# name
Low-cost colorimetric sensor for ppb-level formaldehyde monitoring

# metadata.dc.description.abstract[].value
Formaldehyde is a hazardous indoor pollutant, and low-cost sensors capable of monitoring exposures at partsper-billion (ppb) levels remain scarce. Here, we report a paper-based colorimetric sensor combining a primary amine/pH-indicator ink with an off-the-shelf LED/photodetector module for quantitative detection. Formaldehyde reacts with the amine to form an imine, inducing a localized pH shift and visible color change detected optically. Continuous reaction rate monitoring enables quantitative tracking of formaldehyde concentration. The ink formulation was optimized for sensitivity and saturation time (4.2% aPEG, 4% PEG), while adjustments in film thickness and substrate reflectivity allow performance tailoring for specific applications. Because relative humidity significantly modulates the sensor response through reversible imine hydrolysis, several calibration approaches, considering non-linear and linear dependence with humidity were evaluated. A multivariable linear regression model incorporating formaldehyde concentration, relative humidity, and their interaction term was

selected, explaining 94% of the variance in the sensor signal. After testing the model with simultaneous variations of all dependent variables (a deliberately aggressive validation scenario), a key insight emerged: the time evolution of the system must be incorporated in future models, as accumulated reaction products can introduce systematic deviations. The sensor selectively detected formaldehyde in the 80–600 ppb range with an experimental LoD of 80 ppb and negligible interference from NH₃, NO₂, EtOH, CO, and CO₂. Repeated exposures over seven days yielded 155.6 ± 14.3 ppb for 35 exposures at a nominal 160 ppb concentration (≈7% error). Sensor response was minimally affected by 25–40 ◦C, indicating no thermal compensation is required.

# metadata.dc.relation.ispartof[].value
Sensors and Actuators B-Chemical, 2026, vol. 461

# metadata.dc.rights[].value
cc-by (c) González Gómez, María, et al., 2026

# metadata.dc.source[].value
Articles publicats en revistes (Enginyeria Electrònica i Biomèdica)

# metadata.dc.title[].value
Low-cost colorimetric sensor for ppb-level formaldehyde monitoring