RESUMEN
Conventional competitive enzyme-linked immunosorbent assay (ELISA) to measure the cortisol level in body fluid consumes a large amount of time, owing to complicated operations involved and requirement for precise control of reagent addition. We developed an automatic microfluidic system to detect salivary cortisol rapidly, and an electrospun polystyrene (PS) microfiber-based reactor providing considerable binding sites for antibody immobilization, thus resolving the time limitations of competitive ELISA. Cortisol sample, horseradish peroxidase (HRP)-conjugated cortisol, and 3,3',5,5'-tetramethylbenzidine (TMB) substrate were delivered to the PS reactor from containers in sequence by pumps automatically. The color variation due to oxidized TMB complex reflects the cortisol concentration level measured using an RGB phototransistor. In addition, the entire procedure from sample introduction to obtaining the photocurrent took only 15 min. This system can be implemented to quantify cortisol from 0.37 ng/mL to 30 ng/mL, and the limit of detection was estimated at 0.37 ng/mL.