We report here a straightforward nanoprecipitation-based process to prepare functionalized polylactide (PLA) nanoparticles (NPs). It relies on an organic phase containing a PLA-based amphiphilic copolymer bearing N-succinimidyl esters that can spontaneously react with a peptide/protein located in the aqueous phase. The relevance of this strategy is supported by an improved antigenicity of immobilized HIV-1 Gag p24 protein.