The method is provided for characterizing agglomeration of particles in a liquid containing an analyte, including introducing liquid into a fluid chamber; mixing the liquid with a bifunctional reagent, lighting the fluid chamber using an excitation light beam extending through the fluid chamber in a longitudinal direction (X); acquiring at least one image using a matrix photodetector, each image including pixels (In(x,y), x,y representing the coordinates of a pixel of an image, the image (I(x,y)) being formed by radiation transmitted by the lighted fluid chamber; and calculating from at least one acquired image (I(x,y)), at least one indicator (Ind2) characterizing the particle agglomeration. The photodetector can be positioned less than 1 cm from the fluid chamber, and during the calculation step, the calculated indicator (Ind2) is representative of the intensity of the pixels of the image. The method advantageously allows for charactering the agglomeration of particles in a liquid.