Sensitive New Age chemistry

 

Sometimes, a very small amount of something can have a big effect. Minute traces of contraceptive estrogen in waterways can affect fish, toxins from algal blooms can cause shellfish to become dangerous to eat, and bacteria in air conditioning can lead to Legionnaire’s disease.

A major issue has been finding a way to detect something that exists in such small quantities. Now, a team led by Associate Professor Ashton Partridge, Director of the IFS MacDiarmid Centre at Massey University, is using nanotechnology to develop sensors to detect these and many other elusive substances.

The team is using a technology called Surface Plasmon Resonance (SPR), which involves shining light on a gold/glass interface, causing a detectible high frequency oscillation of the gold. A specific antibody is attached to the gold surface, and if a solution is added that contains the substance of interest, it binds to the antibody, causing measurable changes in the oscillations. The method is extremely sensitive, able to detect substances in solutions that contain just a few thousand molecules.

“We use a MacDiarmid Institute-funded piece of apparatus called the SPR instrument. We bought this through the capital funding that was given out to develop the CoREs and that’s just great,” said Associate Professor Partridge. “The underlying mechanism is very straightforward, and is exactly the same for each different application. What we do is to make the sensors that go into it. We have to synthesise the different antibodies and antigens, and that can be rather difficult at times. But it’s do-able.”

Over the years, the team has come across many applications for the technology. For example, they have worked with the Massey University Veterinary School on facial eczema in calves, an important issue in New Zealand, and with ESR on detecting the toxins in algal blooms. Associate Professor Partridge has also carried out extensive work on olive oil, developing methods to detect whether a batch is virgin or extra virgin. Another use of the technology has involved testing for the bacteria that causes Legionnaire’s disease in air conditioning units.

The technology also has interesting potential for use in environmental monitoring. For example, in countries with high populations where many people take contraceptive pills, estrogen can make its way into waterways via the sewer system, affecting animals and fish. Having a test that can measure these very low levels of estrogen is very useful, and the team has made a sensor for this purpose.

In collaboration with Dr Yinqui Wu at HortResearch, the team has recently developed a way to increase the sensitivity of the technology even further, using gold nanoparticles. “Say I have a solution from the sea and I want to measure how much estrogen is in it,” explained Associate Professor Partridge, “I flow that across my sensor and watch it bind. Then, I flow estrogen that’s bound to a gold nanoparticle across it. If there’s no estrogen in the seawater solution then the estrogen attached to the gold nanoparticle will bind and give a known response. But if some of the antibody has been bound by estrogen from the seawater then less of the gold nanoparticle will bind than it would otherwise, and we can detect and measure this change.”

The group is now also working on transferring the chemistry they have developed into making ‘strip’ sensors for various applications. These are portable, disposable and very cheap, and use a similar technology to everyday pregnancy tests. “They’re nowhere near as sensitive, but we will just see how far we can go. There will be niche markets for this type of thing.”

Commercialisation is, in fact, a key driver for Associate Professor Partridge. “Everything I do has got a commercial slant. I can’t be bothered doing science for the sake of it because there’s so much fundamental work that can be done if you support commercial endeavours. We have such an opportunity here but we have no industry for the students that we teach to go to. I want to push commercialisation so that they have jobs to go to. That’s a major driver for me. I’ll never get rich out of it myself but I’ll have a lot of fun. I don’t need to get wealthy – although my wife would like me to!”

After years of dedicated work, the team is now at a stage where they have great confidence in the technology, and want to see how far it can go. “I believe in the technology. There’s a huge potential there. We’re at a stage of looking at what would be really useful to detect, and talking to various companies in New Zealand and overseas.”