Currently the low-cost high-throughput technologies for the detection and diagnosis of cancer, predict the efficacy of therapy or assess the clinical outcomes are limited. In recognition of this challenge, the cancer Prevention Research Small Grant Program (PAR-08-055) of the NIH/NCI seeks to fund "pilot and feasibility studies" related to "identification, development, and evaluation of biological analytic techniques, methodologies, and clinical technologies relevant to pre-clinical cancer detection. In direct response to this PAR, in this application we propose to develop a novel low cost fiber optic biosensor tool (dip-probe) to measure the molecular biomarkers which can be utilized for early detection/diagnosis of cancer, monitor the therapy response or predict the clinical outcomes. This device will rely on combination tapered fiber optic biosensor (CTFOB) probe and diode laser excitation, and will function on a sandwich immunoassay principle. The amount of the analyte will be measured in the form of a florescence signal. The fluorescence signal will be generated by evanescent wave excitation. Additionally, several dip-probes can be used to measure multiple markers in a single sample. Furthermore, our preliminary findings suggest that this tool is capable of detecting small amounts of analytes in samples (10 times higher sensitivity) utilizing reduced amounts of reagents (10-100 folds less) and time (less than an hour) when compared to other currently available detection assay systems including Western blot, and bead-based Luminex immunoassay. Our proposed studies will have three specific aims. Specific aim # 1 will focus on enhancement of fluorescence signal by optimization of probe parameters (tapered angle, taper length and probe radius), and adoption of existing sandwich immunoassay techniques to fiber optic probes. In specific aim # 2 we will focus on increasing the detection speed and sensitivity by adopting catalyzed reporter deposition (CARD) method to fiber optic probes. The technique will be applied to detect and quantify multiple markers in a single sample (e.g. serum sample). Specific aim # 3 will be to optimize the cost, turnaround time and reagent usage of this technique and compare it with other detections techniques. Successful completion of these studies result in the development of a low cost, portable fiber optic tool which will be utilized in early detection, diagnosis, therapy efficacy, prognosis, and surveillance of several human malignancies.