We have chemically modified the frustules of the marine diatom Coscinodiscus concinnus Wm. Smith to properly bind a highly selective bioprobe such as an antibody. By measuring the changes in the photoluminescence emission of diatoms frustules, we have monitored the molecular recognition event between the antibody and its ligand: the dissociation constant estimated is of the same order of that measured by standard Biacore®. The nanostructured silica frustules, a low-cost and natural available material, have shown high sensitivity, equal to 1.2 ± 0.2 nm μM−1, and a detection limit of 100 nM, and thus are quite ideal candidates for lab-on-particle applications.