Hypochlorous acid (HOCl),a key ROS derivative produced by the neutrophil-derived enzyme myeloperoxidase at sites of inflammation,plays a central role in the antimicrobial action,and also implicates in several host tissue injury when accumulated excessively[1].Moreover,owing to the widespread endogenous antioxidant defense system[2],HOCl-mediated oxidation occurs at specific localized site in a dose constrained manner rather than widely distributed in bulk solution.Therefore,assessment of the scavenging capacity under physiological condition,especially by using controlled microassay that mimics quick,scope-limited HOCl scavenging reaction in vivo,is still needed to be developed.Here,a microfluidic chemiluminescence system (Fig.1) has been developed for assay of various endogenous antioxidants scavenging capacity against HOCl under physiologicallyrelevant conditions (1 μL of 50 μmol L-1 HOCl scavenged at physiological pH 7.4 saline media).Meanwhile,the rate of HOCl generation and oxidization is estimated physiologically at the level of 10 pmol/s,the scavenging reaction was controlled in the time frame of several seconds.On the basis of system optimization,the scavenging capacities of various endogenous antioxidants had been comparatively assessed.The CL inhibition percentage (IC50),were compared with those obtained by using DPD colorimetric method,and with the antioxidant level existed in human plasma (Table 1).Except a few hormones or their precursors,almost all endogenous antioxidants showed enough scavenging capacities.For most small molecule scavengers,the IC50 values were at the level of several micromolar which was one magnitude lower than those obtained from DPD method.But large proteinic antioxidant showed much stronger capacity,especially those thio-containing proteinic antioxidants with ultrahigh concentration (serum albumin) or ultrastrong scavenging capacity (SOD & catalase),played a significant role in scavenging HOCl in vivo.This developed method is sensitive,automatic with a high throughput (80 h-1) and a good precision (<1.5% RSD).When it was further applied for the assessment of scavenging capacity of practical blood samples,the assay result indicated that the serums scavenging capacities (Fig.2) show somehow correlation with neutrophilia and/or inflammation diseases,fostering our the application to screening analysis of HOCl scavenging capacity and supplementary diagnosis of HOCl-mediated diseases.