Paper-Based Diagnostic Test Developed For Diabetes

A device has been developed that measures glucose in urine samples and is made from inexpensive materials.

The device consists of three electrodes, a buffer solution, a piece of paper (or nitrocellulose) and a plastic dish. The sample is injected onto the paper with a slightly modified medical syringe, and the solution moves along the paper by gravity and capillary action.

Scientists at the University of Maryland (Baltimore, MD, USA) developed the system to replace current handheld diabetes monitoring devices, which measure glucose levels in blood, which requires a pinprick to a finger, something that could deter patients from taking the measurements. An enzyme called glucose oxidase is already on the paper, and it reacts with glucose in the sample to produce hydrogen peroxide, which is detected by the electrodes. The system can be built quickly, is inexpensive, and it produces results similar to those from a more expensive, commercially available clinical instrument.

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. A difference in height between the reservoir and the sink leads to a continuous and constant flow. The nitrocellulose 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; this device did not damage the nitrocellulose membrane.

The system is based on amperometry, and the measured current is proportional to the glucose concentration. The maximum height of the signal can be directly related to that of a glucose standard. This system can be constructed rapidly, and it is inexpensive. The amplifier that reads out the current from the working electrode costs less than USD 30 for off-the-shelf components. With epidemics of Type 2 diabetes looming in rural India, China and other areas of the world where poverty limits the availability of health care, the development of an inexpensive and easy-to-use urine test is ideally suited for such areas.

The authors concluded that other applications of this methodology could be used such as measuring urinary creatinine or lactate concentrations with appropriate enzymes. The system also has the potential for multiplexing, measuring metabolites in series when the sample passes locations where different enzymes have been spotted on the nitrocellulose. It can also be used as a low-cost detector for micro high-performance liquid chromatography for urine, food, or environmental analysis. The study was published on April 5, 2012, in the journal Analytical Chemistry.

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