Fig. 1. (A) Schematic side view of the optical sensor utilizing the sensitive layer as the waveguide (not to scale). (B) Top view photograph of the functional sensor waveguide consisting of the secondary emitter zone (yellow), the analyte-sensitive zone with the immobilized indicator and the scattering spot (white). The optical isolation layer is deposited on the backside. (C) The sensor waveguide illuminated with a 460 nm LED. The overexposed white spot results from the LED light. The orange zone results from the emitted light guided and scattered at the scattering spot.