We propose a scheme of a sensitive biosensor based on optical bistability (OB) in a biological semiconductor quantum dot (SQD)-DNA coupled nanohybrid. By plotting bistability phase diagrams within the system's parameter space, we show that the bistable effect can be switched on or off by only tuning the pumping intensity or the detuning of the pump field from the exciton resonance. Simultaneously, we reveal that the bistability only exists in the strong SQD-DNA coupling regime. Specifically, we derive the matching relation between the excitatio...
