Mediator Chemistry and Electron Transfer

The evolution of diabetic test strips is defined by the shift from Oxygen-dependent (1st Gen) to Mediator-based (2nd & 3rd Gen) electron transfer systems.

• The Problem: Early sensors used oxygen as an electron acceptor, making results dependent on the patient's blood oxygen levels (the "Oxygen Effect") and requiring high voltages that caused interference.
• The Standard Solution (Ferricyanide): Potassium Ferricyanide became the dominant 2nd-generation mediator. It replaced oxygen, allowing for more consistent results, but still required relatively high voltages and relied on diffusional transfer.
• The Advanced Solution (Osmium/Ruthenium): Modern premium strips (e.g., Abbott, Roche) utilize Transition Metal Complexes (specifically Osmium or Ruthenium) often "wired" to the enzyme via polymers.

Key Benefits of Advanced Mediators:

1. Low Potential: Operates at low voltages (<0.2V), preventing the oxidation of interfering drugs like acetaminophen.

2. Speed: Faster electron transfer enables 5-second test times.

3. Stability: "Wired" enzymes prevent chemical leaching and improve shelf-life.