Figure 13.

Schematic representation of the real-time monitoring of ATP-responsive drug release from polypeptide wrapped TDPA-Zn²⁺-UCNP@MSNs. Small molecule drugs were entrapped within the mesopores of the silica shell on the nanoparticle by branched polypeptide capping the pores through a multivalent interaction between the oligo-aspartate side chain in the polypeptide and the TDPA-Zn²⁺ complex on nanoparticles surface. The UV–visible emission from the multicolor UCNP under 980 nm excitation was quenched because of the LRET between the loaded drugs and the UCNP. The addition of small molecular nucleoside-polyphosphates such as ATP led to a competitive binding of ATP to the TDPA-Zn²⁺ complex, which displaced the surface bound compact polypeptide because of the high binding affinity of ATP to the metallic complex. The drug release was accompanied with an enhancement in the UV–visible emission of UCNP, which allows for real-time monitoring of the drug release via a ratiometric signal using the NIR emission of UCNP as an internal reference. Reprinted with permission from Ref¹⁸⁷. Copyright (2015) American Chemical Society.