Table 1.
Summary of the different gatekeepers described in the previous sections and whether they are targeted.
| Gatekeeper | Targeted [X/✔ (Targeting Agent)] | Target | References |
|---|---|---|---|
| ANTIBODIES, APTAMERS, PEPTIDES AND PROTEINS | |||
| Keratin | X | - | [16] |
| Albumin; Myoglobin | X | - | [21] |
| Poly(γ-benzyl-L-glutamate) | ✔ (folic acid) | Folic acid receptor | [37] |
| Poly-L-histidine | ✔ (folic acid) | Folic acid receptor | [38] |
| Anti-carbonic anhydrase IX antibody | ✔ (gatekeeper) | Carbonic anhydrase IX | [43] |
| AS1411 aptamer | ✔ (gatekeeper) | Nucleolin protein | [44] |
| Amphiphilic peptide | ✔ (RGD) | αβ-integrins | [45] |
| Ferritin | ✔ (gatekeeper) | TRf1 receptor | [46] |
| Transferrin | ✔ (gatekeeper) | TRf1 receptor | [47,48] |
| POLYMERS | |||
| Polydopamine | X | - | [18] |
| Dextrin | X | - | [19] |
| Gelatin | X | - | [20] |
| Chitosan | X | - | [23] |
| ✔ (folic acid) | Folic acid receptor | [36] | |
| Polyethylene imine | ✔ (gatekeeper masked with citraconic anhydride) | Exposition of positive charge | [41] |
| Polylysine | ✔ (gatekeeper masked with citraconic anhydride) | Exposition of positive charge | [42] |
| SMALL NANOPARTICLES | |||
| ZnO quantum dots | X | - | [28] |
| Graphene quantum dots | X | - | [29] |
| Au NPs | X | - | [30] |
| ✔ (folic acid) | Folic acid receptor | [40] | |
| SMALL MOLECULES | |||
| Tryptophan-containing small molecule | X | - | [22] |
| Self-immolative carbamate | ✔ (biotin) | Biotin receptor | [35] |
| CARBOHYDRATES | |||
| Chondroitin sulfate | ✔ (gatekeeper) | CD44 receptor | [49] |
| Hyaluronic acid | ✔ (gatekeeper) | CD44 receptor | [50,51,52,53] |
| NANOVALVES | |||
| Cucurbit[6]uril | X | - | [25] |
| Cyclodextrin | X | - | [26] |
| X | - | [27] | |
| ✔ (galactose) | Asialoglycoprotein receptor | [34] | |
| ✔ (folic acid) | Folic acid receptor | [39] | |