Single-Walled Carbon Nanotube-Based Field-Effect Transistors Functionalized with Odorant Receptors for Biosensing Applications

Abstract

Bioelectronic detection with functionalized carbon nanotube transistor devices, known as CNT-FET, offers signal levels comparable with voltage clamp, multiplexing potential similar to microarray and amenability for miniaturization. The feasibility of CNT-FET biosensors was demonstrated in the detection of nucleic acids and various protein biomarkers and they are considered the next generation bioelectronic-based biosensors. Detection of volatiles and specifically volatile organic compounds (VOC) with CNT-FETs is less common, let alone devices that were biofunctionalized for specificity. The detection of VOCs has been demonstrated in a wide range of applications, with early reports focusing on environmental exogenous VOCs due to their adverse effects on human health; bacterial VOC signatures used as disease biomarkers, etc.. Methods that rely on separation techniques coupled with mass spectrometry are considered the ’gold standard’ in this field. These methods require expensive equipment, labor-intensive preparation steps and trained personnel, and are not suitable for field use. A method enabling high-throughput screening of VOCs such as insect behavior-modifying drugs, disease biomarkers, etc. is highly desirable.Bioelectronic sensors are ideally suited for the detection of pathogenic volatile markers (VOC). In order to confer ultrahigh specificity on an electronic sensor, a bio-recognition element needs to be incorporated with the transducer. In the case of VOC sensing, one such promising element is the natural insect odorant receptor (OR). Insect OR exhibit remarkable sensitivities and the ability to selectively detect a vast number of VOCs. These heteromeric transmembrane proteins transduce signals by acting as ligand-gated ion channels. We have recently developed OR-functionalized carbon nanotube field-effect transistor (FET) devices. These FET devices integrate an isolated single-walled carbon nanotube (SWCNT) as the conducting channel material.Indole and skatoles are microbial volatile organic compounds (VOCs). Depending on their concentrations, these odorants indicate environmental contaminants, metabolic disorders, food spoilage, human presence and malodorants.The indolergic receptor (IndolOR) named OR9 is the most sensitive odorant receptor discovered so far. We have developed a bioelectronic assay platform in the form of OR9-functionalized CNT-FET arrays. Our unique functionalization method is based on directing the attachment of a native OR9-containing nanovesicles (which we have exogenously expressed and functionally characterized) to the CNT-FET point defect. Target binding-induced ionic current and conformational changes of OR9 affect an electric field that modulates the device conductance. Figure 1