Biosensing with Insect Odorant Receptor Nanodiscs and Carbon Nanotube Field-Effect Transistors

Abstract

Insect odorant receptors have been reconstituted into lipid nanodiscs and tethered to carbon nanotube field-effect transistors to function as a biosensor. Here, four different insect odorant receptors (ORs) from Drosophila melanogaster (DmelOR10a, DmelOR22a, DmelOR35a, and DmelOR71a) were expressed in Sf9 cells, purified, and reconstituted into lipid nanodiscs. We have demonstrated that each of these ORs produce a selective and highly sensitive electrical response to their respective positive ligands, methyl salicylate, methyl hexanoate, trans-2-hexen-1-al, and 4-ethylguaiacol, with limits of detection in the low femtomolar range. No detection was observed for each OR against control ligands, and empty nanodiscs showed no specific sensor signal for any of the odorant molecules. Our results are the first evidence that insect ORs can be integrated into lipid nanodiscs and used as primary sensing elements for bioelectronic nose technologies.

Putative ligand binding sites of two functionally characterized bark beetle odorant receptors

“…From an applied perspective, functional characterization of ORs and determination of their binding sites are pertinent in pest insects, because receptors that are key to survival and reproduction represent potential targets for improved pest control using OR antagonists and agonists 4 . Also, with the advancement of biosensor technology towards using ORs to detect insect semiochemicals [15][16][17] , employing receptors tuned to the characteristic odors of a pest, such as bark beetle aggregation pheromones, could be useful for early detection of infestations.…”

The Emergence of Insect Odorant Receptor-Based Biosensors

“…The nanodiscs were immobilized onto CNT-FET via physical adsorption and challenged with the cognate ligands: methyl salicylate, methyl hexanoate, trans-2-hexen-1-al, and 4-ethylguaiacol. Ligand concentrations of 1 fM were detected [48].…”

“…hOR, human odorant receptor; DmelOR, Drosophila melanogaster odorant receptor; MDL, minimum detection limit. Data cited from: Jin et al [35]; Goldsmith et al [36]; Yang et al [46]; Lee et al [47]; Murugathas et al [48]; Khadka et al [49]; Sung et al [50]; Lim et al [51]; Oh et al [52]; Park et al [53]; and Ahn et al [54].…”

“…The feasibility of CNT-FET biosensors was demonstrated in the detection of nucleic acids [98][99][100][101] and various protein biomarkers [102] and they are considered the next generation bioelectronic-based biosensors. Detection of VOCs with CNT-FET devices that were bio-functionalized with ORs for specificity is less common [48]. Human ORs were immobilized on a network of single-walled CNT in a FET configuration and the drain current was measured as a function of time.…”

Bio-Inspired Strategies for Improving the Selectivity and Sensitivity of Artificial Noses: A Review

“…First, their structure is essential for their binding function, and a lipidic environment is necessary to preserve it. Membrane fractions [20,21], then nanovesicles or nanoliposomes [22][23][24][25], and eventually nanodiscs ( Figure 2b) [15,26,27] have been used to achieve their immobilization on sensors. Second, the fact that they are not soluble makes their production challenging.…”