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The prevalence of diabetes has increased from 1.4 million to 2.9 million since 1996, a statistic that is estimated to rise to 4 million by the year 2025. To combat this and explore better treatment and management options, patients undergo standard blood glucose tests.
A urine test for the diagnosis of diabetes involves submerging a test strip under a stream of urine for a period of 2–3 seconds and checking for a color change in the strip. The change in color on the sensitive test strip will indicate the percentage of glucose in the urine (a value of 0% change in color is the ideal result required for a definite diagnosis).
Blood samples are also always required to confirm a diagnosis of diabetes – a method that can be uncomfortable for patients. With the application of a non-invasive biosensor, an accurate estimation of glucose content in the body may now be possible and eliminate the use of a pinprick test.
Solution – Graphene-Based Biosensor
Researchers have developed a novel biosensor that is capable of detecting extremely small traces of glucose in human fluid, including saliva, tears, and urine. This biosensor could be plausible as production costs will not be as high due to a limited number of processing stages to make this biosensor.
This new research was led by Professor Timothy Fisher and Professor D. Marshall Porterfield, and their team at Purdue University’s Birck Nanotechnology Center. The study used a multilayered graphene petal nanosheets in an electrochemical biosensing application.
A biosensor is made up of three sections:
- Layers of nanosheets made of graphene
- A second layer made of zero-dimensional nanoparticles
- A biorecognition element - the enzyme glucose oxidase, which catalyzes the oxidation of glucose to hydrogen peroxide and D-glucono-o-lactone
The aim of this research was to develop a sensor with a broad sensing range by creating a layer of nanoparticles with topological space on a two-dimensional layer arrayed to create a 3-dimensional structure, which delivers a high level of versatility to detect glucose at concentrations as low as 0.3 microM and at a sensing range of between 0.01–50 mM.
The graphene-based biosensor generally has a shelf-life of >1 month. Interfering electroactive molecules such as uric acid, acetaminophen, and ascorbic acid (all commonly found in human samples), do not affect glucose-sensing as the biosensor has high selectivity. This makes the device particularly attractive for its application by practitioners. Thus this graphene-based biosensor could be an essential device for testing minute concentrations of glucose in blood, saliva, tears, and urine.
Figure 1. Image from a microscope showing the nanosheet layer to the new multilayer biosensor. Image Credits: Purdue University photo by Jeff Goecker. Published in an article titled: ‘Sensor detects glucose in saliva and tears for diabetes testing’.
Graphene-Based Biosensors – Functional Principle
Graphene is a sensitive nanostructure making this material robust and easy to work with. Graphene is particularly important as it has a wide electrochemical potential at 2.5 volts in 0.1 M PBS and a low charge transfer resistance that is lower than graphite. Based on its electron-transport property and high specific surface area, graphene is expected to deliver the transfer of electrons between the electrode substrates and enzymes.
The ketonic, quinonic and carboxylic functional groups on the edge plane of the graphene form covalent bonds with the free amide terminals of the glucose oxidase. This creates an anodic oxidation current of the enzymatic product H2O2, which affects the electronic structure of the graphene layer and thus provides an amperometric concentration of glucose molecules in a human sample of blood, saliva, urine, and tears.
This biosensor could mean a more efficient blood glucose testing method not only for practitioners but for diabetes patients. People living with Type II diabetes have to monitor their blood glucose regularly and often need to modify their diet and medication to prevent hyperglycemia or hypoglycemia from occurring. The problem arises when people with diabetes have to administer insulin injections and check their blood glucose several times a day to allow for better control of blood glucose. For the patients, this means a straight-forward test that isn’t invasive and time-consuming.
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