An end effector includes first and second jaw members moveable relative to one another. Each of the first and second jaw members including a tissue contacting surface opposing the tissue contacting surface of the other jaw member. The end effector includes a detection assembly that is disposed within the first or second jaw member that is configured to detect an attribute of tissue between the first and second jaw members. The detection assembly may include a light source configured to emit light towards tissue between the first and second jaw members or may include an ultrasound transducer configured to emit ultrasound energy towards tissue between the first and second jaw members.