Tokyo Tech researchers recently demonstrated graphene-based olfactory sensors that can detect odor molecules based on patterned peptide sequences. The findings indicated that graphene field effect transistors (GFETs) functionalized with designable peptides can be used to develop electronic devices that mimic olfactory receptors and emulate the sense of smell by selectively sensing odor molecules.
Olfactory detection or odor detection is an integral part of many industries, including healthcare, food, cosmetics, and environmental monitoring. Currently, the most widely used technique for the detection and estimation of odor molecules is gas chromatography-mass spectrometry (GC-MS). Although very effective, GC-MS has some limitations, such as its bulky setup and limited sensitivity. As a consequence, scientists have been looking for more sensitive and easy-to-use alternatives.
In recent years, graphene field effect transistors (GFETs) have started to be used to develop highly sensitive and selective odor sensors by integrating 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 GFETs as electrical biosensors with the receptors is severely limited by factors such as the fragility of the receptors and the lack of highly native synthetic molecules that can function as olfactory receptors.
A team of researchers at the Tokyo Institute of Technology (Tokyo Tech) led by Prof. Yuhei Hayamizu set out to address these issues with GFET-based olfactory receptors. In his recent study published in Biosensors and Bioelectronics, The team designed and developed three new peptides for graphene biosensors that can detect odor molecules. Prof. Hayamizu explains: “The peptide sequence we designed needed to perform two main functions: to act as a biomolecular scaffold for self-assembly on a graphene surface, and to function as a bioprobe to bind odor molecules. This would allow the peptides to cover the graphene surface in a self-assembled manner and functionalize the surface evenly to capture odor molecules.”
The team carried out atomic force microscopy which showed that the peptides evenly covered the graphene surface with the thickness of a single molecule. The functionalized graphene was then used to build a GFET setup to detect odor molecules. After assembly, the team injected limonene, menthol, and methyl salicylate as representative odorant molecules into the GFET. Electrochemical measurements indicated that the binding with the odorant molecules reduced the conductivity of the graphene. The observations also revealed that the interaction between the three peptide sequences and the odor molecule gave rise to very different signatures. This confirmed that the GFET response to odor molecules was dependent on peptide design.
In addition, the team carried out electrical measurements in real time to monitor the kinetic response of the GFET. Observations indicated that the time constraint associated with the adsorption and desorption of odorant molecules was unique for each of the peptide sequences. This behavior was confirmed by principal component analysis. These observations confirmed that the new GFET setup succeeded in electrically detecting the odorant molecules with the help of the engineered 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 making the concept of electronic noses,” he says. Professor Hayamizu.
The robust approach presented in this study opens new doors for the development of highly selective and sensitive GFET-based odor detection systems. These insights can also be used when designing advanced peptide sensors that can perform multidimensional analysis of a range of odor molecules.