A method for optically detecting biomarkers in a biosensor is disclosed, wherein the optical detection obtains spatially and spectrally resolved optical signals from a sample on a biosensor, and one or more of these spatially and spectrally resolved optical signals can be analyzed in parallel with image acquisition. The image analysis comprises reading data of the acquired images, correcting them to reduce inhomogeneities and noise, localizing particles in the images, characterizing each particle individually to obtain its position and characterization parameters, and classifying the particles based on their characterization parameters. Using the number of particles per class for all the acquired images of the sample, a statistical value is calculated per sample and each statistical value is correlated with an indication of the presence of a biomarker in the sample.