Optically pH and H2O2 Dual Responsive Composite Colloids through the Directed Assembly of Organic Dyes on Responsive Microgels

A novel type of smart composite materials based on the directed assembly of organic dyes on a responsive microgel template was prepared and investigated. We have chosen Calcon, a monoazo dye, as model organic dye molecules and the copolymer microgel of poly(N-isopropylacrylamide-acrylic acid-acrylamide) [p(NIPAM-AA-AAm)] as template with the pAA segments designed for inducing pH-sensitivity and the pAAm segments designed for directing the highly ordered assembly of dye molecules. Transmission electron microscopy, X-ray scattering, and light scattering were used to study the dye assembling structures and the pH-induced volume phase transitions of the composite microgels. The UV-vis absorption. and photoluminescence properties of the composite microgels were respectively investigated at different pH values and H2O2 concentrations. The pH-induced shrinkage of the template microgels not only results in a systematic shift in the wavelength of bands, but also significantly increases the absorption and emission intensity. The composite microgels also exhibit a highly H2O2-sensitive fluorescence quenching. The pAAm-directed highly ordered assembling structure of dye molecules is critical to produce the unique pH/H2O2 dual responsive optical properties, which may find important applications in bioimaging and biosensing.