Label-free, chemiresistor immunosensor for stress biomarker cortisol in saliva

Biosens Bioelectron. 2011 Jul 15;26(11):4382-6. doi: 10.1016/j.bios.2011.04.045. Epub 2011 May 31.


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.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Biomarkers / analysis
  • Biosensing Techniques / methods*
  • Humans
  • Hydrocortisone / analysis*
  • Hypothalamo-Hypophyseal System / physiology
  • Nanotechnology
  • Nanotubes, Carbon
  • Pituitary-Adrenal System / physiology
  • Saliva / chemistry*
  • Stress, Physiological / physiology


  • Biomarkers
  • Nanotubes, Carbon
  • Hydrocortisone