Measuring cassette and measuring device for the detection of target molecules in a liquid sample by measurement of fluorescence emission after excitation in an evanescent field

A measuring system for the detection of target molecules in a liquid sample by measurement of fluorescence emission after excitation in an evanescent field, comprising:

• a measuring device;
• and
• a plurality of replaceable measuring cassettes, each replaceable measuring cassette comprising:
• a body of an optically transparent material having an upper-side, an under-side, and a surface providing a light entry area where excitation radiation provided by the measuring device enters into the body, wherein, when introduced into the measuring device, the upper side faces a top portion of the measuring device and the under-side faces a bottom portion of the measuring device;
• a base contacting the under-side of the body;
• a microfluidic structure formed by a combination of recesses in the body and in the base that contains a liquid sample that is moveable within the microfluidic structure, wherein the microfluidic structure comprises a flow-through measuring cell and at least one of the following arrangements a) to c):
• a) a zone for dissolving a tracer;
• b) a sample mixing region, or c) a liquid detection region, wherein the flow-through measuring cell is a recess within the microfluidic structure in which excitation radiation provided by the measuring device generates an evanescent field in the liquid sample on a base material side of a boundary surface of the liquid sample and the measuring cell;
• areas on which the body and the base contact each other and surround the recess forming the microfluidic structure are bonded to one another directly and in a fluid-tight manner by laser welding;
• and
• several different trapping zones provided in the measuring cell and configured to respond to several different analytes at the various trapping zones using only one light source,
• wherein the surface of the body providing the light entry area forms a converging lens which always directs the beam of the excitation radiation centrally along the longitudinal axis of the measuring cell exactly to the desired point of the boundary surface of the liquid sample and the surface of the transparent material of the body at which the fluorescence emission to be measured is to be generated,
• wherein the measuring device comprises:
• an insertion shaft configured to receive one of the plurality of replaceable measuring cassettes at a time;
• and
• a holder configured to provide a relative movement of the one of the plurality of replaceable measuring cassettes with respect to the light source for the excitation radiation, in order to bring various regions of the measuring cell into the beam path of the excitation radiation and to be able to respond to several different analytes in several different trapping zones provided in the measuring cell using only one light source;
• a light source that creates an excitation radiation, which is arranged in the measuring device such that the beam of the excitation radiation meets the measuring cell at an angle of 90 degrees to the direction of the relative movement of the measuring cassette with respect to the light source;
• and
• a detector arranged on the top portion of the measuring device and configured to detect the evanescent field.