Tunable Photolumineseence of Ag Nanocrystals in Multiple-Sensitive Hybrid Microgels

We report here fluorescent pH-sensitive hybrid materials based oil the in situ immobilization of Ag and Ag/Au bimetallic nanciparticles (NPs) in the interior of multiple sensitive copolymer microgels of poly(N-isopropylacrylamide-co-acrylic acid-co-acrylamide) with polyacrylamide fragments serving as stabilizing ligands. Temperatures corresponding to the swollen, partially swollen, and nearly collapsed states of the template microgels were respectively applied for loading and in situ chemical reduction of Ag+ ions to control the size and size distribution of the Ag NPs in the microgels. Au nanoclusters were stably grown on the surface of Ag NPs through a galvanic replacement reaction between Ag and AuCl4-. The pH-sensitive optical properties of hybrid microgels embedded with either Ag NPs or Ag/Au bimetallic NPs Were systematically investigated. The gradual protonization of poly(acrylic acid) fragments shrank the microgels, resulting in an enhancement of photoluminescence (PL) intensity and a blue shift of the emission maximum of the Ag NPs. The surface modification of small Ag NPs with Au nanoclusters reduced the pH sensitivity of PL property changes but dramatically enhanced the PL signals in the near-infrared regime of the hybrid microgels. The method presented here opens a new door in the synthesis of materials with pH-responsive optical properties for biomedical applications.