ORIGINAL PAPER A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay Maliwan Amatatongchai & Oliver Hofmann & Duangjai Nacapricha & Orawon Chailapakul & Andrew J. deMello Received: 1 September 2006 / Revised: 9 October 2006 / Accepted: 11 October 2006 / Published online: 28 November 2006 # Springer-Verlag 2006 Abstract A microfluidic system incorporating chemilumi- nescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxy- oxalate chemiluminescence (PO-CL) assay with 9,10-bis- (phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchan- nels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA HP of 3.27× 10 -3 μmol -1 L), followed by α-tocopherol (SA HP of 2.36× 10 -3 μmol -1 L) and quercetin (SA HP of 0.31×10 -3 μmol -1 L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements. Keywords Antioxidant capacity . Peroxyoxalate chemiluminescence . Microfluidics Introduction In response to both external and internal stimuli, small amounts of reactive oxygen species (ROS) are constantly generated within aerobic organisms. These ROS species include hydrogen peroxide (H 2 O 2 ) and the hydroxyl (HO • ) and superoxide O  2 À Á radicals. In healthy individuals production of ROS is balanced by the antioxidative defence system. In situations in which there is a serious imbalance between production of ROS and antioxidative defence, cell injury occurs. This situation is normally defined as “oxidative stress” which results in damage to DNA, proteins, lipids, and uric acid. Oxidative stress is often found in patients suffering from chronic conditions such as Alzheimer’ s and Parkinson’ s disease. Damage caused by the action of free radicals may, moreover, initiate and promote the progression of several chronic diseases, for example cancer, cardiovascular disease, and inflammation [1]. Under conditions of oxidative stress, production of the free radicals is favoured, which results in reduction of antioxidant levels. The benefit of dietary intake of antioxidant compounds, either as food additives or as pharmaceutical supplements, in protecting the body against oxidative stress has been Anal Bioanal Chem (2007) 387:277–285 DOI 10.1007/s00216-006-0930-3 M. Amatatongchai : D. Nacapricha Department of Chemistry, Faculty of Science, Mahidol University, 10400 Bangkok, Thailand M. Amatatongchai Department of Chemistry, Faculty of Science, Ubonrajathanee University, 34190 Ubonratchathani, Thailand O. Hofmann BioIncubator Unit, Bessemer Building (RSM) Level 1, Prince Consort Road, London SW7 2BP, UK O. Chailapakul Department of Chemistry, Faculty of Science, Chulalongkorn University, 10330 Bangkok, Thailand A. J. deMello (*) Department of Chemistry, Imperial College London, London SW7 2AZ, UK e-mail: a.demello@imperial.ac.uk