Scientists engineer 'Venus flytrap' bio-sensors to snare pollutants

Porphyrins, a unique class of intensely coloured pigments -- also known as the "pigments of life" -- provide the key to this ground-breaking innovation.

The word porphyrin is derived from the Greek word porphura, meaning purple, and the first chapter detailing the medical-chemical history of porphyrins goes back to the days of Herodotus (circa 484 to 425 BC). This tale has been progressing ever since and is at the heart of Professor Mathias O. Senge's work at Trinity.

In living organisms, porphyrins play an important role in metabolism, with the most prominent examples being heme (the red blood cell pigment responsible for transporting oxygen) and chlorophyll (the green plant pigment responsible for harvesting light and driving photosynthesis).

In nature, the active versions of these molecules contain a variety of metals in their core, which gives rise to a set of unique properties.

The researchers at Trinity, under the supervision of Professor Mathias O. Senge, Chair of Organic Chemistry, chose a disruptive approach of exploring the metal-free version of porphyrins. Their work has created an entirely new range of molecular receptors.

By forcing porphyrin molecules to turn inside out, into the shape of a saddle, they were able to exploit the formerly inaccessible core of the system. Then, by introducing functional groups near the active centre they were able to catch small molecules -- such as pharmaceutical or agricultural pollutants, for example pyrophosphates and sulphates -- and then hold them in the receptor-like cavity.

Porphyrins are colour-intense compounds so when a target molecule is captured this results in the colour changing drastically. This underlines the value of porphyrins as bio-sensors because it is clear when they have successfully captured their targets.

Karolis Norvaiša, an Irish Research Council-funded PhD Researcher at Trinity, and first author of the study, said:

"These sensors are like Venus flytraps. If you bend the molecules out of shape, they resemble the opening leaves of a Venus flytrap and, if you look inside, there are short stiff hairs that act as triggers. When anything interacts with these hairs, the two lobes of the leaves snap shut."

"The peripheral groups of the porphyrin then selectively hold suitable target molecules in place within its core, creating a functional and selective binding pocket, in exactly the same way as the finger-like projections of Venus flytraps keep unfortunate target insects inside."

The discovery was recently published in the print version of the leading international journal Angewandte Chemie International Edition and is featured as a hot paper. It has also been selected as the journal's cover illustration.

The work highlights the beginning of an EU-wide H2020 FET-OPEN project called INITIO, which aims to detect and remove pollutants. The work was made possible by initial funding from Science Foundation Ireland and an August-Wilhelm Scheer guest professorship award for Professor Senge at the Technical University of Munich.

Professor Senge added:

"Gaining an understanding of the porphyrin core's interactions is an important milestone for artificial porphyrin-based enzyme-like catalysts. We will slowly but surely get to the point where we can realise and utilise the full potential of porphyrin-substrate interfaces to remove pollutants, monitor the state of the environment, process security threats, and deliver medical diagnostics."