Principle of the routine glucose biosensor

In standard home glucometers:

• The enzyme glucose oxidase oxidizes β‑D‑glucose to gluconolactone (which forms gluconic acid) and simultaneously reduces oxygen to hydrogen peroxide:
  Glucose + O₂ → gluconic acid + H₂O₂.

• The sensor’s electrode then measures the current generated by oxidation of H₂O₂, which is directly proportional to its concentration, and hence to the original blood glucose concentration.
  So, what is actually “sensed” electrochemically is mostly hydrogen peroxide, not glucose itself.

Option-wise explanation

1. Glucose

• Glucose is the analyte of interest, but in routine first‑generation biosensors it is not measured directly; it is converted enzymatically, and a product/by‑product is detected instead.

2. Oxygen

• Some early designs could estimate glucose by the decrease in oxygen concentration during the reaction, but this is less accurate because oxygen levels can vary in the sample.

• Modern routine glucometers mainly track H₂O₂, not oxygen.

3. δ‑Gluconolactone

• This is the immediate product of glucose oxidation before forming gluconic acid.

• It is not typically monitored electrochemically in commercial strips.

4. H₂O₂ – correct

• Hydrogen peroxide is produced stoichiometrically with glucose oxidation and is easily oxidized at an electrode, giving a strong, quantifiable current.

• Routine glucose biosensors therefore estimate blood glucose by sensing the concentration of H₂O₂, making option 4 correct.