Microfluidic Paper-based Analytical Devices (μPADs): Miniaturization and Enzyme Storage Studies

This paper describes the design and development of miniaturized microfluidic paper-based analytical devices ( PADs) for biological assays and enzyme storage instruments. Here, a glucose assay utilizing glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (ICI) is used as the model system. The efficacy of the miniaturized devices is further examined by assessing the activity of acetylcholinesterase (AChE). Two types of mu tPADs were developed: one, "strip" chips of detection zones of area 0.5, 0.1 cm(2) and, two, "grid" chips of detection zone 0.05 cm(2). The devices are easily fabricated via a wax printing process whereby lines of wax are deposited onto chromatographic paper and heated to create rows of hydrophobic barriers. The "strip" chips were subjected to three different temperature environments (-20, 0, and 20 degrees C) over 30 days and glucose assays conducted at intermittent times yielding a correlation between corrected average inverse yellow intensity, days, and glucose concentration. Calculated and experimentally derived color intensity values for 1, 4, and 9 mM glucose concentrations after a 7-day storage study showed a good correlation (0.89 - 15.76% error). Both types of PADs are effective platforms as potential point-of-care (POC) diagnostic devices and display minimal enzyme denaturation. mu PADs of this size show promise as alternative devices for resource-limited regions and especially those areas where materials and instrumentation are not always available.