The invention relates to a sensor for sensing an analyte. The sensor comprises a detection sensing element having an electrical property variable with the amount of optical light received by the detection sensing element, a control sensing element having an electrical property variable with the amount of optical light received by the control sensing element, a detection optical element for contacting an analyte and transmitting a first amount of optical light received thereby to the detection sensing element in response to the contact with the analyte, a control optical element for contacting a control medium and transmitting a second amount of optical light received thereby to the control sensing element in response to the contact with the control medium, and an output arrangement configured to provide an indication based on the electrical property of the detection sensing element when the first amount of optical light is received by the detection sensing element, with respect to the electrical property of the control sensing element when the second amount of optical light is received by the control sensing element, thereby sensing said analyte. In various embodiments, the sensor is a pH sensor and electrical resistance is the electrical property variable in response to the amount of optical light received by the sensing elements.