Detection of a secreted protein biomarker for citrus Huanglongbing using a single-walled carbon nanotubes-based chemiresistive biosensor

Citrus greening, or Huanglongbing (HLB), is currently the most devasting disease of citrus, creating unprecedented crisis for the multibillion-dollar global citrus industry. To-date, there is no effective cure and disease management relies on early detection and removal of infected trees. Thus, it is imperative that accurate, timely, and robust disease detection and diagnosis technologies are available to minimize the spread of disease. This study reports a sensitive and selective label-free biosensor that combines the physical and chemical advantages of carbon nanomaterials like single-walled carbon nanotubes (SWNTs) in a field-effect transistor (FET)/chemiresistor architecture with selective antibodies against Sec-delivered effector 1 (SDE1), a secreted protein biomarker, for the detection of HLB. The biosensor detected SDE1 biomarkers for citrus greening in plant tissue extracts with the dynamic range over three orders of magnitude in the low nanomolar to micromolar concentration range and limit of detection of 5 nM. The study also demonstrated the use of the standard additions assay method with the biosensor to attain a 90-percent signal recovery in concentrated plant tissue extract, allowing for quantitative detection without an external calibration. Adopting the novel detection strategy targeting the secreted protein biomarker, SDE1, addresses some of the challenges faced by current methods of nucleic acid-based assays and symptom-based diagnosis, which have been found prone to false negatives and mis-diagnoses, respectively.