A novel pain-free device is under development that could detect tear-glucose levels, rather than having to go through the cumbersome and sometimes painful routine of drawing blood

At the University of Michigan (Ann Arbor, MI, USA), scientists have developed an amperometric needle-type electrochemical glucose sensor intended for tear glucose measurements. It is used in conjunction with a capillary tube to collect microliter volumes of tear fluid. The glucose sensor was employed to measure tear-glucose levels in anesthetized rabbits over an eight-hour period while also measuring the blood glucose values.

The sensor was calibrated in capillary tubes with 100-µM glucose in the middle of the 8-hour experiment. Every 30 minutes, 0.6 mL of blood was drawn and the blood glucose level was measured using a Radiometer ABL 725 blood analyzer (Radiometer America Inc., Westlake, OH, USA) that employs a macro-electrochemical enzyme electrode to quantitate blood glucose. At the same time, 5 µL of rabbit tear fluid was collected in the capillary and the current from the glucose in the tear fluid was recorded using the tear glucose sensor.

The sensor was extremely sensitive and can achieve extremely low detection limits of 1.5 ± 0.4 µM of glucose. This is enough to measure tear-fluid glucose levels, with a glucose sensitivity of 0.032 ± 0.02 nA/µM. The sensor's capillary tube only requires 4-5 µL of tear fluid when the needle sensor is inserted into the capillary. A strong correlation between tear and blood glucose levels was found, suggesting that measurement of tear glucose is a potential noninvasive substitute for blood glucose measurements, and the new sensor configuration could aid in conducting further investigations in this direction.

Patients with diabetes may have to draw blood from about two to ten times daily to test their blood glucose levels. A considerable number of diabetics do not draw blood as often as they should, because of the discomfort and pain it causes. This may lead to poor glycemic control. Long-term poor glycemic control increases several risks and complications linked to the condition, especially microvascular complications which can lead to neuropathy and the development of foot ulcers, retinopathy and other diseases and conditions. The study was published on September 30, 2011, in the journal Analytical Chemistry.

Related Links:
University of Michigan
Radiometer America Inc.