DOI: 10.1002/elan.201400576 Origin of Low Detection Limit and High Selectivity of Roche Accu-Chek Test Strips that Enables Measurement of Tear Glucose Levels Kyoung Ha Cha, [a] Yu Qin, [a] and Mark E. Meyerhoff* [a] 1 Introduction The World Health Organization reports that 347 million people worldwide have diabetes [1] and projects that dia- betes will be the 7 th leading cause of death in 2030 [2], de- spite the advancing modern medical science and technol- ogy [3, 4]. Tight glycemic control is essential to prevent or reduce life-threatening hyper- and hypoglycemic crises causing serious long-term complications [5]. Using a per- sonal blood glucometer with an enzymatically-active dis- posable test strip, enables diabetic patients to monitor their glucose levels by obtaining a small drop of capillary blood from their fingertips or forearms with a convention- al lancet. While minimum of four measurements of glu- cose per day is recommended to maintain normal levels of glucose in blood [6], up to eight checks per day are recommended for children and adolescents with Type 1 diabetes on insulin treatment. 7 Pricking the finger tip for many times a day can limit patient compliance and develop massive scarring/callous formation and loss of sensibility/perception hindrance. Consequently, it may lead to suboptimal blood glucose control and induce hy- poglycemia. Therefore, the development and availability of a pain-free glucose measuring device could greatly in- crease patient compliance and maintain optimal glucose control. Tear glucose measurements have been suggested as an alternative method to monitor glucose level. Tear glucose measurement techniques mandate a low micromolar LOQ, high selectivity over potential interferences such as ascorbic acid, uric acid and acetaminophen, and measure- ment within microliter or sub-microliter sample volume. Since several studies have shown that there may be a clini- cally useful correlation between blood and tear glucose levels [7–9], more detailed studies are necessary to con- firm the potential utility of tear glucose measurements to help maintain optimal glucose control. We recently re- ported [10] that Roches Accu-Chek blood glucose test strips are able to measure glucose levels in tear samples with adequate sensitivity (0.127 nA/mM) and selectivity with  13 % error (n = 3) for 25, 50 and 75 mM glucose in the presence of 10 mM acetaminophen, 100 mM ascorbic acid, and 100 mM uric acid. In this earlier work, the Roche test strips were used for measurement of glucose concentration in tears from nine normal (non-diabetic) fasting human subjects and reported glucose values were within the range of 5–148 mM (mean = 47 mM, median = 43 mM), a similar range to that reported by Asher and co- workers using an LC-MS technique. 8 Herein, we utilize bulk phase solution experiments with different enzymes, strip-based screen printed electrode materials and media- tors to explain why the Roche test strips exhibit such ex- cellent detection limits and selectivity compared to all other strips examined in our earlier studies [10]. Results indicate that the unique combination of pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ-GDH) as the active enzyme and a nitrosoaniline derivative as the electron transfer mediator are the key components of this test strip that yield the required sensitivity and selec- tivity to accurately measure low glucose levels in tear fluid. [a] K. H. Cha, Y. Qin, M. E. Meyerhoff Department of Chemistry, University of Michigan Ann Arbor, MI, 48109-1055, USA *e-mail: mmeyerho@umich.edu Abstract : Tear glucose measurements have been suggest- ed as a potential alternative to blood glucose monitoring for diabetic patients. While previous work has reported a correlation between blood and tear glucose levels in humans, this link has not been thoroughly established and additional clinical studies are needed. We recently report- ed that Roches electrochemical Accu-Chek blood glu- cose test strips exhibit far superior analytical performance over other commercial brands, with the low detection limit and high selectivity required for quantitating tear glucose levels. Herein, we evaluate the origin of the high sensitivity and selectivity of the Roche test strips and show that the use of pyrroloquinoline quinone (PQQ)-de- pendent glucose dehydrogenase (GDH) as an active enzyme reagent in combination with a nitrosoaniline de- rivative as an electron transfer mediator are primarily re- sponsible for the low limit of quantification (LOQ) (ca. 9 mM) and enhanced selectivity achieved with these strips. Keywords: Tear glucose · Roche Accu-Chek glucometer strips · Biamperometry · PQQ-dependent glucose dehydrogenase · Nitrosoaniline derivative Special Issue MATRAFÜRED www.electroanalysis.wiley-vch.de  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2015, 27, 670 – 676 670 Full Paper