Humans have long relied on animals to sense chemicals in the air—from dogs in search and rescue efforts to canaries in coal mines to warn against dangerous gasses. Now, a study demonstrates that a plant, specifically a common moss, can similarly serve as an environmental sensor and alert system.
Plants, as they exchange carbon dioxide for oxygen, “breathe” in the atmosphere around them and take in numerous other chemicals. Researchers, led by Xingcai Qin and Nongjian Tao of Nanjing University in China, tested Atrichum undulatum—often called big star moss because of its star-shaped leaves—to see how it responded when exposed to sulfur dioxide, a gas emitted by the burning of fossil fuels that forms acid rain and can damage human lungs.
The researchers used an inexpensive webcam to monitor the moss’s response to various levels of sulfur dioxide. At higher, hazardous gas levels, the plant’s leaves changed from their usual healthy green to a sickly yellow, due to sulfur dioxide lowering the leaves’ pH, thereby altering the chemical composition of chlorophyll. Sulfur dioxide exposure also caused the moss’s leaves to curl and shrink. The color change and shape were detectable by image-scanning computer algorithms in as few as ten seconds post-exposure—orders of magnitude more rapid than the several hours that researchers had initially expected.
Unlike conventional, manufactured sensors that must be replaced or reset after a detection event, the moss can naturally return itself to a baseline state by continuously regenerating chlorophyll. Other benefits of leveraging moss as an environmental sensor are its low cost and ready availability. “We used wild moss from the field without further preparation, except to keep high humidity,” said Qin.
Using living material for such purposes does pose some drawbacks: the moss needs to be kept alive, which limits portability. Moss monitors would be better-suited in fixed places, such as homes, roadsides, and factories. The researchers envision basic webcams, traffic cameras, and drone cameras keeping watch over moss installations in such locales. They also speculate that moss could sniff out other potentially hurtful gases, such as hydrogen chloride and ammonia, both of which can cause irritation, burning, and severe injury to the respiratory tract. (Analytical Chemistry)