Fig. 1.

Preparation and characterization of APP^Gd-Cy5, APP^Gd-Cy7, and APP^Gd-DOX prodrug. A Schematic synthesis route of APP. B Chemical structure of APP^Gd-Cy5. C–H The absorption and fluorescence spectra of APP^Gd-Cy5, APP^Gd-Cy7, and APP^Gd-DOX prodrug at various concentrations (2.5–10 μM). I The cumulative release of DOX from the APP^Gd-DOX prodrug was observed following incubation at pH levels of 7.4, 6.5, 6.0, and 5.0, respectively