Self-assembled dielectric microlenses are used for focusing of the fluorescent signal emitted from a surface-based immunoassay, performed on silane micropatterns as assay substrates, to enhance the detection signal. In our model system, a fluorescent immunocomplex is formed on (3-aminopropyl)triethoxysilane (APTES) microstructures, and then carboxyl-functionalized melamine microparticles with two different sizes are electrostatically self-assembled on the microstructures. Mouse IgG diluted in phosphate buffered saline (PBS) is used as model target antigen and easily detected down to a concentration of 2 ng/mL. We also present a detailed two-dimensional numerical study using the Finite Element Method (FEM).