The long term goal of this proposal is the development of a commercial point-of-care device capable of electronically sensing single circulating tumor cells (CTC) in the peripheral blood of a cancer patient. The viratrode is a nanotechnology platform that represents a significant technological advance. It contains an electrode-based biosensor and can provide an inexpensive format for point-of-care diagnosis with high sensitivity. The viratrode incorporates a bioaffinity layer consisting of a ?kelp forest? of filamentous phage particles, in which each particle can display multiple ligands to a particular cancer cell surface marker. This format maximizes specificity and affinity, while minimizing biofouling. The viratrode incorporates a sensitive area detector capable of detecting single digit or lower nM concentrations of biomarkers. Our Technical Objectives focus on constructing viratrodes for detecting prostate cancer CTC?s. Our target markers include PSA, PSMA, PSCA, and vβ3 intergrins. The viratrodes will be optimized for the recognition and real-time electrical detection of prostate cancer cells that express the target markers in a biologically relevant fluid matrix.