Researchers at Tokyo Tech have demonstrated graphene-based olfactory sensors that can detect odor molecules based on peptide sequence design. The results showed that graphene field-effect transistors (GFETs) functionalized with designed peptides can be used to develop electronic devices that mimic olfactory receptors and mimic the sense of smell by selectively detecting odor molecules.
Olfactory sensing or smell detection is an integral part of many industries including healthcare, food, cosmetics and environmental monitoring. Currently, the most commonly used technique for the detection and evaluation of odor molecules is gas chromatography-mass spectrometry (GC-MS). Although very efficient, GC-MS has certain limitations, such as its large bulky setup and limited sensitivity. As a result, scientists are looking for alternatives that are more sensitive and easier to use.
In recent years, graphene field-effect transistors (GFETs) have begun to be used to develop highly sensitive and selective odor sensors through integration with olfactory receptors, also known as electronic noses. The atomically flat surfaces and high electron mobility of graphene surfaces make GFETs ideal for adsorbing odor molecules. However, the application of GFET as electrical biosensors with the receptors is greatly limited by factors, such as the fragility of the receptors and the lack of synthetic altenic molecules that can act as olfactory receptors.
A team of researchers from the Tokyo Institute of Technology (Tokyo Tech) led by Professor Yuhei Hayamizu set out to address these issues with GFET-based olfactory receptors. In a recent study published in Biosensors and Bioelectronics, the team designed and developed three new peptides for graphene biosensors that can detect odor molecules. Professor Hayamizu explains “The sequence of peptides we designed needed to fulfill two main functions – to act as a biomolecular scaffold for self-assembly on the surface of graphene and to act as a biotracer to attach the odorant molecules. This would allow the peptides to the surface to cover graphene in a self-assembling manner and uniformly functionalize the surface to trap odor molecules.”
The team performed atomic force microscopy which showed that the peptides uniformly covered the graphene surface with a thickness of one molecule. The functionalized graphene was then used to build a GFET setup to detect odor molecules. After assembly, the team inserted limonene, menthol, and methyl salicylate as representative odor molecules into the GFET. The electrochemical measurements showed that binding to the odorant molecules reduced the conductivity of the graphene. The observations also showed that the interaction between the three peptide sequences and the odorant molecule resulted in very different signatures. This confirmed that the response of the GFET to the odorant molecules was dependent on the peptide design.
In addition, the team performed real-time electrical measurements to monitor the kinetic response of the GFET. The observations indicated that the time limit of adsorption and desorption of odorant molecules was unique for each of the peptide sequences. This behavior was further confirmed by principal components analysis. These observations confirmed that the new GFET setup was successful in electrically detecting the odor molecules with the help of the designed peptides.
“Our approach is simple and can be scaled up for the mass production of peptide-based olfactory receptors that can mimic and miniaturize the natural protein receptors responsible for our sense of smell. We are one step closer to the realization of the concept of the electronic nose,” says Professor Hayamizu.
The robust approach presented in this study opens new doors for the development of highly selective and sensitive GFET-based odor sensing systems. These insights can also be used in the design of advanced peptide sensors that can perform multidimensional analysis of a range of odorant molecules.