Major Goals: Aim 1. To validate and improve the application of selected known brain-targeting molecules to nanoparticle CNS delivery, using the Q? virus-like particle as the proof-of-concept platform. Aim 2. To assess the immunogenicity, toxicity, and effects on BBB integrity of selected optimized nanoparticles from Aim 1 (and later Aim 3). Only those particles and formulations that result in no damage to the BBB (or transient disruption of the BBB that do not allow access of harmful agents) will be considered for further study and optimization. Aim 3. To discover nanoparticle motifs with generalized brain-targeting function by a biopanning strategy involving multiple phage display platforms in vivo.