Nitrite/nitrate detection in serum based on dual-plate generator–collector currents in a microtrench

A dual-electrode sensor is developed for rapid detection of nitrite/nitrate at micromolar levels in phosphate buffer media and in dilute horse serum without additional sample pre-treatment. A generator–collector configuration is employed so that on one electrode nitrate is reduced to nitrite and on the second electrode nitrite is oxidised back to nitrate. The resulting redox cycle gives rise to a specific and enhanced current signal which is exploited for sensitive and reliable measurement of nitrite/nitrate in the presence of oxygen. The electrode design is based on a dual-plate microtrench (approximately 15µm inter-electrode gap) fabricated from gold-coated glass and with a nano-silver catalyst for the reduction of nitrate. Fine tuning of the phosphate buffer pH is crucial for maximising collector current signals whilst minimising unwanted gold surface oxidation. A limit of detection of 24μM nitrate and a linear concentration range of 200–1400μM is reported for the microtrench sensor in phosphate buffer and dilute horse serum. Relative standard deviations for repeat measurements were in the range 1.8–6.9% (n=3) indicating good repeatability in both aqueous and biological media. Preliminary method validation against the standard chemiluminescence method used in medical laboratories is reported for nitrate analysis in serum. [Display omitted] •Application of a double-electrode for direct detection in serum.•New route to detection of nitrate/nitrite by generator–collector electrochemistry.•Preparation of a microtrench with silver catalyst on the cathode and gold on the anode.•Good repeatability in aqueous and biological media at millimolar concentrations.•Comparison against standard chemiluminescence method.