Biosensing of tuberculosis volatile biomarkers using insect odorant receptors

Current diagnostics for tuberculosis (TB) are slow, expensive, and often reliant on highly trained personnel which limit their use, especially in areas with the highest disease burden. Recent studies have identified that volatile organic compound (VOC) biomarkers for TB diagnosis exist in breath, skin and urine samples, opening the door to the rapid non-invasive diagnosis of TB patients. Unfortunately, current VOC sensing approaches are not available in a portable format for infield real-time diagnosis of TB patients. Here we present an insect Odorant Receptor (OR) based biosensing approach for the detection of TB biomarker VOCs. We validate this approach using three Drosophila melanogaster odorant receptors: DmOr42a and DmOr69a for the breath TB biomarkers 2-butanone and nonanal, respectively, and DmOr35a for the skin TB biomarker hexyl butyrate. We overexpress, purify and reconstitute each receptor with DmOrco into liposomes. We then use fuse each DmOrX/Orco liposome with planar lipid bilayers to enable ion channel measurements. By directly monitoring the change in electrical current through the planar lipid bilayer we can detect binding of each biomarker VOC to their respective receptor. Furthermore, we show with DmOr69a/Orco that it is possible to detect a VOC biomarker at the nM (ppB) concentration, providing the sensitivity required for disease diagnosis in biological samples. This study is the first step towards the development of an OR based electrochemical biosensor for the rapid point-of-care diagnosis of TB and other disease states which have unique volatile signatures.