High-performance formaldehyde electrochemical sensor utilizing Nafion as solid electrolyte for human exhaled breath detection.

Formaldehyde (HCHO), as a representative biomarker associated with lung cancer screening, plays a key role in distinguishing healthy individuals from those with diseases through its ppb-level concentration differences. Therefore, achieving high sensitivity and low limit of detection (LOD) for specific detection of HCHO is critically important. In this work, a HCHO electrochemical sensor was prepared using a two-step drop-coating method on a flexible planar screen-printed electrode, with 60 % Pt/C-Nafion catalyst as the sensing layer and Nafion as the solid-state electrolyte. At a working potential of 0.5 V, high sensitivity (0.197 μA/ppm), a wide linear response range (HCHO concentration from 500 ppb to 100 ppm) and a low LOD (2.5 ppb) have been achieved for HCHO detection at room temperature. The sensor also exhibits excellent selectivity, consistency and long-term stability (>15 days). Through ultra-low concentration sensing tests of 50-400 ppb HCHO using a fluorine membrane gas bag, the sensor demonstrates good linearity with a sensitivity of 0.8 nA/ppb, which can effectively distinguish between exhaled breath from healthy individuals and simulated lung cancer patients. The appropriate selection of working potential, efficient construction of three-phase boundary (TPB) and excellent electrocatalytic performance of the Pt/C catalyst enable the realization of high-performance HCHO detection. Additionally, the sensor preparation method is simple and cost-effective. Therefore, the proposed Nafion-based HCHO electrochemical sensor is expected to provide a promising sensing platform for lung cancer screening in clinical diagnosis and indoor HCHO concentration monitoring.