Upconversion nanoparticle-based fluorescence resonance energy transfer sensing of programmed death ligand 1 using sandwich epitope-imprinted polymers.

Programmed death ligand 1 (PD-L1) has been shown to suppress the anti-tumor immune response of some lung cancer patients, and thus PD-L1 expression may be a valuable predictor of the efficacy of anti-PD-1/PD-L1 monoclonal therapy in such patients. In this work, a sandwich approach to fluorescence resonance energy transfer (FRET) was used with green-emitting Yb/Ho-doped upconversion nanoparticles (UCNPs) and a rhodamine-conjugated conductive polymer as donor and acceptor, respectively. Yb/Ho-doped UCNPs were synthesized and then coated with poly(ethylene-co-vinyl alcohol), pEVAL, imprinted with PD-L1 peptide. Epitope-imprinted composite nanoparticles were characterized by dynamic light scattering, superconducting quantum interference magnetometry, and atomic force microscopy. Poly(triphenylamine rhodamine-3-acetic acid-co-3,4-ethoxylenedioxythiophene)s copolymers (p(TPAR-co-EDOT)) were imprinted with various epitopes of PD-L1 by in situ electrochemical polymerization. The epitope-imprinted polymer-coated electrodes were then characterized by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Finally, the sandwich sensing of various PD-L1 concentrations with peptide-imprinted p(TPAR-co-EDOT)-coated substrate and UCNP-containing magnetic peptide-imprinted pEVAL nanoparticles by FRET was conducted to measure the concentration of PD-L1 in A549 lung cancer cell lysate.