Cancer is the second leading cause of death, claiming ̃0.56 million lives in the U.S. every year following heart diseases (̃0.62 million). From 1991 to 2007, mortality associated with heart diseases decreased 39%; by contrast, the death rate of cancer only decreased by 17% in spite of intensive research and improved therapeutics. The stagnation of conventional medicine and the complexity of cancer demand new therapeutic strategies. As an emerging approach, the use of nanomaterials as cancer diagnostic and therapeutic agents has shown promising results due to their unique physical and chemical properties. To date, more than two dozen nanoparticle-based products have been approved for clinical use and they show advantages over conventional therapeutics. However, translation of many other nanomaterials has been impeded due to concerns over toxicity and biodegradability. This dissertation presents the development of biodegradable luminescent porous silicon nanomaterials and their potential applications for imaging and treatment of cancer. Chapter 3 presents a diagnostic application of LPSiNPs. Time-gated fluorescence imaging of tumors using LPSiNPs with long emission lifetime is developed. This technique can effectively eliminate interference from short-lived tissue autofluorescence and improve the detection sensitivity. Chapter 4-6 demonstrate the therapeutic applications of porous silicon nanomaterials. In Chapter 4, magnetically- guided delivery of anticancer drug to cancer cells in vitro is achieved using magnetic, luminescent porous Si microparticles. Chapter 5 demonstrates that porous silicon nanoparticles can be used as photosensitizer and generate cytotoxic singlet oxygen when irradiated by light. The phototoxicity of the nanoparticles against cancer cells is also studied. Finally, the use of LPSiNPs for immune activation is investigated in Chapter 6

Fluorescence imaging is one of the most versatile and widely used visualization methods in biomedical research. However, tissue autofluorescence is a major obstacle confounding interpretation of in vivo fluorescence images. The unusually long emission lifetime (5-13 μs) of photoluminescent porous silicon nanoparticles can allow the time-gated imaging of tissues in vivo, completely eliminating shorter-lived (<10 ns) emission signals from organic chromophores or tissue autofluorescence. Here using a conventional animal imaging system not optimized for such long-lived excited states, we demonstrate improvement of signal to background contrast ratio by >50-fold in vitro and by >20-fold in vivo when imaging porous silicon nanoparticles. Time-gated imaging of porous silicon nanoparticles accumulated in a human ovarian cancer xenograft following intravenous injection is demonstrated in a live mouse. The potential for multiplexing of images in the time domain by using separate porous silicon nanoparticles engineered with different excited state lifetimes is discussed.

Recent far-reaching advances in synthetic biology have yielded exciting tools for the creation of new materials. Conversely, advances in the fundamental understanding of soft-condensed matter, polymers and biomaterials offer new avenues to extend the reach of synthetic biology. The broad and exciting range of possible applications have substantial implications to address grand challenges in health, biotechnology and sustainability. Despite the potentially transformative impact that lies at the interface of synthetic biology and biomaterials, the two fields have, so far, progressed mostly separately. This Perspective provides a review of recent key advances in these two fields, and a roadmap for collaboration at the interface between the two communities. We highlight the near-term applications of this interface to the development of hierarchically structured biomaterials, from bioinspired building blocks to 'living' materials that sense and respond based on the reciprocal interactions between materials and embedded cells.