Continuous Glucose Monitor (CGM) Sensor Fabrication

Introduction to CGM Sensor Fabrication

A test strip works once, for a few seconds, on a drop of blood. A CGM sensor has to keep working for days to weeks in the fluid under the skin, while the body treats it as a foreign object [1].

That is why fabrication carries so much weight. Abbott's sensor engineers write that the sensing area is smaller than 1 mm² and the glucose-limiting membrane is typically thinner than 100 µm, so small differences between sensors show up as differences in the reading [1].

Key Fabrication Pillars

We grouped what we read into four pillars. The second one, chemistry, is where manufacturers differ most:

• Geometry: Abbott and Dexcom build their sensors in different shapes, planar and wire-based.

Abbott uses screen-printed planar sensors on flexible polymers, while Dexcom uses Pt-Ir wire with dip-coatings. FDA records confirm the wire: the FDA's decision summary for the Dexcom G6 warns that a broken sensor wire could stay under the skin [4]. Dexcom stopped manufacturing the G6 after July 1, 2026, and is moving users to its G7 sensors [5].

• Chemistry: There is no single CGM industry chemistry. As of October 2026, the sensors we looked at use one of three designs.
• Dexcom: the enzyme glucose oxidase reacts with glucose and produces hydrogen peroxide, and the electrode turns that peroxide into a current proportional to glucose. The FDA describes the Dexcom G7 this way [3].
• MiniMed: the sensors Medtronic developed, such as the earlier Enlite sensor, are also glucose oxidase sensors [6], and the classic form of that design measures hydrogen peroxide at a platinum electrode [7]. MiniMed's 780G system now also works with the Instinct sensor, which Abbott makes [10].
• Abbott: "Wired Enzyme" technology. Glucose oxidase still does the first step, but an osmium complex carries electrons from the enzyme to the electrode [1]. Here's what surprised us: the chemistry doesn't remove oxygen effects entirely. Its developers described "reduced susceptibility" to changing oxygen levels in the body, plus a smaller response to common interfering substances [2], which Abbott credits to running the electrode at a low electrical potential [1]. The FDA's summary for the FreeStyle Libre 2 and 3 systems also describes the enzyme handing electrons to an electrode [8].
• Eversense: no enzyme at all. The Eversense 365 implant measures glucose optically. Glucose binds reversibly to a fluorescent indicator on the sensor, and the sensor reads the change in light [9].
• Membrane Engineering: Multi-layer membranes limit how fast glucose reaches the enzyme. Abbott's engineers rank that flux-limiting membrane, along with the enzyme layer, as the most critical part of the sensor [1]. The layers also help block electrochemical interferents; Dexcom, for example, designed the G6 sensor to reduce the acetaminophen interference seen in earlier Dexcom systems [4]. Finally, the design has to minimize the Foreign Body Response, or keep it from disturbing the signal, so sensitivity stays stable through the wear period [1].
• Factory Calibration: In factory calibration, the calibration step happens during manufacturing under laboratory conditions, and each sensor lot gets a code that converts the sensor's current into a glucose value [1]. That only works if every sensor in a lot behaves alike, which depends on precise control of electrode area and membrane thickness [1]. Abbott's FreeStyle Libre sensors were the first commercially available CGM sensors calibrated this way [1]. The Dexcom G7 is factory calibrated, with manual calibration optional [3]. Not every CGM skips fingersticks, though. The Eversense 365 needs four fingerstick calibrations after its 24-hour warm-up, then one a day through day 13, then one a week [9].

Conclusion

These choices explain why CGMs that all report a glucose number can behave differently in the body. A Dexcom, an Abbott and an Eversense sensor rely on peroxide detection, an osmium mediator and fluorescence respectively [3] [1] [9]. One thing we could not pin down in FDA summaries or the papers we read: the exact electrode materials and coating steps each company uses.