Gold-plated nanocellulose shows its colors

GoldPlatedNanocelluloseShowsItsColors
Novel composites of nanocellulose and metal nanoparticles could prove of use for various optical, catalytic, electrical and biomedical applications

Original source: Materials Today

Researchers have found that combining nanocellulose with various types of metal nanoparticles can produce materials with many new and exciting properties. They may be antibacterial, change color under pressure or convert light into heat.

“To put it simply, we make gold from nanocellulose,” says Daniel Aili, associate professor in the Department of Physics, Chemistry and Biology at Linköping University in Sweden.

Aili and his research group took a biosynthetic nanocellulose produced by bacteria and originally developed for wound care, and decorated it with metal nanoparticles, principally silver and gold. The nanoparticles are first tailored to give them certain desired properties and then combined with the nanocellulose.

“Nanocellulose consists of thin threads of cellulose, with a diameter approximately one thousandth of the diameter of a human hair,” explains Aili. “The threads act as a three-dimensional scaffold for the metal particles. When the particles attach themselves to the cellulose, a material that consists of a network of particles and cellulose forms.”

The researchers can determine with high precision how many particles will attach, and their identities. They can also mix particles made from different metals and with different shapes – spherical, elliptical and triangular. In a paper in Advanced Functional Materials, the group describes the process and explains why it works as it does, before going on to discuss several areas of application.

One exciting phenomenon is the way in which the properties of the material change when pressure is applied. As pressure pushes the particles together and causes them to interact, the material changes color, until the material eventually appears to be gold. “We saw that the material changed color when we picked it up in tweezers, and at first we couldn’t understand why,” says Aili.

The scientists have named the phenomenon ‘the mechanoplasmonic effect’, and it has turned out to be very useful. A potential application is in sensors, where the effect would allow sensors to be read with the naked eye. For example, a protein sticking to the material can prevent it from changing color when placed under pressure. If the protein is a marker for a particular disease, the failure to change color can be used in diagnosis. If the material changes color, the marker protein is not present.

Another interesting phenomenon is displayed by a variant of the material that can absorb light from a broad spectrum of visible light and then generate heat. This property can be used for both energy-based applications and in medicine.

“Our method makes it possible to manufacture composites of nanocellulose and metal nanoparticles that are soft and biocompatible materials for optical, catalytic, electrical and biomedical applications. Since the material is self-assembling, we can produce complex materials with completely new well-defined properties,” Aili says.