THE CHALLENGE

Find one sugar in a messy fluid

A glucose sensor must pick out glucose from many other molecules, including other sugars, drugs, and vitamins. It must do it in a warm, protein-rich fluid, at low signal levels, and keep working for days or weeks.

Two properties matter most: selectivity for glucose, and stability over time.

THREE FAMILIES

Ways to turn glucose into a signal

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Electrochemical

A reaction with glucose produces electrons, which become a current

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Optical

Glucose changes how a material absorbs, scatters, or gives off light

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Other fluids

Sensing glucose in sweat, tears, saliva, or breath instead of tissue fluid

Almost every commercial CGM sold today uses the first two.

ELECTROCHEMICAL

With an enzyme, or without

Enzymatic An enzyme such as glucose oxidase reacts only with glucose, which gives excellent selectivity

Non-enzymatic A metal such as platinum, gold, or nickel oxide catalyzes glucose directly, which is simpler but less selective

Today Commercial CGMs use enzymes. Non-enzymatic designs are mostly still research

The enzyme is what lets the sensor ignore everything that is not glucose.

OPTICAL

Using light instead

Fluorescence A glucose-binding material changes how brightly it glows. Used in implantable CGMs

Infrared and Raman Light shone through skin carries a tiny glucose fingerprint buried in other signals. Mostly research

Affinity materials Gels or proteins that bind glucose and swell or change color when they do

Optical methods avoid consuming a reaction, but the glucose signal is often very weak.

WHO USES WHAT

The commercial landscape

Dexcom Enzymatic, electrochemical, worn on the skin

Abbott FreeStyle Libre Enzymatic, electrochemical, worn on the skin

Medtronic Guardian Enzymatic, electrochemical, worn on the skin

Senseonics Eversense Fluorescence-based, implanted under the skin

The next units open up how each of these works and how they differ.

UNIT 4 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered the main ways to sense glucose and which ones real CGMs use.