Bismuth-Based, Disposable Sensor for the Detection of Hydrogen Sulfide Gas

A new sensor for the detection of hydrogen sulfide (H₂S) gas has been developed to replace commercial lead­(II) acetate-based test papers. The new sensor is a wet, porous, paper-like substrate coated with Bi­(OH)₃ or its alkaline derivatives at pH 11. In contrast to the neurotoxic lead­(II) acetate, bismuth is used due to its nontoxic properties, as Bi­(III) has been a reagent in medications such as Pepto-Bismol. The reaction between H₂S gas and the current sensor produces a visible color change from white to yellow/brown, and the sensor responds to ≥30 ppb H₂S in a total volume of 1.35 L of gas, a typical volume of human breath. The alkaline, wet coating helps the trapping of acidic H₂S gas and its reaction with Bi­(III) species, forming colored Bi₂S₃. The sensor is suitable for testing human bad breath and is at least 2 orders of magnitude more sensitive than a commercial H₂S test paper based on Pb­(II)­(acetate)₂. The small volume of 1.35-L H₂S is important, as the commercial Pb­(II)­(acetate)₂-based paper requires large volumes of 5 ppm H₂S gas. The new sensor reported here is inexpensive, disposable, safe, and user-friendly. A simple, laboratory setup for generating small volumes of ppb–ppm of H₂S gas is also reported