Optical sensor for bandage type monitoring device

A method comprising:

• operating a body-mountable device, wherein the body-mountable device comprises:
• a flexible substrate having a first side and a second side opposite the first side, wherein the flexible substrate is comprised by a single piece of material that is configured to be mounted to a skin surface and that is shaped to have an elongate extension having a distal end configured to extend beneath the skin surface to contact interstitial fluid;
• an adhesive layer disposed on the first side of the flexible substrate, wherein the adhesive layer is configured to adhere the flexible substrate to the skin surface;
• an optical fiber disposed on the elongate extension of the flexible substrate, wherein the optical fiber extends along a length of the elongate extension to the distal end of the elongate extension;
• an analyte-sensitive substance, wherein the analyte-sensitive substance is disposed at the distal end of the elongate extension of the flexible substrate, and wherein the analyte-sensitive substance has an optical property affected by an analyte in the interstitial fluid;
• a light detector;
• one or more electronic components disposed on the single piece of material of the flexible substrate, wherein at least one of the one or more electronic components is disposed on the first side of the flexible substrate;
• and
• a conductive trace patterned on a surface of the flexible substrate, wherein at least one of the one or more electronic components is connected to the flexible substrate via the conductive trace;
• wherein the operating comprises:
• obtaining, by the one or more electronic components operating the light detector to detect light emitted from the analyte-sensitive substance via the optical fiber, data related to a property of the emitted light;
• and
• indicating, by the one or more electronic components, the data related to the property of the emitted light.