Did you make any scientific breakthroughs while you were in Berlin?

There were a number of scientific breakthroughs that have been considered as significant. Some were basically on how to modify colloid particles – even very, very small particles in the nanometre regime, between about 50 x 10^-9 metres and about 100 nanometres in diameter. We developed a very versatile and flexible strategy to modify the surfaces of these particles and introduce new functionalities to them, using self-assembly. And in doing so we have created a whole range of new colloid or nanocomposite particles that we are now interested in using to self-assemble into other structures to fabricate advanced materials.

The effects of reducing materials to the nanoscale

Let’s look a bit more closely at some of the concepts you have been referring to. For example, how do things behave differently at the nanometre scale?

An example related to my group’s area of research would be metals. Many people would be familiar with the fact that a gold metal film can be reflective and has a yellowish appearance. If you have the same material sized down in the form of particles in the nanometre range, these particles exist, for example, in an aqueous solution and they can be red in colour. So they have totally different optical properties – on one hand you have a yellowish reflective coating; on the other hand, in the nanoregime, it is a colloidal dispersion, which to the eye appears red. That is an example of extreme differences that arise. And there are many analogous examples of differences in optical properties, in electronic properties, in magnetic properties and others, simply as a result of going down in size for these and other materials.

So a lot of nanotechnology is about trying to work out and exploit the properties of the substance when you take it from its bulk form and reduce it to nanometre-size particles?

Yes. That’s precisely what is interesting in nanotechnology, that material at the nanoscale level behaves very differently from similar material which is not at that scale. And one can utilise those properties to create advanced systems, structures, materials, for various applications.

Manipulating nanoparticles and nanosystems

How do you manipulate objects at the nanometre scale?

This is very challenging. A variety of techniques are used. Some involve state-of-the-art instruments – specifically-designed microscopes and others – but self-assembly, under controlled conditions, can also be used to manipulate some of these materials.

Self-assembly is essentially the ability for compounds or species, or materials for that matter, to assemble by themselves into various structures. Nature is full of examples of self-assembly, for example coral, a whole range of different materials. Self-assembly is very important because it enables us, in many instances, to prepare structures that otherwise we would not be able to. New avenues and methods are becoming available now to manipulate nanoscale systems in order to form advanced structures, but self-assembly provides a flexible and viable approach to creating structures by taking these nanoparticles or nanosystems and allowing them to assemble, on their own, into a desired final material or product.

So, for example, if you take a surface and pattern it with various functionalities, then you can assemble some of these nanocomponents onto certain areas on that surface. You can use pre-formed surfaces or you can use specially designed mechanical manipulators, but it is extremely challenging. This is where I believe there are going to be significant advances in the near future.

In our research we manipulate the materials through controlled assembly, in essence modifying the properties of the colloidal dispersions, through salt and pH – acidity, basicity of the solution – and that enables the dispersions to behave differently.

Possibilities presented by colloid particles

So what are colloids, and why is it important to be able to modify their surface properties?

Colloids are particles dispersed in a different phase, and they are present all around us, for example in milk, paints and also fog. The simplest case, of particles dispersed in water, is known as a colloidal dispersion. And if you would like to administer drugs to a body, for example, you can have colloidal drug delivery systems. If you can nanoengineer particles – that is, introduce new properties, new functions to those particles – you can manipulate those particles in terms of how much drug can be loaded and how the drug can be released in various applications. That then should have immediate translation to medicine in the area of drug delivery. That simple example is a very important one, as there is immense scope for improvement, just in being able to modify and control particles in solution.

Are you talking about loading the drug into these colloid particles?

Yes. There is a variety of colloids that one can make or modify. Some of these can be solid colloid particles, or they can be hollow. In the case that they are solid, one can imbed the drug within the particle; in the case that they are hollow, one can infill the particle with the drug. So you can infill or you can imbed in a different matrix or material, and then release those under certain conditions.

Focus questions

• Caruso mentions techniques that are used to manipulate objects at the nanometre scale. What are they and which technique does he use?

• How does Caruso explain the term colloid? What examples of colloids does he give?