Temperature-Dependent Optical Properties of Gold Nanoparticles Coated with a Charged Diblock Copolymer and an Uncharged Triblock Copolymer

Abstract

We demonstrate that the optical properties of gold nanoparticles can be used to detect and follow stimuli-induced changes in adsorbed macromolecules. Specifically, we investigate thermal response of anionic diblock and uncharged triblock copolymers based on poly(N-isopropylacrylamide) (PNIPAAM) blocks adsorbed onto gold nanoparticles and planar gold surfaces in a temperature range between 25 and 60 degrees C. By employing a palette of analytical probes, including UV-visible spectroscopy, dynamic light scattering, fluorescence, and quartz crystal microbalance with dissipation monitoring, we establish that while the anionic copolymer forms monolayers at both low and high temperature, the neutral copolymer adsorbs as a monolayer at low temperatures and forms multilayers above the cloud point (T(C)). Raising the temperature above T(C) severely affects the optical properties of the gold particle/polymer composites, expelling associated water and altering the immediate surroundings of the gold nanoparticles. This effect, stronger for the uncharged polymer, is related to the amount of polymer adsorbed on the surface, where a denser shell influences the surface plasmon band to a greater degree. This is corroborated with light scattering experiments, which reveal that flocculation of the neutral polymer-coated particles occurs at high temperatures. The flocculation behavior of the neutral copolymer on planar gold surfaces results in multilayer formation. The observed effects are discussed within the framework of the Mie-Drude theory.

Nanoplasmonic sensing for nanomaterials science

“…In 2010 Volden et al showed that refractive index based sensing of changes in polymers can also be made on nanoparticles that are not located on a surface [45] . They used anionic diblock and uncharged triblock copolymers adsorbed onto gold nanoparticles and monitored the temperature response of the polymers.…”

A new plasmonic device made of gold nanoparticles and temperature responsive polymer brush on a silicon substrate

“…These applications indicated a robust changing of the SERS signals depending on the distance between Au or Ag NPs and on Au flat surface. Others have reported the plasmon band changing of Au and Ag NPs coated on top of pH or solvent sensitive polymer brushes [12][13][14][15][16][17]. However, to best of our knowledge, optimization of the Raman signals resulted from changing of the distance between Au NPs on a temperature responsive poly[(2-methoxyethoxy)ethyl) methacrylate] [poly(MEO 2 -MA)] brush layer has never been reported so far.…”

Surface design with self-heating smart polymers for on–off switchable traps

“…Their properties can be changed by external stimuli such as temperature [1,2], light [3,4], electric and magnetic fields [5][6][7], ionic strength [8], pH [9] and chemicals [10,11]. Therefore, smart polymers are used in biotechnology, medicine and engineering, in such applications as drug delivery systems [12][13][14], chemical separation [15,16], sensors [17] and actuators [18,19]. The smart polymer that has been studied most extensively is poly(N-isopropylacrylamide) (PNIPAAm) [20][21][22][23][24][25].…”