sensitivity and sub-micron resolution. The second part presents label-free imaging of nanomedicines in live cells by coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy. First, receptor-medicated endocytosis is visualized with a polymeric nanoparticle-based CARS probe (J. Phys. Chem. B, 2007, 111, 9980-9985). Second, the cellular drug delivery mechanism by poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) is reexamined by CARS microscopy and new discoveries that PLGA NPs are not readily taken up by cells and delivered the payload to cells by extracellular drug release and/or direct drug transfer to contacting cells are found (Mol. Pharmaceutics, 2009, 6, 190-201). Third, the sensitivity of SRS microscopy is improved to monitor liposomal drug delivery in live cells. The last part of my thesis depicts the applications of GNRs in diagnosis and phtotothermal therapy of tumor cells and activated macrophages. Photothermal effect of GNRs is monitored by TPL, confocal microscopy and biological assays. The formation of membrane blebs is observed. The subcellular mechanism is investigated to be a downstream effect of compromised membrane integrity, which permits influx of calcium and subsequent disruption of the actin network (Adv. Mater. 2007, 109, 3136-3141, cover story). In addition, cell death through necrosis or apoptosis is induced by controlling laser irradiation. The molecular mechanisms are determined as the loss of plasma membrane integrity for necrosis and intracellular perturbation with damage of mitochondria for apoptosis (Nanomedicine, 2009, 4, 265-276).
Degree
Ph.D.
Advisors
Cheng, Purdue University.
Subject Area
Analytical chemistry|Biomedical engineering|Nanotechnology
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