Fabrication of patterned paper-based sensors for highly efficient formaldehyde detection

• Formaldehyde paper-based sensors (PFASs) were developed using a commercial inkjet printer, with optimized printed pattern geometry to enhance gas–reagent interaction. • PFASs were fabricated on filter paper coated with a reactive solution containing thymol blue (TB), bromophenol blue (BPB), and hydroxylamine sulfate, with the TB:BPB ratio optimized for improved sensitivity and selectivity. • Achieved a practical detection limit (PDL) of 1 ppm (naked eye) and an instrumental detection limit (IDL) of 0.01 ppm (colorimetry), with 1.63 × faster response than the best-performing line pattern. • Selectivity tests confirmed negligible response to methanol and other VOCs , and field validation in an industrial casting environment demonstrated detection consistent with a commercial FA detector (1.44 ppm). • Low-cost, reproducible fabrication ( n = 5 ) using filter paper compatible with inkjet printing enables scalable production for real-world FA monitoring. Paper-based sensors are widely used in formaldehyde (FA) sensing in various studies. The development of paper-based sensors with high accuracy and rapid response is important for FA detection. In this study, paper-based FA sensors (PFASs) were developed using a commercial inkjet printer, with filter paper as a substrate. The substrate was coated with a reactive solution containing two pH indicators: thymol blue (TB) and bromophenol blue (BPB), and hydroxylamine sulfate. To evaluate the performance of PFASs, the intensity of the color change caused by FA vapor was detected via colorimetry and optimized with respect to the TB:BPB ratio of the solution and the pattern formation during printing. The optimum TB:BPB ratio was 10:1. The response time decreased as the pattern line width decreased and the pore size increased, and check patterns showed a faster response than those of regularly spaced lines. The sensor was tested in an environment with a relative humidity of 50 ± 5% at room temperature to ensure consistent experimental conditions, minimizing any potential interference from external factors. The color change of the sensor was visibly noticeable for FA concentrations above 1 ppm. Thus, the proposed technique shows great promise for rapid, high-precision FA detection.