A mega library of nanoparticles

US researchers say they have developed a way to produce 65,000+ types of complex nanoparticles, each containing up to six different materials and eight segments, with interfaces that could be exploited in electrical or optical applications. 

It’s a simple approach, using straightforward chemistry and a mix-and-match, modular strategy – but the resulting nanoparticles, they say, are among the most complex ever made. 

Each is about 55 nanometres long by 20 wide: by comparison, a human hair is about 100,000 nanometres thick.

“There is a lot of interest in the world of nanoscience in making nanoparticles that combine several different materials – semiconductors, catalysts, magnets, electronic materials,” says Raymond E Schaak, who led the team from Pennsylvania State University

“You can think about having different semiconductors linked together to control how electrons move through a material or arranging materials in different ways to modify their optical, catalytic or magnetic properties. 

“We can use computers and chemical knowledge to predict a lot of this, but the bottleneck has been in actually making the particles, especially at a large-enough scale so that you can actually use them.”

The new method – described in a paper in the journal Science – goes a bit like this.

Schaak and colleagues took simple nanorods composed of copper and sulfur then sequentially replaced some of the copper with other metals using a process called cation exchange. 

By altering the reaction conditions, they could control where in the nanorod the copper was replaced (one end, both ends simultaneously or in the middle). They repeated the process with other metals, which could also be placed at precise locations within the nanorods. 

By performing up to seven sequential reactions with several different metals, they could create a rainbow of particles – more than 65,000 combinations of metal sulfide materials are possible.

“It used to take months or years to make even one type of nanoparticle that contains several different materials,” says first author Benjamin C Steimle. 

“Two years ago, we were really excited that we could make 47 different metal sulfide nanoparticles using an earlier version of this approach.” 

Now, things have changed. “We can produce nanoparticles with previously unimaginable complexity simply by controlling temperature and concentration, all using standard laboratory glassware and principles covered in an introductory chemistry course.”

Schaak acknowledges there are limitations at this stage but says there is great potential because the method is “rational and scalable”.

“Because we understand how everything works, we can identify a highly complex nanoparticle, plan out a way to make it, and then go into the laboratory and actually make it quite easily. And, these particles can be made in quantities that are useful.”