This article describes an original strategy to enable solid-phase oligodeoxyribonucleotide (ODN) synthesis on nanosized silica particles. It consists of the reversible immobilization of silica nanoparticles (NPs) on micrometric silica beads. The resulting assemblies, called nano-on-micro (NOM) systems, are well adapted to ODN synthesis in an automated instrument. First, NPs are derivatized with OH functions. For NOM assembly preparation, these functions react with the silanols of the microbeads under specific experimental conditions. Furthermore, OH groups allow ODN synthesis on the nanoparticles via phosphoramidite chemistry. The stability of the NOM assemblies during ODN solid-phase synthesis is confirmed by scanning and transmission electron microscopy (SEM and TEM, respectively), together with dynamic light scattering analyses. Then, the release of ODN-functionalized nanoparticles is performed tinder mild conditions (1% NH4OH in water, 1 h, 60 degrees C). Our technique provides silica nanoparticles well functionalized with oligonucleotides, as demonstrated by hybridization experiments conducted with the cDNA target.