A Paper-Based Ultrasensitive Optical Sensor for the Selective Detection of H₂S Vapors

• Main Authors: Alejandro P. Vargas, Francisco Gámez, Javier Roales, Tânia Lopes-Costa, José M. Pedrosa
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Chemosensors
• Subjects: optical gas sensor; chemical sensors; toxic gases; colorimetric probes
• Online Access: https://www.mdpi.com/2227-9040/9/2/40

A selective and inexpensive chemical paper-based sensor for the detection of gaseous H₂S is presented. The triggering of the sensing mechanism is based on an arene-derivative dye which undergoes specific reactions in the presence of H₂S, allowing for colorimetric analysis. The dye is embedded into a porous cellulose matrix. We passively exposed the paper strips to H₂S generated in situ, while the absorbance was monitored via an optic fiber connected to a spectrophotometer. The kinetics of the emerging absorbance at 534 nm constitute the sensor response and maintain a very stable calibration signal in both concentration and time dimensions for quantitative applications. The time and concentration dependence of the calibration function allows the extraction of unusual analytical information that expands the potential comparability with other sensors in the literature, as the limit of detection admissible within a given exposure time. The use of this specific reaction ensures a very high selectivity against saturated vapors of primary interferents and typical volatile compounds, including alkanethiols. The specific performance of the proposed sensor was explicitly compared with other colorimetric alternatives, including standard lead acetate strips. Additionally, the use of a smartphone camera to follow the color change in the sensing reaction was also tested. With this straightforward method, also affordable for miniature photodiode devices, a limit of detection below the ppm scale was reached in both colorimetric approaches.