An ultrasensitive dual optical method for measuring antioxidant concentration and total antioxidant capacity is provided. Using the process, the detection limit for vitamin C is as low as 7 nM. The method is based on a hybrid of single walled carbon nanotubes (SWNT) with hydrogen-peroxide. The method provides is a robust, cheap, fast, and reusable optical sensing method for antioxidant and total antioxidant capacity measurement in foods and plasma. The method can also be developed as a miniature assay for both in vitro and in vivo detection.