Disclosed herein are programmable, conditionally activated small interfering RNA constructs (Cond-siRNAs) and methods of making and using the same as therapeutic agents. The Cond-siRNA comprises a sensor strand, a core strand, and a guide strand, which crossover to form a sensor duplex and a RNAi duplex attached to each other to form a single structure. Upon binding an input strand to the sensor strand, the Cond-siRNA is activated and releases RNAi targeting a desired gene.