Molecular probes are critically important for molecular recognition for a variety of targets and biomarkers and for biosensor development. In this talk, we will discuss the development of molecular probes for molecular imaging of cancer cells. Confocal microscopy and optical spectroscopy have been used for the development and application of the molecular probes. In order to generate effective molecular probes for cancer cell recognition, we have developed a cell based apatmer selection strategy for the selection of a group of aptamers for tumor cell imaging. In this strategy, a tumor cell is used as a target for the selection of a group of aptamers which can recognize tumor cell surface biomarkers. A negative cell line is used to reduce the number of aptamers selected. We have selected a group of highly specific apatmer probes using tumor cells against normal cells. These aptamers have different Kd values ranging from sub-µM to pM. These aptamers have been used for cancer cell proteomics studies, cancer biomarker discovery and cancer cell molecular imaging.