Antibody-Free Electrochemical Detection of Cortisol Using Molecularly Imprinted Polymer

Cortisol, an important steroid hormone in the body plays a key role in several stress related diseases including post-traumatic stress disorder [1-2]. Its continuous detection at room temperature still remains a challenge for providing timely health care to patients suffering from such diseases. We report here a novel, highly sensitive, and selective electrochemical cortisol sensor using molecularly imprinted polymer (MIP). MIP are synthetic polymers having highly specific recognition sites selective towards the target analyte and considered to be the versatile, stable and cost-effective alternatives for the natural antibodies. The cortisol specific MIP film was prepared by in situ electropolymerization of pyrrole [3] monomer onto the electrode surface in the presence of cortisol as a template. After removing the cortisol by electrochemical over-oxidation, the specific imprinted sites created on the polymer matrix were used to detect cortisol using ferrocyanide/ferricyanide (K₃[Fe(CN)₆]/K₄[Fe(CN)₆]) as a redox mediator. The imprinted sites on the electrode were characterized by cyclic voltammetry and scanning electron microscopy. The effect of experimental variables on the current response such as, electro-polymerization cycles, template/monomer ratio, elution condition for target removal, pH of the supporting electrolyte, and rebinding time were also investigated and optimized. The MIP based cortisol sensor exhibited a good detection limit of 1 pM mL^-1cortisol. Moreover, the sensor showed a good reusability, i.e., the sensitivity remained >90% after 6 cycles of elution/rebinding, while the sensitivity only decreased to 90% after 4 weeks of storage at room temperature.  Simplicity in preparation, high affinity towards cortisol, and stability superior to antibodies makes the MIP technology, a potential candidate for commercializing the cortisol sensor for point-of-care diagnosis.

References:

[1]   Rachel Yehuda, Sarah L Halligan, Robert Grossman, Childhood trauma and risk for PTSD: Relationship to intergenerational effects of trauma, parental PTSD, and cortisol excretion. Development and Psychopathology 13 (2001) 733–753.

[2]   Syed Khalid Pasha, Ajeet Kaushik, Abhay Vasudev, Shedra Amy Snipes, Shekhar Bhansali, Electrochemical Immunosensing of Saliva Cortisol, Journal of Electrochemial Society 161 (2014) B3077–B3032.

[3]   Manickam Pandiaraj, Niroj Kumar Sethy, Kalpana Bhargava, Vepa Kameswararao, Chandran Karunakaran, Designing label-free electrochemical immunosensors for cytochrome c using nanocomposites functionalized screen printed electrodes, Biosensors and Bioelectronics 54 (2014) 115–121.