DNA barcodes have analyzed nanoparticle delivery in vivo. (A) Chemically diverse LNPs are tagged with unique DNA barcodes. LNPs were pooled together and administered both in vitro and in vivo. For in vitro studies, delivery at condition 1 often correlates with delivery at condition 2. However, in vitro delivery does not correlate to in vivo delivery. These results were consistent across many cell types, and across different experiments, for >300 different LNPs [33]. (B) Liposomes carrying different chemotherapies were formulated with unique barcodes. After administering the liposomes in vivo, tissues were removed and cells were stained with propidium iodine (PI), which distinguishes dead cells from live cells. Barcodes enriched in dead cells corresponded to successful chemotherapy agents.