In chemiluminescent EIA, the detection signal comes from?

• A. absorption of light
• B. gamma radiation
• C. emission of light by a chemical reaction
• D. fluorescence from a dye

Answer: (C)

Light is produced directly by a chemical reaction in chemiluminescent EIA. The detection signal comes from the emission of photons as a chemical reaction proceeds, not from external light or from absorbing light. In practice, an enzyme such as horseradish peroxidase catalyzes oxidation of a luminescent substrate, creating an excited intermediate that releases light as it returns to its ground state. This emitted light is measured and correlates with the amount of target analyte. This is different from absorption-based methods, which rely on light blocking or reduction; and from fluorescence, which requires external light to excite a dye and then emits light. Gamma radiation is not involved in this signal generation.