Methods and systems for point-of-care coagulation assays by optical detection

An assay system comprising:

• an excitation light source to output excitation light having a first wavelength;
• an optical reference positioned to absorb the excitation light from the excitation light source and to output an optical signal based on the excitation light, the optical signal having a second wavelength that is different from the first wavelength;
• a reaction chamber comprising a reactant and an inlet to receive a test sample to produce a fluid that is based on the test sample and the reactant, the reaction chamber being positioned to receive the optical signal from the optical reference;
• an optical receiver positioned to detect an amount of the optical signal that passed through the reaction chamber containing the fluid;
• wherein the optical reference is positioned between the excitation light source and the reaction chamber, and wherein the reaction chamber is positioned between the optical reference and the optical receiver;
• and
• a test instrument to detect an analyte or coagulation associated with the test sample based on the amount of the optical signal that passed through the reaction chamber containing the fluid.