Stephanie Christau

Polymer Brush/Metal Nanoparticle Hybrids for Optical Sensor Applications: from Self-Assembly to Tailored Functions and Nanoengineering

Abstract This review article summarizes the progress of research in the field of polymer brush/metal nanoparticle hybrid materials. We will discuss the mutual influence of polymer brush matrix and particles. Self-assembly of particles within polymer brushes, and ways to control the loading and location of nanoparticles inside polymer brushes will be described, as well as the possibility to use the brush templates as nanoreactors to generate metal nanoparticles. The combination of stimuli-responsive polymer brushes and nanoparticles exhibiting surface plasmon resonance, such as gold or silver, enables the design of optical sensors based on reversible variations of the brush conformation. Sensing devices are capable of detecting a variety of extrinsic variations in their surrounding enviroments. The progress in the development of such optical sensors using brush/particle hybrids will be discussed in more detail.

Uptake of pH-Sensitive Gold Nanoparticles in Strong Polyelectrolyte Brushes

The impact of electrostatic attraction on the uptake of gold nanoparticles (AuNPs) into positively charged strong poly-[2-(Methacryloyloxy) ethyl] trimethylammonium chloride (PMETAC) polyelectrolyte brushes was investigated. In this work, PMETAC brushes were synthesized via surface-initiated atom transfer radical polymerization (Si-ATRP). PMETAC/AuNP composite materials were prepared by incubation of the polymer brush coated samples into 3-mercaptopropionic acid-capped AuNP (5 nm in diameter) suspension. The electrostatic interactions were tuned by changing the surface charge of the AuNPs through variations in pH value, while the charge of the PMETAC brush was not affected. Atomic-force microscopy (AFM), ellipsometry, UV/Vis spectroscopy, gravimetric analysis and transmission electron microscopy (TEM) were employed to study the loading and penetration into the polymer brush. The results show that the number density of attached AuNPs depends on the pH value and increases with increasing pH value. There is also strong evidence that the particle assembly is dependent on the pH value of the AuNP suspension. Incubation of PMETAC brushes in AuNP suspension at pH 4 led to the formation of a surface layer on top of the brush (2D assembly) due to sterical hindrance of the clustered AuNPs, while incubation in AuNP suspension at pH 8 led to deeper particle penetration into the brush (3D assembly). The straightforward control of particle uptake and assembly by tuning the charge density of the nanoparticle surface is a valuable tool for the development of materials for colorimetric sensor applications.