LAUSR

Abstract The activity of leukocyte esterase (LE) is a proxy for the presence of leukocytes in the diagnosis of infection, a common cause of patient morbidity and mortality. Here, the ability of commercial glucose test strips to detect hydroquinone (HQ) down to 1.0 μM was explored for the determination of LE in human synovial (joint) fluid and urine samples. To this end, the HQ-releasing substrate (HQS) for LE was synthesized and tested by chronocoulometry at a glucose strip linked to a laboratory potentiostat. The latter was used, rather than a glucometer, to improve the limit of detection. In the presence of LE in a sample, the HQS discharged HQ that was detected at a glucose strip covering a clinically relevant range from 20 μg L−1 (0.64 nM) to 750 μg L−1 LE (R2, 0.973, N = 8). Such a coulometric assay was selective with respect to human LE and required a 20-min sample incubation with HQS, which is much shorter than the current hours-long immunoassays for LE. The assay relied on a differential signal, which circumvented the interferences including those from endogenous glucose and provided a direct measure of infection regardless of the complexity of sample matrix. The scaled-up synthesis of HQS along with the wide availability of glucose strips provides a prospect for the commercialization of such an infection assay.