Electronic nose for enantioselective odor detection of different volatile organic compounds (VOC)
Researchers at the Karlsruhe Institute of Technology (KIT) have developed novel sensor arrays ("electronic noses") that are able to detect and distinguish enantiomers of different volatile organic compounds (VOC) simultaneously and with high accuracy. Chirality and enantioselectivity are very important in nature and crucial in various fields. Many odor molecules are chiral and most chiral odor molecules have an enantioselective smell, meaning that the perception of enantiomers by the human nose differs significantly.
E-nose systems without enantioselectivity are established and are indeed used to detect odors, for example, to assess the authenticity and adulteration of food products. The active sensing materials in such conventional e-noses typically use polymers or inorganic materials with large surface areas as well as metal-organic frameworks. However, many more or less successful attempts have been made so far to fabricate enantioselective sensors. Various chiral materials based on chiral polymers, supramolecular chiral systems, carbon nanotubes or graphene functionalized with chiral molecules have been tested to distinguish the enantiomers of a chiral molecule in a single sensor assembly.
The overall market for e-noses was valued at USD 17.9 million in 2020. It is projected to grow at a remarkable CAGR of over 11 % in the next years with key markets also in Europe. The fastest growing market and the largest absolute market are assumed to be the US.
The range of applications of an enantioselective e-nose is diverse, ranging from sensing of bioactive chiral pheromones, e.g. to measure and inhibit communication between pest insects, via investigation of product piracy, e.g. of chiral perfumes and flavors, to quality control of foodstuffs. However, enantioselective discrimination is still only possible by combining a conventional e-nose with an enantioselective technique such as chiral chromatography or electrophoresis. That is time-consuming and costly.
Novel sensor arrays ("enantioselective e-noses") have been developed which are able to detect and distinguish enantiomers of different volatile organic compounds (VOC) simultaneously and with high accuracy. They are based on quartz-crystal microbalance (QCM) sensors coated with six different nanoporous homochiral and achiral metal-organic framework (MOF) thin films. By machine learning algorithms based on k-nearest-neighbor (kNN) analysis, the sensor array can distinguish all molecules and its isomers with more than 97 % confidence.
- Enantioselective detection of chiral molecules (VOC) and mixtures
- Combination of e-nose setup with various homochiral thin films of metal-organic frameworks (MOF)
- High accuracy
- High sensitivity
- Uses machine learning algorithms (k-nearest-neighbor, kNN) for stereoselective identification
Enantioselective e-noses are suitable for automated monitoring of chiral odor sources in contrast to olfactometry with human persons who can only perform random sampling. Multiple applications are possible, especially detection of product piracy, e.g. of chiral fragrances and flavors, and quality control of food like olive oil.
Find out more
Okur, Salih; Qin, Peng; Chandresh, Abhinav; Li, Chun; Zhang, Zejun; Lemmer, Ulrich; Heinke, Lars (2021):
"An Enantioselective e-Nose: An Array of Nanoporous Homochiral MOF Films for Stereospecific Sensing of Chiral Odors."
In: Angewandte Chemie (International ed. in English) 60 (7), S. 3566–3571. DOI: 10.1002/anie.202013227