Environmentally responsive hydrogels have become attractive research subjects for many applications. In this work, a series of pH-sensitive and color-changing nanoparticles (nanogels) with core-shell structures were synthesized. The cores were blue latex particles synthesized by a miniemulsion technique with styrene and methacrylic acid as monomers and Neozapon Blue 807 as a dye. The shell was a pH-sensitive polymer that was precipitation-polymerized onto the core from 2-(diethylamino) ethyl methacrylate with N,N'-methylenebisacrylamide, poly(propylene glycol) diacrylate, and divinylbenzene as crosslinking agents. In the resultant latexes, the color was observed to change from deep blue to pate blue as the pH of the system was changed from a high of 10 to a low of 3. The synthesized latexes and particles (gels) were then characterized with an ultraviolet-visible spectrometer, dynamic light scattering, Fourier transform infrared, and nuclear magnetic resonance. Atomic force microscopy was also used to investigate the different morphologies of the particles after the synthesized latexes were dried at different pH values. (c) 2007 Wiley Periodicals, Inc.