A paper-based electrochemical system has been designed for flow-injection analysis of the concentration of glucose in urine samples.

Capillary wicking facilitates a gravity-driven flow of buffer solution continuously through paper and nitrocellulose, from a buffer reservoir at one end of the device to a sink at the other.

Scientists at the Vrije Universiteit (VU University; Amsterdam, The Netherlands) devised the instrument whereby difference in height between the reservoir and the sink leads to a continuous and constant flow. The nitrocellulose, on which glucose oxidase is immobilized, lies horizontally on a working electrode, which consists of a thin platinum layer deposited on a solid support. The counter and reference electrodes are strategically positioned upstream in the buffer reservoir.

A simple pipetting device was developed for reliable application of sub-microliter volumes of sample without the need of commercial micropipettes, which damage the nitrocellulose membrane. The system is based on amperometry, and the measured current is proportional to the glucose concentration. The system was tested for the determination of the concentration of glucose in 15 urine samples that had tested positive for glucose during routine analysis in the clinical laboratory. The concentration measured by the devise method resulted in a noninvasive, quantitative assay that could be used for diagnosis and monitoring of diabetes.

The system can also be used to measure glucose in other fluids, such as cell culture medium. Use of enzymes other than glucose oxidase, e.g., cholesterol oxidase, lactate oxidase, or d-3-hydroxybutyrate dehydrogenase, will enable the measurement of other metabolites, such as cholesterol, lactate, or d-3-hydroxybutyrate, respectively, making this system versatile for general clinical applications.

The authors concluded that this method does not require disposable test strips, with enzyme and electrodes that are thrown away after each measurement. Due to its low cost, this system could be used in medical environments that are resource-limited. The study was published on April 5, 2012, in the journal Analytical Chemistry.

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