Ethoxy-silane modifications are usually straight forward (compared to methoxy). Silica NPs can be dispersed in a solution of APTES in EtOH. I would do this with a test batch (low concentration) and monitor the size increase of the particles with DLS and/or draw samples for SEM/TEM characterization.
Some add NH4OH (or HCl) to catalyze the hydrolyzation of the alkoxy groups.