The conventional selection method used in directed evolution is not applicable to biosensors due to the unidirectional selection and loss of variance over the process. Thus, in this project we developed an in-vivo bidirectional selection system to allow directed evolution for biosensors with minimum loss of variance. The bidirectional selection system consists of a selection marker and accompanying workflow. The system allows screening of two diametric properties without in-vitro steps and reduces the variance loss. This allows selection for less leaky and stronger expression biosensors over multiple cycles of directed evolution.