This project focuses on the recombinant production and characterization of highly pH sensitive oligopeptidyl nano constructs designed for the selective and efficient targeting toward the acidic microenvironment of tumor cells. Although the acidic tumor microenvironment (pH 6.5 – 7) is well-established (1), it has not been fully exploited in either diagnosis or therapeutic targeting mainly due to the difficulty of achieving (i) chemical activation in this weakly acidic range and (ii) a sufficient depth of tumor penetration. We are testing the feasibility of using our newly designed pH-sensitive nano constructs as a novel diagnostic tool in cancer therapy. We anticipate that the critical experiments will lead to the identification of an optimal nanoconstruct for tumor imaging and/or targeted delivery.