Toward a Label-Free Electrochemical Impedance Immunosensor Design for Quantifying Cortisol in Tears.

Area of Science:

• Biomedical Engineering
• Analytical Chemistry
• Biochemistry

Background:

• Cortisol is a key biomarker for physiological, occupational, and emotional stress.
• Elevated cortisol levels are often present in tear fluid during stressful conditions.
• Current methods for cortisol detection can be time-consuming or require specialized equipment.

Purpose of the Study:

• To develop and characterize electrochemical methods for cortisol quantification in tear fluid.
• To design a disposable, handheld sensor for rapid, label-free cortisol detection.
• To compare the performance of electrochemical methods with the standard enzyme-linked immunosorbent assay (ELISA).

Main Methods:

• Electrochemical characterization of cortisol using cyclic voltammetry, amperometric i-t, and square wave voltammetry.
• Development of a label-free electrochemical impedance spectroscopy (EIS) based sensor.
• Prototyping of a disposable test strip and handheld sensor for tear fluid analysis.
• Comparison of sensor performance against ELISA for cortisol quantification.

Main Results:

• Cyclic voltammetry, amperometric i-t, and square wave voltammetry showed insufficient sensitivity for physiological cortisol ranges.
• Electrochemical impedance spectroscopy (EIS) demonstrated a viable method for cortisol quantification, with a detection range comparable to ELISA (~138 pM - 552 nM).
• The developed EIS biosensor achieved a lower limit of detection of 59.76 nM with approximately 10% relative standard deviation.

Conclusions:

• Electrochemical impedance spectroscopy (EIS) is a promising technique for sensitive and rapid cortisol detection in tear fluid.
• The prototyped disposable sensor offers a reproducible, label-free, and fast method for stress monitoring.
• This technology has the potential to significantly improve the accessibility and efficiency of stress biomarker analysis.