Self-assembled polymer/porous silicon nanocomposites overcome intracellular and systemic barriers for in vivo application of peptide nucleic acid (PNA) anti-microRNA therapeutics. Porous silicon (PSi) is leveraged as a biodegradable scaffold with high drug-cargo-loading capacity. Functionalization with a diblock polymer improves PSi nano particle colloidal stability, in vivo pharmacokinetics, and intracellular bioavailability through endosomal escape, enabling PNA to inhibit miR-122 in vivo.