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Inexpensive Built-In Timer Improves Accuracy of Paper-Based IVD Devices

November 3, 2010 – 9:14 am

Time's up! A colour change on the diagnostic device indicates when the test result is ready. Image courtesy Scott T. Phillips.

Here’s a classic example of someone building the proverbial better mousetrap: A simple timer built into diagnostic devices improves the accuracy of paper-based IVD products. Many types of tests that could be used on paper require the use of a stopwatch to precisely time the process and provide accurate results. Diagnostic products with a built-in timer would be especially beneficial for patients in the developing world who may not have access to those devices or who may use external timers that are not accurate enough to obtain meaningful results. Scientists Scott Phillips and Hyeran Noh have published their study in the semi-monthly journal Analytical Chemistry.

Point-of-care tests show special promise for improving medical care in developing countries and reducing healthcare costs elsewhere. Moreover, low-cost paper tests, when fully developed, may replace more expensive traditional tests for detecting biomarkers in urine, blood and other body fluids. As one example, Phillips and Noh cite the CHEMCARD diagnostic test for measuring blood sugar or cholesterol in a drop of blood. It is almost 100% accurate when users view test results exactly three minutes after placing the drop of blood on the paper. Incorrect timing, however, cuts accuracy nearly in half.

In the article, the scientists describe the development of a built-in timer for paper-based diagnostic tests that eliminates the need for a stopwatch. The timer is made from a dye and the paraffin wax used in some candles. Addition of water, blood, urine or other body fluids starts the timer, and a colour change signals when the time is up. The device has been modified to emit a buzz or other sound, or even to glow, when the test results are ready, the scientists note. When used with a test similar to the CHEMCARD glucose test, the timer was 97% accurate, slightly better than when a stopwatch was used.