Antioxidant activity evaluation of trace sample by the spot measurement of singlet oxygen luminescence lifetime

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In order to evaluate antioxidant activities of trace amount of natural materials, a method of measuring lifetimes of singlet oxygen near-infrared luminescence using a fiber-spot probe (0.4 mm) was developed. Time-evolutions of singlet oxygen luminescence were successfully obtained from measurements of less than 0.1 mL of solutions and also hydrogel samples by the spot method. The quenching rate constants for trace amount of samples such as 0.05 mg of carotenoid isomers, and also that of the quencher in hydro-gel samples were determined. The relationship between singlet oxygen quenching activity and chemical structure for the lipophilic constituents of spices such as capsaicin were investigated in the cyclodextrin aqueous solution. However, in the spot measurements, the photo-damages often occurred in test materials and/or photosensitizers in the accumulation time (10 min). The shorter accumulation time (< 1 min) is hopeful for applying the spot-scan method to the antioxidant assay.