Cancer remains one of the most prevalent diseases to date. Detection of circulating tumor cells (CTCs) in the vasculature has been identified as a promising method for determination of cancer risk, cancer prognosis, and determination of the effect of therapy. This proposal aims to establish the feasibility of a system for optical detection of CTCs that could be used in a point-of-care setting. Nanoparticles doped with near-infrared fluorophores and with high affinity to the cancer cells will be utilized for tagging CTCs in blood samples. The nanoparticles will provide high signal amplification for ultrasensitive detection. Phase I will focus on the evaluation of the diagnostic setup using body fluids spiked with CTCs. Phase II will develop a prototype and optimize the system for detection of patient samples. This project is expected to result in a small and rapid sensor that could be used at a physician's office or at small diagnostic laboratories, and which could become essential for the diagnosis and management of cancer patients.