A device comprising: a polymeric material having a body-mountable surface formed to be mounted to a body surface; a first substrate (230, 540) at least partially embedded within the polymeric material; a conductive interconnect (251, 548) disposed on the first substrate; an electrochemical sensor (260, 560) disposed on the first substrate, the electrochemical sensor comprises: a sensor substrate (510, 562) different from and having a greater rigidity than the first substrate, wherein the sensor substrate includes a first side and a second side opposite the first side; a working electrode (520, 570) disposed on the first side of the sensor substrate; a reference electrode (530, 580) disposed on the first side of the sensor substrate; a first conductive connection pad (522, 552) disposed on the second side of the sensor substrate, wherein the first conductive connection pad is electrically coupled to the working electrode; and a second conductive connection pad (532, 558) disposed on the second side of the sensor substrate, wherein the second conductive connection pad is electrically coupled to the reference electrode; and a controller electrically connected to the electrochemical sensor via the first and second conductive connection pads, wherein the controller is electrically connected to the first conductive connection pad via the interconnect, wherein the controller is disposed on the first substrate, and wherein the controller is configured to: (i) apply a voltage between the working electrode and the reference electrode sufficient to generate an amperometric current related to the concentration of an analyte in a fluid to which the device is exposed, and (ii) measure the amperometric current. a polymeric material having a body-mountable surface formed to be mounted to a body surface; a first substrate (230, 540) at least partially embedded within the polymeric material; a conductive interconnect (251, 548) disposed on the first substrate; an electrochemical sensor (260, 560) disposed on the first substrate, the electrochemical sensor comprises: a sensor substrate (510, 562) different from and having a greater rigidity than the first substrate, wherein the sensor substrate includes a first side and a second side opposite the first side; a working electrode (520, 570) disposed on the first side of the sensor substrate; a reference electrode (530, 580) disposed on the first side of the sensor substrate; a first conductive connection pad (522, 552) disposed on the second side of the sensor substrate, wherein the first conductive connection pad is electrically coupled to the working electrode; and a second conductive connection pad (532, 558) disposed on the second side of the sensor substrate, wherein the second conductive connection pad is electrically coupled to the reference electrode; and a sensor substrate (510, 562) different from and having a greater rigidity than the first substrate, wherein the sensor substrate includes a first side and a second side opposite the first side; a working electrode (520, 570) disposed on the first side of the sensor substrate; a reference electrode (530, 580) disposed on the first side of the sensor substrate; a first conductive connection pad (522, 552) disposed on the second side of the sensor substrate, wherein the first conductive connection pad is electrically coupled to the working electrode; and a second conductive connection pad (532, 558) disposed on the second side of the sensor substrate, wherein the second conductive connection pad is electrically coupled to the reference electrode; and a controller electrically connected to the electrochemical sensor via the first and second conductive connection pads, wherein the controller is electrically connected to the first conductive connection pad via the interconnect, wherein the controller is disposed on the first substrate, and wherein the controller is configured to: (i) apply a voltage between the working electrode and the reference electrode sufficient to generate an amperometric current related to the concentration of an analyte in a fluid to which the device is exposed, and (ii) measure the amperometric current. (i) apply a voltage between the working electrode and the reference electrode sufficient to generate an amperometric current related to the concentration of an analyte in a fluid to which the device is exposed, and (ii) measure the amperometric current.