Figure 11.

Schematic representation of the real-time monitoring of ATP-responsive drug release from polypeptide-wrapped TDPA-Zn²⁺-UCNP@MSN.

Notes: Small molecule drugs were entrapped within the mesopores of the silica shell 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-vis emission from the multicolor UCNP under 980 nm of excitation was quenched because of the LRET between the loaded drugs and the UCNP. 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-vis 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 Lai J, Shah BP, Zhang Y, Yang L, Lee KB. Real-time monitoring of ATP-responsive drug release using mesoporous-silica-coated multicolor upconversion nanoparticles. ACS Nano. 2015;9(5):5234–5245. Copyright 2015 American Chemical Society.¹²²

Abbreviations: MSN, mesoporous silica nanoparticle; UV-vis, ultraviolet-visible; UCNP, up-conversion nanoparticle; TDPA-Zn²⁺, zinc-dipicolylamine analogue; Em, emission; LRET, luminescence resonance energy transfer; NIR, near infrared.