Dual electrochemical microsensor for simultaneous measurements of nitric oxide and oxygen: Fabrication and characterization

A planar-type amperometric dual microsensor was developed for the simultaneous measurement of the nitric oxide (NO) and oxygen (O2) concentrations. The sensor (overall diameter = ∼500 μm) consisted of a dual working electrode (WE) containing two platinized platinum microdisks (25 μm diameter, WE1, WE2, distance between two disks > ∼330 μm) and a Ag/AgCl wire reference electrode covered with an expanded poly(tetrafluoroethylene) gas-permeable membrane. The differentiation and concurrent measurements of NO and O2 were obtained successfully using two sensing WEs with different applied potentials (+0.75 V for WE1 and −0.4 V for WE2). Cross-talk between WE1 and WE2 was eliminated with an optimized internal solution composition. Linear dynamic range, selectivity, sensitivity, detection limit (<5 nM for NO; <500 nM for O2), and stability (>50 h) were evaluated.