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FROM CHEMISTRY TO PRODUCT

Three big jobs

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Make the electrode

Form thin metal or carbon electrodes on a wire or film

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Add the layers

Apply the enzyme and each membrane in a controlled thickness

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Package it

Cure, sterilize, and assemble it into an applicator

The chemistry from earlier units has to be repeated millions of times, identically.

MATERIALS

What the electrodes are made of

Platinum A very effective, stable catalyst for oxidizing hydrogen peroxide, but expensive
Gold Inert and easy to deposit as a thin film
Carbon Inexpensive, and can be printed from inks
Silver/silver chloride The standard reference electrode material
Material choice trades cost, catalytic activity, and stability.

BUILDING LAYERS

Ways to put them down

Dip coating A wire is dipped repeatedly to build up thin layers
Screen printing Inks printed through a mesh to form electrodes and layers on flat strips
Thin-film deposition Metals sputtered and patterned with photolithography, as in the MEMS course
Inkjet spotting Tiny droplets place precise amounts of enzyme
Layer thickness sets sensitivity, so it must be controlled very tightly.

SURVIVING THE FACTORY

The enzyme has to make it to your arm

Sterilization Sensors must be sterilized, and the process must not destroy the enzyme
Storage Heat and humidity can degrade enzyme layers, so shelf life is limited
Uniformity Factory calibration only works if every sensor in a batch behaves alike
A very reproducible process is what makes calibration-free sensing possible.

THE PROCESS

Five steps to a sensor

Making a sensor 1electrode2layers3cure4sterilize5calibrate Factory calibration only works if every sensor in a batch behaves alike
These are the same thin-film and coating tools you met in the microfabrication courses.

UNIT 15 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered the materials, methods, and manufacturing limits behind a CGM sensor.