Electrode Material Composition (Carbon vs. Gold/Palladium)

Electrode Material Composition

The working electrode is the conductive surface on a test strip where the glucose signal is measured. Strips build it in one of two main ways: carbon ink printed as a relatively thick layer (thick film), or a metal such as gold or palladium laid down as a very thin layer (thin film). We expected that split to track price, with metal in brand-name strips and carbon in budget ones. The sources we read don't support that. Abbott's FreeStyle strips were built on a printed carbon electrode [2], while LifeScan's OneTouch Verio strips use thin-film gold and palladium [1].

Screen-Printed Carbon (Thick Film)

Most disposable point-of-care glucose strips rely on screen-printed electrodes, according to a 2010 clinical review [3]. Printed carbon is usually described as the lower-cost option, with higher electrical resistance and a rougher surface than a metal film.

Carbon isn't limited to store brands. Here's what surprised us: the FreeStyle system, developed by TheraSense (now part of Abbott Diabetes Care) and on the market since 2000, was described by its developers in 2010 as a printed carbon electrode facing a printed silver/silver chloride electrode across a gap of 50 micrometers [2].

To understand the voltage question, it helps to know what a mediator is. It's a chemical that carries electrons from the strip's enzyme to the electrode, where the meter reoxidizes it and reads the resulting current [3]. The FreeStyle team picked an osmium-based mediator with a formal potential between 0.0 and −0.2 V relative to the facing silver/silver chloride electrode [2]. That is a carbon strip running at a low potential, so carbon by itself doesn't force a high operating voltage.

Noble Metals - Gold/Palladium (Thin Film)

LifeScan's researchers described the OneTouch Verio strip in 2012 as a palladium electrode and a gold electrode facing each other, separated by a thin spacer [1]. The two metals do different jobs. Glucose-sensing reagents sit on the palladium electrode, where a ferrocyanide mediator carries the glucose signal; the meter measures mediator reaching the upper gold electrode early in the test to estimate hematocrit, the share of the blood made up of red cells [1]. In LifeScan's own testing, all 2,700 results across hematocrit levels of 19% to 61% met the ISO accuracy criteria in force at the time [1].

Metal electrodes are credited with more precise surface areas and faster electron transfer than printed carbon. They're also often credited with lower operating voltages, but that part belongs mostly to the mediator. The meter has to apply enough potential to reoxidize whatever mediator the strip uses [3], which is how Abbott ran a carbon strip at a low potential [2]. A lower potential does help accuracy: an interfering substance is any molecule in the blood that reacts at the sensor's operating potential, such as acetaminophen or ascorbic acid [3].

Gold also doesn't have to come as a vapor-deposited film. Bionime, a strip maker, built strips from two barrel-plated gold electrodes inserted into a molded plastic base. In heat-aging tests it reported in 2009, they held up better than vapor-deposited palladium and screen-printed carbon platforms [4]. That is a manufacturer's study of its own design, so we read it as one data point.

We didn't find evidence of an industry-wide move from carbon to metal, since two major brands sit on opposite sides. Every design does face the same accuracy bar. Under ISO 15197:2013, at least 95% of a system's results must fall within ±15 mg/dL of the comparison method below 100 mg/dL, and within ±15% at or above 100 mg/dL [5]. Those criteria are written in terms of measurement results, so the electrode material is the manufacturer's choice.