Two-dimensional self-assembled network structure of Co3O4 quantum-dot-decorated ZnO nanobeads for ppb-level acetone sensors

•A high-sensitivity sensor that can detect ppb-level acetone at 250 °C.•Nanomaterial p-n junction 2D-network structure formation for gas sensor.•Self-assembly process for the formation of nanomaterial 2D network structure. A two-dimensional self-assembled network structure of ZnO nanobeads (NBs) decorated with Co3O4 quantum dots (QDs) was fabricated by an alcohol-assisted Langmuir–Blodgett method for a highly sensitive acetone sensor. Owing to the formation of a p–n junction between the Co3O4 QDs and ZnO NBs and the catalytic activity of Co3O4 QDs for acetone oxidation, the operating temperature of the sensor decreased from 350 to 250 °C, and the response to 1 ppm acetone increased from 5.3 to 7.2. The response was 1.5 even to 40 ppb acetone. Furthermore, the sensor was applied to a commercial breath analyzer, and ppb-levels of acetone were successfully detected in the exhalation of an adult.