Nanotechnology has been the subject of significant scientific and biomedical development efforts over the past decades. Improvement in biomarker discovery, targeting approaches and conjugation chemistries has led to the development of many novel nanomaterials for individualized therapy. In this thesis, we investigate a new class of nanomaterial called “nanofiber precursor” (NFP). The NFP is composed of multiple self-assembling peptides via electrostatic and non-covalent interactions. Each peptide consisted of β-sheet sequence attached to a methoxypolyethylene glycol (mPEG) via a linker. By conjugating either near infrared fluorophore or therapeutic antibodies, we demonstrate the application of NFP in diagnosis and therapy of cancer respectively. The main objectives of this thesis are: (1) To design and synthesize a near infrared nanofiber for imaging urokinase plasminogen activator (uPA) activity (2) To develop a Herceptin-conjugated nanofiber as multivalent targeted system for increasing therapeutic efficacy of Herceptin, a monoclonal antibody used for breast cancer treatment. We were successful in conjugating near infrared dye NIR664 to the nanofiber as well as Herceptin on the surface of nanofiber. (1) The NIR-NFP conjugate could detect recombinant uPA activity with sensitivity of 3 ng. (2) The Herceptin-conjugated nanofiber (HER-NFP) was more than two fold effective in inhibiting growth of HER-2 positive cells. In the second half of the thesis, we have also investigated tumorigenic role of 15-LOX-1, a lipid peroxidizing enzyme in prostate cancer. The aim of this study was: (3) To investigate the role of 15-lipoxygenase-1 (15-LOX-1) in upregulation of uPA in PC-3 prostate cancer cells. As a whole, the research presented in this thesis is aimed at designing new strategies and understanding molecular mechanisms that lead to prevention and treatment of cancer.