Wired Enzyme Technology

Wired Enzyme Technology

Wired enzyme technology connects a glucose enzyme to its electrode through an osmium-containing polymer, so the electrons that glucose gives up travel through a fixed network instead of riding on a molecule that drifts through the sample. It started in academic work at the University of Texas at Austin [1]. TheraSense, now a major part of Abbott Diabetes Care, turned it into the sensor of the FreeStyle Navigator continuous glucose monitor (CGM) [2], and Abbott researchers say the first FreeStyle Libre sensor was built on the same chemistry [3]. If you test with a meter, here is the short version: we found no FDA record or Abbott account that describes a wired enzyme test strip.

What "wiring" an enzyme means

An enzyme pulls electrons off glucose, and something has to carry them to an electrode, where the device counts them as current. That carrier is called a mediator. In Abbott's FreeStyle strips, an osmium mediator picks up electrons from the enzyme and hands them to a carbon electrode. Because it can move, the designers had to keep it from shuttling electrons between two facing electrodes only 50 micrometers apart [2].

Wiring takes the moving part out. In 1990, Brian Gregg and Adam Heller described glucose oxidase "wired" to an electrode by a redox polymer (a polymer chain studded with groups that can each accept and give up an electron), so electrons flow from the enzyme, through the polymer, to the electrode [1]. Crosslinking their osmium polymer with the enzyme formed a tough film on the electrode, so no membrane was needed to hold the two in place [1]. Abbott's 2017 description of the FreeStyle Libre sensor uses the same picture: neighboring osmium mediator molecules, crosslinked with the enzyme, relay electrons to the working electrode [3].

Here's what surprised us: the first wired electrodes lost a good share of their signal to oxygen. Currents fell by 30 to 50 percent in air, because oxygen competed with the osmium for the enzyme's electrons [1]. By 1994, Heller's group was using an osmium hydrogel, a water-swollen polymer network, and reported that with the electrode held at 200 mV, currents from ascorbate (vitamin C), urate, acetaminophen and L-cysteine were negligible [4].

From a university lab to TheraSense and Abbott

A 1995 paper from the Texas group described a flexible wire electrode 0.29 mm across, built for implanting under the skin. None of its layers contained leachable components, and its sensitivity dropped less than 4 percent over a week of continuous operation at body temperature [5]. In a 2003 TheraSense study, 48 Wired Enzyme sensors were worn for 3 days by people with type 1 diabetes, and 98 percent of readings fell in the clinically accurate or acceptable zones (A and B) of the Clarke error grid [6].

FDA approved Abbott Diabetes Care's FreeStyle Navigator on March 12, 2008. Its sensor was designed for up to five days of wear, and the receiver had a FreeStyle blood glucose meter built in for calibration [7]. FDA's summary doesn't name the chemistry [7]. Heller and Feldman do: the Navigator's catalyst was glucose oxidase crosslinked with a wiring redox hydrogel holding a polymer-bound osmium complex. Very little current flowed when no glucose was present, which helped the system work with one-point calibration [2].

FDA approved the original 10-day FreeStyle Libre on September 27, 2017, as a system calibrated at the factory that neither required nor accepted fingerstick calibration [8]. That year, Abbott researchers wrote that the Libre chemistry is based on the Wired Enzyme technology used in the Navigator, with a working electrode that needs only 40 mV against a silver/silver chloride reference, which minimizes oxidation of interfering substances [3]. They list sensor stability and a robust manufacturing process as the requirements for factory calibration [3].

That 10-day sensor has been replaced: as of October 2026, Abbott's current US sensors are the FreeStyle Libre 2 Plus and Libre 3 Plus, cleared together in April 2024. FDA's review says they use glucose oxidase to oxidize glucose and transfer electrons to an electrode, without saying whether a wired osmium polymer carries them [9].

Where [test strips](/sell-diabetic-supplies/) fit

FreeStyle strips share the brand and the TheraSense history, but the records describe a different setup. The first FreeStyle strip became available in 2000 and measured glucose in 300 nL of blood. Heller and Feldman describe its chemistry as glucose dehydrogenase (GDH) plus an osmium mediator that takes electrons from the enzyme and gives them up at the carbon electrode. In the same account they call the Navigator "enzyme-wiring based" and don't use that label for the strip [2].

FDA's decision summary for FreeStyle Lite strips (510(k) K092602) describes a coulometric test, one that counts the total charge over the reaction time, using FAD-dependent GDH. The electrons are "transferred via a co-factor and mediator" to the meter, and the summary doesn't mention wiring [10]. Our article on coulometry vs. amperometry explains that difference.

Neither record describes a wired strip, though neither says outright that the strip isn't wired. Our article on mediator chemistries compares osmium with other brands' mediators.

What the patents claim

A patent shows what inventors claimed, not what any product contains.

US Patent 5,262,035, "Enzyme electrodes," was filed by Brian Gregg and Adam Heller in August 1989 and granted in November 1993, with Heller E and Co as the original assignee. Claim 1 is the wiring idea in one sentence: an electrode coated with a crosslinked polymer that has multiple redox centers, with a redox enzyme bound inside and the polymer connecting the two electrically. Google Patents lists Abbott Diabetes Care and the University of Texas System as current assignees and shows the patent as expired [11].

US Patent 6,299,757, "Small volume in vitro analyte sensor with diffusible or non-leachable redox mediator," was granted to TheraSense in October 2001. Its abstract covers either kind of mediator, and its background warns that a diffusible mediator can shuttle between closely spaced electrodes and add to the signal. Claim 1, though, is about strip layout, including indicator electrodes that show when the sample chamber is full [12].

US Patent 8,636,884, "Cationic polymer based wired enzyme formulations for use in analyte sensors," was filed by Abbott Diabetes Care in September 2008 and granted in January 2014. Claim 1 covers an implantable electrode in which a glucose enzyme hands electrons to a positively charged redox mediator held in a cationic polymer [13]. The record doesn't tie it to a product.

What we still don't know

We didn't find a head-to-head study comparing the accuracy or speed of wired enzyme sensors with other CGM chemistries, and the trial and design papers we relied on come from TheraSense and Abbott authors [6] [3]. The biggest open question is whether the Libre 2 Plus and Libre 3 Plus sensors sold as of October 2026 still use the osmium polymer. FDA's public summary doesn't answer it [9].