MICRONEEDLES

Reach the fluid, skip the pain

A microneedle is only hundreds of microns long, just enough to reach interstitial fluid in the upper skin, while staying short of most nerves. Some designs put sensing electrodes on solid needles, and others use hollow needles to draw fluid out. Many are still in research or early development.

Microneedles use the same microfabrication tools as MEMS devices.

OTHER FLUIDS

Sweat, tears, and saliva

The appeal No needle at all, and easy access

Concentration Glucose is much more dilute than in blood, so signals are small

Variability Sweat rate, skin contamination, and temperature change the reading

Examples Skin patches, smart contact lenses, and mouthguards, mostly in research

The lag and variability are usually larger than for tissue-fluid sensors.

LIGHT THROUGH SKIN

Optical non-invasive sensing

Methods Near-infrared and mid-infrared absorption, Raman scattering, and photoacoustics

The signal Glucose's optical fingerprint is tiny compared with water, skin, and blood

The noise Temperature, motion, and skin differences swamp it

The record Decades of attempts, but no non-invasive method has matched invasive CGMs

The signal-to-noise problem is the hardest part.

A REAL WARNING

Smartwatches do not measure glucose

In 2024 the U.S. FDA issued a safety communication warning people not to use smartwatches or smart rings that claim to measure blood glucose without piercing the skin. It said no such device had been authorized, and that inaccurate readings could lead to wrong treatment decisions.

Extraordinary claims about glucose sensing need extraordinary evidence.

WHY IT IS HARD

The bar is very high

Selectivity Glucose must be separated from many look-alike signals

Accuracy Clinical use needs errors that stay small across the whole range

Lag A reading that arrives late can mislead during fast changes

Calibration The sensor must work across different people and conditions

Meeting all four at once is why the minimally invasive CGM won out.

UNIT 16 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered the less invasive routes to glucose sensing and why none have replaced CGMs yet.