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Fluorescent glucose biosensors

Fluorescent glucose biosensors are devices that measure the concentration of glucose

in diabetic patients by means of sensitive protein that relays the concentration by means of

fluorescence, an alternative to amperometric sension of glucose. No device has yet entered the

medical market, but, due to the prevalence of diabetes, it is the prime drive in the construction

of fluorescent biosensors.

Fluorescence is a property present in certain molecules, called fluorophores, in which

they emit a photon shortly after absorbing one with a higher energy wavelength

Blood glucose monitoring is a way of testing the concentration of glucose in the blood

(glycemia). Particularly important in the care of diabetes mellitus, a blood glucose test is

performed by piercing the skin (typically, on the finger) to draw blood, then applying the

blood to a chemically active disposable 'test-strip'. Different manufacturers use different

technology, but most systems measure an electrical characteristic, and use this to determine

the glucose level in the blood. The test is usually referred to as capillary blood glucose and

sometimes incorrectly called BM Stix (after one of the companies that makes the test kit).

Healthcare professionals advise patients with diabetes on the appropriate monitoring

regime for their condition. Most people with Type 2 diabetes test at least once per day.

Diabetics who use insulin (all Type 1 diabetes and many Type 2s) usually test their blood

sugar more often (3 to 10 times per day), both to assess the effectiveness of their prior insulin

dose and to help determine their next insulin dose.

The monitoring systems currently in general use have the drawback of below optimal

number of readings, due to their reliance on a drop of fresh blood. Some continuous glucose

monitors are commercially available, but suffer from the severe drawback of a short working

life of the probe. The majority of these work amperometrically. As a result, there is an effort

to create a sensor that relies on a different mechanism, such as via external infrared

spectroscopy or via fluorescent biosensors . Various strategies exist to detect glucose levels

using fluorescence, the first and most common being a Fret competition assay between

glucose and a labelled glucose polymer for the binding site of Concanavalin A. Over the

years, using a combination of rational design and screening approaches, many possible

combinations of fluorescent sensor for glucose have been studied with varying degrees ofsuccess: In most approaches, the glucose concentration is translated into a change in

fluorescence either by using a Fret pair or by using environment sensitive (solvatochromic)

dyes.

Another pair of papers suggest that the natural fluorescence (autofluorescence) of

tissues may be harnessed to track glucose concentrations. These studies took advantage of the

fact that NAD(P)H, in its reduced form, is autofluorescent, and that metabolites such as

glucose cause a predictable increase in NAD(P)H reduction

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Ultrasound can also measure levels of glucose because sound waves are transmitted

through the tissue in the earlobe at different rates, according to how much glucose is present.

Heat also travels at a different rate through tissue when blood glucose levels are high

or low.

The ear clip device also fires low-level electromagnetic waves into the tissue - these

are transmitted differently depending on blood sugar.

Though none of these three methods is accurate enough on its own to replace blood

tests, by averaging out scores GlucoTrack can come up with a valid reading.