FROM MOLECULE TO CURRENT

Counting electrons

Each hydrogen peroxide molecule that reacts at the electrode releases a fixed number of electrons. A flow of electrons is a current. Measuring that current, which is called amperometry, measures how fast glucose is being converted.

More glucose means more electrons per second, and a bigger current.

THE CELL

Three electrodes, one fluid

The working electrode is where the reaction happens and the current is read. The reference electrode, often silver and silver chloride, provides a stable voltage standard. The counter electrode completes the circuit.

A small circuit called a potentiostat controls all three.

HOLD THE VOLTAGE

A fixed push on the electrons

The job A potentiostat holds the working electrode at a fixed voltage relative to the reference

The voltage Oxidizing hydrogen peroxide at platinum takes about +0.6 V

The reaction H₂O₂ → O₂ + 2H⁺ + 2e⁻, so each molecule gives two electrons

Hold the voltage steady, and the current becomes the glucose signal.

THE EQUATION

Current tracks flux

i = n · F · A · J

n Electrons released per molecule, which is 2 for hydrogen peroxide

F The Faraday constant, about 96,485 coulombs per mole of electrons

A Electrode area

J How many molecules react per second per unit area (the flux)

Current is proportional to the flux of reacting molecules.

CALIBRATION CURVE

From nanoamps to mg/dL

Sensor currents are tiny, usually nanoamps. Over a useful range the current rises in a straight line with glucose. At very high glucose the enzyme or oxygen is used up, and the line flattens.

A calibration curve is the recipe for converting current into a glucose reading.

UNIT 6 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered how reaction products become a current, and how that current is calibrated.