Hokkaido University Research Profiles

Nanotechnology / Materials

Stabilization of Nanoparticles Using Cyclic Poly(ethylene Glycol)

A novel stabilization method relying on the “topology” of polymers

In this research, we developed a novel dispersion stabilization method for metal nanoparticles using cyclic poly(ethylene glycol). The research group has found that molecular aggregates consisting of cyclic polymers have excellent stability. By applying this phenomenon, the dispersion stability of nanoparticles can be enhanced.

Content of research

A large number of nanoparticle-based drugs are currently investigated, including drug delivery system (DDS) carriers, many of their surface is covered with biocompatible poly(ethylene glycol) (PEG). In this regard, we have found that gold nanoparticles (AuNPs) modified with cyclic PEG exhibit high dispersion stability at high salt concentrations. In other words, AuNPs treated with cyclic PEG with a molecular weight of 4000 retained their dispersion stability for one week or longer in a 180 mM NaCl solution, which is a higher concentration than physiological conditions, whereas AuNPs treated with linear PEG of the same molecular weight started aggregating and precipitating within 3 hours in a solution of only 45 mM NaCl. This novel method using cyclic PEG can be applied to a variety of nanoparticle-based drugs including contrast agents and magnetic nanoparticles.

  • Stability evaluation of gold nanoparticles (AuNPs). In the case of cyclic PEG is used, the dispersion stability is good, and the wavelength of the surface plasmon is maintained (522 nm). However, in the case of ordinary linear PEG is used, the wavelength changes to a longer wavelength (547 nm) due to aggregation of AuNPs. Transmission electron microscopy images also show the dispersion of AuNPs when cyclic PEG is used and aggregation when linear PEG is used.

Potential for social implementation

  • ・Biosensors
  • ・Intracellular probe
  • ・Drug delivery material
  • ・Optical contrast material
  • ・Therapeutic agents using the photothermal effect

Appealing points to industry and local governments

This research focused on the drastically changing properties of polymers by efficiently switching between linear and cyclic topologies using only one chemical reaction per polymer chain without changing the chemical structure or molecular weight of the polymer itself. Since this is not a chemical modification of the repeating units of the polymer, it is widely applicable to the enhancement of the functionality of existing polymer materials. In addition, there are almost no concerns about toxicity or environmental pollution.