The first electronic nose that can detect chiral compounds
In chemistry, molecules that can’t be superimposed onto their mirror image are said to be ‘chiral’. Each mirror image is called an enantiomer and when both are presented, the molecule is called a stereoisomer. While chiral molecules are considered the main building blocks of living organisms, each enantiomer can interact differently with living organisms – one can be beneficial, with the other toxic. This is important because chiral molecules are increasingly used in the manufacturing of food, pharmaceuticals, perfumes, cosmetics and agrochemicals. “25 % of all pesticides are made from chiral compounds with enantiomers that behave significantly differently from each other. This unpredictable impact on biological systems makes chiral pollutants a growing environmental problem,” says project coordinator Roberto Paolesse from Tor Vergata University of Rome, the project host. As standard analysis of these pesticide compounds usually doesn’t consider chirality, the INITIO project developed chemical sensors able to do so. Crucially, unlike currently available techniques, reliant on laboratory screening, INITIO’s innovation can do so in real time and in situ.
Chemical sensors
INITIO was prompted by the need of agricultural SMEs for devices able to effectively monitor pesticides in the field. The resultant device benefited from combined know-how from the world of chemical sensor development. Chemical sensors combine two principal components: the receptor (sensing material) and the signal transducer (an electronic component). When the receptor interacts with the target, its properties are changed which the transducer records and translates into a readable signal. However, single sensors are not ideal for detecting chirality because rather than ideally producing a signal for only one of the enantiomers, they usually produce a signal for both, making it impossible to differentiate them. To get around this, INITIO created a sensor array with only weak selectivity for enantiomers, mimicking natural olfaction. “To the best of our knowledge, this is the first ‘enantioselective electronic nose’ for the recognition of both different substances and their chiral nature,” adds Paolesse.
Testing times
Various receptors were characterised and then tested with different transducers to find those best able to discriminate between enantiomeric pairs. To achieve this, the team combined chiral inorganic structures, such as chiral nano-helices, with organic receptors, such as porphyrins or hemicucurbiturils. Additionally, a simpler approach was developed to produce chiral layers using supramolecular methods, where chiral receptors spontaneously assemble with non-chiral receptors, producing solid films able to recognise the different enantiomers of target analytes. The sensor array itself, based on quartz crystal microbalances, was tested for chiral discrimination in gas. “We improved the current version of the electronic nose developed at Tor Vergata University of Rome, providing up to 12 integrated sensors, a microfluidic system for sample delivery, an electronic board for data acquisition and updated algorithm-driven software able to recognise the chiral identity of compounds. Our sensor array successfully discriminated between model analytes from different classes of chiral compounds in lab conditions,” explains Paolesse.
Field monitoring for environmental control
Chiral pollutants are a growing ecological concern, as is evidenced by organochlorine pesticide pollution in the Baltic Sea. INITIO’s chiral discrimination and analysis tool offers a means to monitor their interaction with the environment for accurate risk assessments. According to Paolesse, the next step will be to demonstrate the device’s performance in the field with a wide range of analytes and for enantiomeric pairs in liquid, opening up the possibility of monitoring aquatic environments.
Keywords
INITIO, chiral compound, chemistry, enantiomer, pollutant, sensors, agricultural, pesticides
