A tissue sensing device for use with an electrosurgical knife is proposed which comprises a proximal end portion, a distal end portion and a grip portion there between. The proximal end portion is configured for attachment to a housing of the electrosurgical knife. The distal end portion is configured for movably supporting a blade of the knife. A distal end of an optical fiber is arranged at the distal end portion of the device and a proximal end of the optical fiber is connectable to an optical console, so that optical measurements can be performed at the distal end portion.