Electrochemical cortisol immunosensors based on sonochemically synthesized zinc oxide 1D nanorods and 2D nanoflakes

Biosens Bioelectron. 2015 Jan 15;63:124-130. doi: 10.1016/j.bios.2014.07.026. Epub 2014 Jul 17.


We report on label free, highly sensitive and selective electrochemical immunosensors based on one-dimensional 1D ZnO nanorods (ZnO-NRs) and two-dimensional 2D ZnO nanoflakes (ZnO-NFs) which were synthesized on Au-coated substrates using simple one step sonochemical approach. Selective detection of cortisol using cyclic voltammetry (CV) is achieved by immobilizing anti-cortisol antibody (Anti-C(ab)) on the ZnO nanostructures (NSs). 1D ZnO-NRs and 2D ZnO-NFs provide unique sensing advantages over bulk materials. While 1D-NSs boast a high surface area to volume ratio, 2D-NSs with large area in polarized (0001) plane and high surface charge density could promote higher Anti-C(ab) loading and thus better sensing performance. Beside large surface area, ZnO-NSs also exhibit higher chemical stability, high catalytic activity, and biocompatibility. TEM studies showed that both ZnO-NSs are single crystalline oriented in (0001) plane. The measured sensing parameters are in the physiological range with a sensitivity of 11.86 µA/M exhibited by ZnO-NRs and 7.74 µA/M by ZnO-NFs with the lowest detection limit of 1 pM which is 100 times better than conventional enzyme-linked immunosorbant immunoassay (ELISA). ZnO-NSs based cortisol immunosensors were tested on human saliva samples and the performance were validated with conventional (ELISA) method which exhibits a remarkable correlation. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring/diagnostic.

Keywords: Cortisol sensing; Immunosensor; Sonochemistry; ZnO nanoflakes; ZnO nanorods.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Biosensing Techniques / methods*
  • Gold / chemistry
  • Humans
  • Hydrocortisone / chemistry
  • Hydrocortisone / isolation & purification*
  • Limit of Detection
  • Nanostructures
  • Nanotubes / chemistry*
  • Zinc Oxide / chemistry*


  • Gold
  • Zinc Oxide
  • Hydrocortisone