A Prasanna de Silva tells Nicola Wise about sensors, supramolecular chemistry and how Sri Lankan percussion can play a part in Irish music

	A Prasanna de Silva is a professor at Queen's University Belfast, UK. His research interests include fluorescent sensors, molecule-based logic and molecular switches. He was awarded the RSC Award for Sensors in 2008 for his contribution towards 'switch and tell' sensor molecules and the invention of molecular logic.

 

Who or what inspired you to become a chemist?
Appreciating the value of teaching and learning was a gift from my paternal grandfather. Chemistry itself came to the fore at school under the influence of an exceptional teacher, Errol Fernando. These feelings about chemistry were reinforced in the University of Colombo, Sri Lanka, by Vincent Arkley and R S Ramakrishna. The usefulness of chemistry in real life situations was another reason I ended up as a chemist.

What led you to specialise in supramolecular chemistry?
The philosophical breadth of supramolecular chemistry, especially in the hands of Jean-Marie Lehn and Seiji Shinkai, was clear to see during the early 1980s. Around this time, I had just completed my PhD research in organic photochemistry at Queen's University Belfast under Jim Grimshaw. It was a pleasure to apply photochemical principles to the field of fluorescence analysis. Combining photochemistry with supramolecular chemistry permitted the fluorescence signalling of alkali metal ions - a virgin field at the time. However, my labours in supramolecular photochemistry would probably have ground to a halt if Ron Grigg had not given me the chance - out of the blue - to continue my research at Queen's University.

Your research helped develop blood diagnostic cassettes. How does this chemistry work?
Fluorescent molecular sensors can gather information about atomic or molecular behaviour from environments of nanometre dimensions. We developed sensors which contain a fluorescent unit and a receptor unit joined through a spacer module. This supermolecule loses its fluorescence capability owing to an inter-module photoinduced electron transfer (PET) quite similar to that seen in green plant photosynthesis. This PET process is stopped the moment the receptor module captures its target, for example a sodium ion, thereby switching the suppressed fluorescence back on. Thus, the fluorescence signal measures the concentration level of the target species.

In collaboration with Roche Diagnostics (now Optimedical), we produced fluorescent PET sensors held inside small plastic cassettes. These sensors respond to various blood gases and electrolytes and are used in hospital critical care units, ambulances, general practice surgeries and even veterinary environments. They serve as a wonderful example of supramolecular chemistry serving in real life situations around the world. The cassettes have had sales of over 55 million US dollars so far.

You have said in the past that you persuade molecules to perform arithmetic operations. What you mean by this?

While at the University of Colombo, I had the good fortune to be introduced to the fundamentals of digital electronics by Satish Namasivayam. Thus, it was lovely when Colin McCoy, Nimal Gunaratne and I were able to apply the idea of fluorescent PET sensors to develop molecular logic gates, launching the field of molecular logic and computation as an experimental science. Conventional silicon-based logic devices use electric voltages as the inputs and outputs. The first examples of molecular logic gates used chemical species such as protons and sodium ions as inputs along with fluorescence as the output. Nathan McClenaghan and I designed molecules which could perform the computation of adding one and one to get two. Though elementary, this computation is understandable to virtually everyone on the planet. So, persuading molecules to do arithmetic was an important early step on the journey of molecular logic and computation.

What achievement are you most proud of so far in your career?
It has been wonderful to establish the generality of the fluorescent PET sensor-switch system. The chance to start molecular logic and computation as an experimental science was another happy occasion. I am also very proud of my friendships with people from various parts of the world through science.

What is the next big thing that you would like to tackle in your lab?

Molecular logic and computation is a young field with a need to prove itself in different ways. Demonstrating real life applications that conventional silicon-based computing cannot do would be one such avenue. We have already shown an application where a population of small micrometric objects are given identification tags made up of molecular logic gates. This is a bit like faces on people or number plates on cars except everything is a lot smaller. Such molecular computational identification (MCID) can address far smaller objects than those handled conveniently by the popular radiofrequency identification technology. We now need to generalize this MCID technique and broaden its applicability. We are also trying to simplify molecular logic gate construction. Until now, each molecular logic gate had to be constructed via synthesis. Now we are arranging conditions so that molecular logic gates can be self-assembled from components that are simply mixed.

What is hot at the moment in your research area?
Molecular computing or data processing in small spaces is the hot topic. These molecular devices will reach where silicon devices cannot easily go, whether it be inside living cells, on the surface of plastic beads or inside detergent micelles.

If you had one piece of advice to pass on to young scientists, what would it be?
Chat with, and learn from, people practising other disciplines. It is a real tonic and you never know when cross-fertilisation will occur.

Which scientist, current or historic, do you most admire and why?
This is perhaps the toughest question to answer since there are many who are worthy of the utmost admiration. Thomas Andrews was the first professor of chemistry at the then Queen's College of Belfast 150 years ago. Every time water turns to vapour or ice, I am reminded of this man's work on the effects of temperature and pressure on materials. Also at that time, George Boole at University College Cork, Ireland, laid the foundations of modern computing with his ideas on logic and algebra. These two giants in the north and the south of a small island changed the way the world worked.

If you weren't a scientist, what would you do?
I would have to be a percussionist. I have played all my life and, like many Sri Lankan kids, I got my grounding in rhythm at a young age. Northern Ireland, with its rich musical tradition, is a great place to put that rhythm to use. It was a just matter of time before I was introduced to a band where a Sri Lankan percussionist could blend with Irish fiddles, flutes, banjos, bodhrans and voices. We have enjoyed playing together for the last 13 years, even though I have been advised to hold on to my day job!