A pH-insensitive fluorophore is made to give pH-driven responses through its covalent incorporation within a nanostructure derived from pH-responsive polymers. Fluorophore-shell-crosslinked nanoparticles (SCKs) demonstrate notable enhancement of photophysical properties, in the physiological pH region. Fluorophore-SCKs are designed to swell at higher pH and shrink as the pH is lowered, producing high fluorescence vs. low fluorescence outputs, respectively.