Abstract: This method for estimating the quantity of an analyte contained in a liquid includes the following steps: introducing the liquid into a fluid chamber; mixing the liquid with a bi-specific reagent, the bi-specific reagent being configured for grafting on both a particle and an analyte present in the liquid; lighting the fluid chamber using an excitation beam emitted by a light source, the beam extending through the fluid chamber; acquiring at least one image using a matrix photodetector, the image being formed by radiation transmitted by the lighted fluid chamber; and estimating, from at least one acquired image, the quantity of said analyte in the liquid.