A Smartphone-Assisted Approach to Formaldehyde Detection Using Diethanolamine-Grafted Carbon Nanoparticles.

Formaldehyde (FA) is a well-known indoor pollutant and human carcinogen, making the development of field-deployable sensors for its monitoring crucial for public safety. Herein, we report a facile strategy to synthesize carbon nanoparticles functionalized with diethanolamine (CNPs-DEA) as FA sensors. The strategic surface functionalization dictates a specific spatial arrangement that is key to efficient and cooperative interaction with the analyte. In water solution, the probe exhibits a LOD of 46 ppb with a binding constant (log β) value of 4.31 ± 0.01. By immobilizing the CNPs on polyamide membranes, we engineered a solid-state strip test integrated with a 3D-printed smartphone readout platform. This setup delivers an ultralow detection threshold (1 ppb) for gaseous FA and, crucially, maintains robust performance under saturated humidity conditions, overcoming a major limitation of conventional carbon-based sensors. The practical utility of the device was validated by quantifying FA in commercial paint samples. Combining operational simplicity, low cost, and high sensitivity, this platform represents a robust early warning tool for air quality monitoring, bridging the gap between sophisticated laboratory instrumentation and accessible real-world applications.