Collection-Free Express H ₂ O ₂ Detection in Breath Aerosol through Its Capillary Condensation Directly onto the Sensor Surface

We report on express hydrogen peroxide detection in breath aerosol, omitting the stage of its intermediate collection. Express detection is possible through aerosol capillary condensation by graphene oxide (GO) and hygroscopic salt (KF) layers onto the sensor surface based on Prussian Blue (PB) being the most advantageous electrocatalyst for H 2 O 2 reduction. The optimal composition of the condensing membrane (≥30 μg·cm −2 of GO; ∼6 μmol·cm −2 of KF) ensures sufficient PB electroactivity with the redox-peak separation below 100 mV already after 5 s from the start of aerosol passage (80 mL·s −1 ). Express aerosol analysis is performed by short-circuiting the working and Ag electrodes, resulting in a current peak generated within 2 s. Its height is proportional to the H 2 O 2 content in the aerosol liquid phase in the range from 0.3 to 10 µM. Similar to the standard method based on preliminary aerosol collection, the collection-free direct H 2 O 2 detection in breath aerosol allows distinguishing pulmonary oxidative stress of patients suffering from inflammatory diseases and that of smokers. The express analysis of breath aerosol on the basis of its capillary condensation would obviously open a new area in non-invasive diagnostics of pulmonary disorders.