Janus poly (N-isopropylacrylamide)-co-acrylic acid/Au microgels that resemble a “snowman”, “dumbbell”, and an “abalone” were prepared by thermally evaporating a layer of Au on half of the microgel surface, followed by exposure to thiolated single-stranded DNA with complementary sequences. We hypothesize that when the complementary single-stranded DNA attached to the Au forms the more stable double strand, the Au reorganizes on the microgel surface, yielding the observed unique Janus particle structures. Polymer, 2014 Schematic of the formation process of the hybrid Janus pNIPAm-co-AAc microgels. The microgels were either (A1, A2) directly coated with Au or (B1, B2) were coated with Au after modifying the microgels with a thiol group. The process includes directional coating of an Au layer on a single side of microgel and subsequent DNA modification. (Far right), SEM images of the corresponding Janus particles. (a) TEM image of the as-synthesized pNIPAm-co-AAc microgels, (b) SEM image of a single layer of microgels. As can be seen, the microgels flatten out on the Al substrate, protecting one side from Au deposition. The microgels are the large, rounded features in the SEM. PNIPAm-co-AAc microgels half-covered with a Au layer with varying thickness due to the different evaporation times of (a) 6, (b) 12, (c) 20 and (d) 30 s. (e) TEM images of microgels being evaporated for 12 s when varying the observing angles from −20°, 0° to 20°. This indicates successful directional modification of the microgels by Au in a high yield. The sample is obtained after removal of the microgels from the Al, but before DNA addition. The circle indicates the position of the Au cap. TEM images of Janus microgels after exposure to DNA. The microgels coated with Au with different evaporation time (a,b) less than 8 s, and (c,d) 20 s. The insets show cartoons of the related particles.
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