Disclosed herein are novel synthetic polypeptides and uses thereof in the preparation of liposomes. According to embodiments of the present disclosure, the synthetic polypeptide comprises a membrane lytic motif, a masking motif, and a linker configured to link the membrane lytic motif and the masking motif. The linker is cleavable by a stimulus, such as, light, protease, or phosphatase. Once being coupled to a liposome, the exposure to the stimulus cleaves the linker that results in the separation of the masking motif from the membrane lytic motif, which in turn exerts membrane lytic activity on the liposome that leads to the collapse of the intact structure of the liposome, and releases the agent encapsulated in the liposome to the target site. Also disclosed herein are methods of diagnosing or treating a disease in a subject by use of the present liposomes.