Glucose Sensors: What They Are & How They Work
Glucose sensors are biosensors designed to detect glucose levels, which is vital to managing diabetes. But do you know how the technology actually works?
Whether in the form of a test strip for a blood glucose meter or a sensor for a continuous glucose monitor, the detection and measurement of glucose levels are similar processes. Read on to learn how biosensors work, including the different types of glucose sensors.
- What is a Biosensor?
- How Does a Glucose Sensor Work?
- The Different Types of Glucose Sensors
What is a Biosensor?
According to the Oxford Dictionary: “A biosensor is a device that uses a living organism or biological molecules, especially enzymes or antibodies, to detect the presence of chemicals.”
Biosensors can be part of a single-use test kit or a long-term monitoring device. Each system uses a combination of elements for the rapid detection and measurement of specific molecules.
There are a wide variety of applications for biosensors, and they are used most commonly in healthcare settings. Because of their ability to be highly selective, sensitive, and relatively easy to use, biosensors can rapidly recognize and measure key biometrics in bodily fluids to aid in health monitoring. Examples of commercially available biosensors include:
- At-home pregnancy tests
- Blood glucose meters
- Continuous glucose monitors
- Cholesterol meters
How Does a Glucose Sensor Work?
Glucose testing tools — like glucose meter test strips and wearable sensors — are glucose biosensors. These compact devices are comprised of several crucial components for the detection and measurement of glucose.
The National Center for Biotechnology Information (NCBI) features an exhaustive explanation of the parts of a biosensor.
For a glucose biosensor, the following components are used:
- Analyte: A substance with chemical constituents that are being identified and measured. In this instance, glucose is the analyte that the biosensor is designed to detect.
- Bioreceptor: This is a molecule that specifically recognizes the analyte. For the detection of glucose, specific enzymes are used, which are proteins that facilitate a chemical reaction. For example, the test strip for a blood glucose test contains the enzyme that interacts with the analyte in the drop of blood.
- Transducer: This part of the biosensor converts one form of energy into another. Specifically, it converts the recognition of the bioreceptor into a measurable signal. Most modern-day glucose meters and continuous glucose monitors measure electrical signals, although earlier generations of glucose meters used a colorimetric process (color change) that was measured optically.
- Electronics and display: These components process the transduced signal and prepare it for display. The processed signals are then quantified and shown on either the glucose meter’s display or the receiver for a continuous glucose monitor (or compatible app).
The Different Types of Glucose Sensors
Glucose sensors come in either a discrete form (blood glucose meter test strips) or wearable form (a continuous glucose monitor). Although the form factors look different to the user, both types of glucose sensors use similar detection methods. For example, a glucose oxidase biosensor could be in the form of a test strip or a wearable CGM sensor.
In order to create the chemical reaction that allows glucose to be detected in a bodily fluid, different bioreceptors can be used. The most common type of glucose sensor is enzyme-based. The enzyme coating on the glucose sensor allows it to react with the analyte and produce a secondary species that can be measured electrochemically.
Common enzymes (bioreceptors) that are used to detect glucose include:
- Glucose oxidase (GOx)
- Glucose dehydrogenase nicotinamide adenine dinucleotide (GDH-NAD)
- Glucose dehydrogenase flavin adenine dinucleotide (GDH-FAD)
- Glucose dehydrogenase pyrroloquinoline quinone (GDH-PQQ)
- Note: This enzyme has been phased out, as it reacts with other sugars like maltose, galactose, and xylose.
Once the reaction takes place, the electrical signals can be measured by either the blood glucose meter or the continuous glucose monitor to provide a glucose reading.
Blood Glucose Sensors
Blood glucose meters are one of the oldest and most common methods for testing glucose. These devices use enzyme-coated test strips that are manufactured with a precise amount of specific enzymes that can only react to one blood sample. Because of this, test strips are intended for single use and cannot be reused. When inserted into the blood glucose meter and after receiving a blood sample, the test strip communicates with the glucose meter which calculates the amount of glucose in the blood and displays the result on the meter’s screen.
The cost of blood glucose meters and test strips is typically more affordable than continuous glucose monitoring devices. Meters also provide more discrete and intermittent testing, since they don’t need to be worn on your body.
For more details on blood glucose meters, read Choosing the Best Glucose Meter for Your Needs.
Continuous Glucose Sensors
A continuous glucose monitor (CGM) uses a filament coated in glucose sensing enzymes to detect glucose in the interstitial fluid (the fluid between your cells). As a wearable sensor, a CGM automatically detects and measures glucose levels 24 hours a day.
A CGM sensor can be used continuously for several days or weeks — the exact duration will vary by manufacturer. Implantable CGM sensor options offer months-long wear, as they are embedded below the skin in a larger capsule, versus the thinner filament in other CGM sensors.
The sensor then works with a transmitter that sits above the skin to send data to a receiver or smart device. The transmitter allows you to wirelessly view your current glucose level and trends, or you can be notified when it’s time to replace the sensor.
The cost of a CGM device will vary by brand, but it is often more expensive than using a blood glucose monitor. This is because the CGM requires the ongoing replacement of more costly sensors and transmitters.
How and Where Are CGM Sensors Inserted?
With the aid of a needle, the sensor is inserted under your skin. Needle-free options — like the long-wear WaveForm CGM — are also available to reduce complications and minimize pain from insertion.
The recommended areas for insertion most commonly include the abdomen or back of the arm, but the CGM manufacturer will provide exact recommendations to where their product should be placed. To ensure that the sensor remains in place, an adhesive patch (like a BAND-AID®) holds the sensor to your skin.
Learn more about CGMs in our article, Understanding Continuous Glucose Monitoring.