Coulometry vs. Amperometry in Biosensors

The two dominant electrochemical detection methods in diabetic test strips are Amperometry and Coulometry.

Amperometry, the industry standard (used by LifeScan, Roche), measures the current generated by glucose oxidation at a specific time point. It is fast but relies on the Cottrell equation, making it sensitive to diffusion rates, which are affected by temperature, blood viscosity (hematocrit), and electrode surface area variations.

Coulometry, pioneered by TheraSense (Abbott FreeStyle), measures the total charge accumulated over time (integral of current). Based on Faraday’s Law, it quantifies the absolute mass of glucose. This method allows for extremely small sample volumes (0.3 $\mu L$) and is inherently less sensitive to hematocrit and temperature variances. While Amperometry dominates due to manufacturing speed, Coulometry drove the industry shift toward sub-microliter, painless testing.