Patent ID: 8535609

Claim:
A test element for the analytical investigation of a liquid sample, comprising: a carrier film having an elongated, strip-shaped form, the carrier film comprising: a first light guide layer having a flat side and an opposed second side, said first light guide layer further comprising an entry surface for coupling in primary light, a second light guide layer positioned adjacent to the second side of said first light guide layer and opposite of the flat side, the second light guide layer extending along the longitudinal dimension of the first light guide layer, and a coupling out zone which is part of the flat side of the first light guide layer; and a test field secured to the flat side of the first light guide layer, the test field constructed and arranged to receive a liquid sample, wherein liquid sample components penetrate into the test field, the test field comprising: a reagent system comprising a soluble reagent capable of causing an optically measurable change upon reaction with an analyte of the liquid sample, the optically measurable change being characteristic for the analysis, and a detection zone in optical contact with the coupling out zone in such a manner that the primary light is coupled out from the first light guide layer into the detection zone such that the primary light illuminates the detection zone, the optically measurable change being measured by illuminating the detection zone with the primary light and detecting an intensity of secondary light, said secondary light comprising light that has been reflected at the detection zone; wherein the entry surface couples in primary light in such a manner that the first light guide layer provides a first light guide section for the light path of the primary light coupled into the first light guide layer from the entry surface toward the detection zone, the first light guide section running inside the first light guide layer along the longitudinal dimension of the carrier film; and wherein the secondary light is reflected from the detection zone and into the second light guide layer, and the second light guide layer is constructed and arranged to provide a second light guide section for the light path of the secondary light away from the detection zone, the second light guide section running along the longitudinal dimension of the carrier film and adjacent to the first light guide section.