Low-Cost Printed Point-of-Care Electrochemical Sensors for Detecting Cortisol

Screen printing system has been used as one of the important technologies for developing ready to use portable biosensor devices. Screen printing allows the batch production of sensors on flexible substrates, textile materials and other wearable accessories. Owing to an exceptional performance such as flexibility, low cost, simple fabrication, and ability to translated into industrial scale production, screen printing technique advances the marketing potential of the electrochemical sensors. Unlike the advanced printing techniques, the screen-printing technique is less dependent on surface charge, particle size and the viscosity of the printing ink. In this work, we have attempted to develop a flexible electrochemical sensor for detecting cortisol levels using screen printing technique. Batches of three electrode sensor systems were designed and printed in uniform dimensions (2 cm x 2 cm). The mask for sensor design is fabricated using a transparent polyester sheet with an aid of XY cutter/plotter. Graphene ink was used to create working and counter electrodes, while the Ag/AgCl ink was used to create the reference electrode. A homemade silver ink stabilized with hydrogel network was used to create conductive tracks. A reagent-free detection of cortisol was demonstrated using a redox probe (methylene blue) tagged cortisol specific aptamer immobilized onto the working electrode. The variability between the sensor batches is also investigated. The functionality of the printed sensor was demonstrated for monitoring cortisol levels in human saliva samples. The printed sensing platform can also be integrated with wearable textile platform for monitoring cortisol levels in sweat.