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Biosensors: What are they? - Isabella R.

Going to the doctor’s might be daunting sometimes. I’m sure we’ve all at some point said to anyone listening, “I don’t want to go!” But, what if you were able to stop these monotonous visits and instead check these vitals on your phone, for example? Or simply avoid the terrifying needles and various tests altogether?

A biosensor is a typically small, highly organised device that allows for the measurement of biomarkers in the body (molecules that are analysed in order to give an idea about the health and disease of the user).

The biosensor can act directly on the body (like the glucose sensors you might often see being used by patients who have diabetes), in which case the device gives continuous readings. Or, the biosensor can act outside the body, in which case one needs to add direct samples of biomarkers from the body (ie blood) for them to be analysed and interpreted each time one desires a reading.

You might be wondering what the point of these seemingly unnecessary devices is. Well, one of the main advantages of a biosensor is that doctors are always able to obtain the information they need in order to improve the patient’s treatment, stop any unnecessary hospital visits (which might be time-consuming and costly), and aid the user in self-regulation of their lifestyle (since the users themselves have a direct indicator of their health). In this way not only is the treatment of the disease made more effective, but so too is the diagnosis! In other words, one can detect a disease much sooner through constantly measuring of a person’s vitals!

There are 4 main components to a biosensor:

  1. Molecular recognition process: they contain recognition molecules which bind to the biomarker. The recognition molecules themselves are biological molecules such as an aptamer, enzymes or antibodies, which are able to interact with the biomarker and bind to it.

  1. Signal generator process: when the recognition molecule binds to the biomarker, a signal is produced which can be 1) and electoral signal 2) a magnetic signal 3) an optical signal.

  1. Disposable sensor device: the previous two processes of the molecular recognition and signal generator processes occur here.

  1. Reader instrument: this device interprets and measures the signal produced in the signal generator process, and projects it as familiar and meaningful data to the user. These reader instruments can incorporate piezoelectric properties, which will be discussed now, that can ultimately produce an electrical signal which can be redirected to your phone!

The piezoelectric effect allows us to convert a mechanical change (which can be caused by a mass change, and so, inherently, by any chemical reaction also!) into an electrical signal. In order to do this, we require a piezoelectric material, which can generate voltage when external stress (a mechanical action) is applied. An example of this material is “Quartz Crystal”, a piezoelectric crystal. Quartz crystal consists of a hexagonal arrangement of Si and O bonded together. Due to the difference in electronegativity between Silicon and Oxygen (with the oxygen being more electronegative and the Silicon being less electronegative), a permanent dipole is created in their bond (with oxygen being delta negative and the silicon being delta positive). This permanent dipole acts across the hexagon, and due to its unique arrangement, the charge is all concentrated at the centre.

Yet, when a force is applied to our material, this centre of charge of negative and positive charges no longer coincides, ie: now there is a positive concentration of the charge and a negative concentration of the charge. This process creates an electric field between the positive and negative charges, an electric current. On a larger scale, numerous small potential differences across each molecule add up to a larger voltage created when more hexagons are being used. So, by applying stress to a polarised material, we are able to generate an electric current. The more hexagons (which act as cells) we have, the more voltage is created from this piezoelectric effect!

Then, this electrical signal which has been produced can be reincorporated as a vibration or a resonance frequency which is afterwards read by a reader instrument on the biosensor. To facilitate detection, the reader instrument can redirect its signal via bluetooth to an application on a phone or computer, for example.

By implementing biosensors therefore, not only will the ordeal of going to the doctors decrease, but personalised medicine and effective diagnosis and treatment will increase. What a fascinating prospect!

Isabella R

Year 12

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