title: Label-free, chemiresistor immunosensor for stress biomarker cortisol in saliva.
abstract: Salivary cortisol is commonly used as a bioindicator of the psychobiologic response to environmental and psychological stressors. Current analytical approaches rely on immunoassays performed at distant, centralized laboratories and involve an elaborate specimen collection-processing-transportation-storage-analysis-reporting cycle. To facilitate point-of-use measurement of salivary cortisol levels, we describe the development and proof-of-concept testing of an ultrasensitive, label-free immunosensor based on a single-walled, carbon nanotube-based chemiresistive transducer. Carbon nanotubes were functionalized with a cortisol analog [cortisol-3-CMO-NHS ester] and a monoclonal anti-cortisol antibody was ligated to this receptor. Addition of phosphate buffer as well as artificial saliva spiked with varying cortisol concentrations displaced the anti-cortisol antibody producing corresponding decreases in the resistance/conductance of the nanotube-biomolecule hybrid. The immunosensor demonstrated an ultralow detection limit of 1 pg/ml and excellent binding selectivity for cortisol even in the presence of structurally similar steroids such as 21-hydroprogesterone. The nanotube immunosensor offers attractive prospects for the development of highly sensitive biosensor for rapid, label-free measurement of salivary cortisol in a variety of clinical and research settings.
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA.
authors.forename: Chaker
authors.initials: C
authors.lastname: Tlili
authors.forename: Nosang V
authors.initials: NV
authors.lastname: Myung
authors.forename: Vivek
authors.initials: V
authors.lastname: Shetty
authors.forename: Ashok
authors.initials: A
authors.lastname: Mulchandani
mesh_terms: D015415:Biomarkers / Q000032:analysis; D015374:Biosensing Techniques / Q000379:methods*; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D036103:Nanotechnology; D037742:Nanotubes, Carbon; D010913:Pituitary-Adrenal System / Q000502:physiology; D012463:Saliva / Q000737:chemistry*; D013312:Stress, Physiological / Q000502:physiology
chemical_list: D015415:Biomarkers; D037742:Nanotubes, Carbon; D006854:Hydrocortisone