ORIGINAL PAPER An antibacterial composite system based on multi-responsive microgels hosting monodisperse gold nanoparticles Damla Ulker 1 & Cansel Tuncer 2 & Serife B. Sezgin 1 & Yagmur Toptas 3 & Ahmet Cabuk 4 & Vural Bütün 1,2 Received: 2 March 2017 /Accepted: 20 September 2017 # Springer Science+Business Media B.V. 2017 Abstract A multi-responsive microgel having response to pH, temperature, and salt concentration was successfully prepared using a water-soluble monomer. Microgels were readily pre- pared from 2-(N-morpholino)ethyl methacrylate (MEMA) via emulsion polymerization using glycidyl methacrylate as a como- nomer cross-linker. The morpholino groups of MEMA residues of microgels were able to give complexation with metal contain- ing anions such as AuCl 4 - in acidic conditions. The reduction of aurate ions with sodium borohydride led to immobilized-gold nanoparticles (AuNP) in the microgel system. Average particle diameters of AuNPs were determined to be 10 ± 2 nm. The resulting AuNP-microgel system was examined as a nanoreactor for catalyst system and determined to be very effective in the reduction of 4-nitrophenol model reaction in aqueous media. AuNPs-microgel composite system had antibacterial properties against several Gram-positive and Gram-negative bacteria simi- lar to amoxicillin. This P(MEMA-co-GMA) microgel is also very useful for different applications such as a host for metal nanoparticle production, a drug carrier or drug delivery system. Keywords Microgels . Metal nanoparticles . Composites . Catalytic effect . Antibacterial . Responsive systems Introduction Polymeric gels are in the group of smart materials, which are microgel and hydrogel, they respond to ex- ternal stimuli by changing their size. Microgels com- prise chemical cross-linked spherical polymer particles [1–3]. Additionally, such smart materials show good biocompatibility, excellent (de)swelling properties, vari- ous sizes, and large surface areas [1]. Microgels can be sensitive to various stimuli depending on type of mono- mers used in the synthesis. Their response can vary with light, quality of solvent, electrolyte concentration, temperature 4, 5], and solution pH [6, 7]. They can be classified in three main categories, thermo-, pH- and salt- responsive microgels. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10965-017-1336-y) contains supplementary material, which is available to authorized users. * Vural Bütün vbutun@ogu.edu.tr Damla Ulker damlaulker@gmail.com Cansel Tuncer ctasagir@ogu.edu.tr Serife B. Sezgin betulbaker88@gmail.com Yagmur Toptas yagmurtoptas@gmail.com Ahmet Cabuk acabuk@ogu.edu.tr 1 Department of Polymer Science and Technology, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey 2 Department of Chemistry, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey 3 Department of Biology, Graduate School of Natural and Applied Sciences, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey 4 Department of Biology, Eskisehir Osmangazi University, 26480 Eskisehir, Turkey J Polym Res (2017) 24:169 DOI 10.1007/s10965-017-1336-y