Teamwork at the Nanoscale

Nanoparticles are programmed microscopic particles that can respond to external stimuli such as light to perform functions, such as moving towards a chemical target or light source. The hope is that they can be harnessed for energy saving, drug delivery and other purposes. But they have a limitation: they are typically programmed as individual actors. Put a vast amount of them in a solution and their behaviour becomes unpredictable.

Dr Tang Jinyao has addressed this problem by treating nanorobots as a group rather than individuals. This follows on from his 2016 achievement developing the world’s first light-seeking synthetic nanorobot, which is about the size of a blood cell and is propelled by light through photochemical reactions.

A lot of hope was pinned to that discovery and its potential to deliver drugs and treatments for healthcare. But Dr Tang and his team found the individual nanoparticles were too small to be programmed for complex actions.

“However, we started to realise they could actually be a community. Like individual ants or bees in nature, they do not do much on their own. But as a group, they start to perform very smart functions. Materials science takes the same approach. We treat matter as a group of molecules or atoms and try to figure out the properties. In this case, we started to look at how our particles or nanorobots interacted with each other to see if some kind of intelligence or functions could emerge,” he said.

Like oil in water

Further studies showed that when a large number of light-seeking nanorobots were placed in a solution, the nanorobots behaved as a random mixture. But when different organic dye molecules were attached to the nanorobots, either red, blue or yellow, and a red light was shone on the solution, the red nanorobots absorbed the light and interacted with each other to dye the solution red – “like oil molecules in water attracting each other,” he said.

To Dr Tang this offered a new insight – that collectively, nanoparticles are like a material rather than individual units. Moreover, he showed they are active particles, not dead inert matter which is what most materials are made of. “This is basically the first example of how we can use active things for material applications. It is just one example and I expect more will emerge,” he said.

Possible applications could be using the nanoparticles to create electronic ink that reflects colour (similar to a Kindle, which only displays black and white) or produce camouflage or colour-shifting materials, such as a shirt that turns white under sunlight and black in the dark, or a building that changes colour to absorb sunlight when it is cold and repel it in the heat.

He noted that while this was not intelligence per se, he also showed in other circumstances that a simple group ‘intelligence’ can emerge when programmed nanoparticles work together to make decisions in a complicated environment. That work is supported by a Croucher Senior Research Fellowship.

Following the leader

The basic interaction still involves nanoparticles attracting or repelling each other but they are programmed to follow each other’s lead. Each particle can only sense its local environment, but when there are a lot of them, they propagate information through their interaction chains and come to a consensus on which direction to go in.

An example of how this might work beyond the experimental lab is with cancerous tumours, which give off weak signals. The nanoparticles ostensibly could be programmed to sense the signal, with those closest to the tumour sensing the tumour first. They would move towards the tumour, attracting other particles, which would build up to a consensus for all other particles to follow. However, Dr Tang cautioned that tumour targeting is still only an aspiration and more work is needed.

“Other researchers have not really realised the importance of the interaction between different particles, so we want to at least develop several theories or protocols on programming these groups,” he said. “One way of doing that is to study them as a material because there are techniques in materials science that we could apply. And of course, we want to develop new techniques.”

Dr Tang noted that communication between nanoparticles was what linked his two lines of study. He hopes in future to uncover other properties of active matters and intelligent matters and find useful applications, though these will not likely be in the biomedical field at this stage given the regulations and complexities involved. “There’s no product yet but we want to make the first one. Hopefully, others will follow and there will be more investment in this research,” he said.