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Carbon Nanotube Sensor Detects Glucose in Saliva

Painful finger-prick blood tests for diabetics could become a thing of the past, say physicists who have built a sensor that measures glucose in saliva

Diabetes affects some 300 million people worldwide and the numbers keep on increasing. Many of these people undergo a daily regimen of tests that measure the amount of glucose in the blood stream, usually taken from finger prick samples.

Needless to say, this is a time-consuming, expensive and painful process. So a cheap way of measuring blood glucose that does not require finger pricking would clearly be advantageous.

Today, Mitchell Lerner at the University of Pennsylvania in Philadelphia, and a few pals, say they have developed just such a device. Their glucose sensor is essentially a carbon nanotube-based transistor in which the never tubes are coated with pyrene-1-boronic acid molecules that bind to glucose.

The device is relatively simple. It’s straightforward to measure the switching characteristics– the current-voltage curve– of a transistor. When glucose binds to the functionalised nanotubes, it simply changes this curve in a measurable way producing a straightforward way to measure glucose concentration.

Much of this technology has already been demonstrated in the lab. The trick that Lerner and co have perfected is to combine it in an easy-to-make system that is potentially cheap to manufacture en masse.

 Lerner and co have tested their new device in a clinically-relevant range of glucose concentrations and say it is sensitive enough to detect glucose changes, not only in blood, but in other body fluids such as saliva. “Such devices would potentially eliminate the need for frequent, uncomfortable finger pricking for blood glucose measurements and would greatly improve diabetic peoples’ quality of life while still maintaining a high level of diagnostic accuracy,” they say.

That certainly looks an important breakthrough, particularly for people with Type II diabetes who do not need insulin injections and who make up the vast majority of sufferers. The prospect of saliva-based tests for them will make life significantly easier.

For Type I patients, who must inject insulin several times a day, the new system will be less useful. The problem is that it takes time for changes in the blood sugar levels to be reflected in the saliva. And that means the concentration of glucose in the saliva always lags that in the blood by around 30 minutes or so. That’s long enough to cause serious problems if, for example, sugar levels in the blood are dropping precipitously.

Nevertheless, carbon nanotube-based sensors could be significantly cheaper and more robust than the enzyme-based ones that are commonly available today. And that in itself is an important factor for healthcare systems already overburdened by the high cost of treating this disease.

There is a bigger picture, however. What’s needed is a simple, cheap and reliable way of monitoring sugar levels directly in the blood and connecting this to a system that administers the correct dose of insulin in real time. There is no shortage of people working on such a system with important advances being made in areas such as stem cells and with an artificial pancreas. It is in these areas that the biggest advances for people suffering diabetes are likely to occur.

Ref: arxiv.org/abs/1304.7253: Scalable, Non-Invasive Glucose Sensor Based on Boronic Acid Functionalized Carbon Nanotube Transistors

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