A film that can sense alcohol with your smartphone

Checking the alcohol content of wine, sake, or even your breath could soon be as simple as looking at the color of a thin film through your phone’s camera. A research team in Japan has developed a new kind of alcohol sensor that changes color when it detects ethanol, turning a futuristic concept into a working reality. This innovation goes far beyond convenience. Alcohol, or ethanol (EtOH), is one of the world’s most widely used chemicals. It appears in fuels, disinfectants, medicines, and, of course, beverages. Being able to measure alcohol concentration quickly and accurately is vital for industries from food and drink production to environmental monitoring and healthcare. Traditionally, detecting alcohol requires either specialized laboratory equipment or electronic gas sensors that need external power. But the researchers behind a study published in [Small Science], a journal from Wiley, have developed a clever alternative: a paper-thin film made from a copper-based metal–organic framework (MOF) that visibly changes color in response to alcohol vapors. Even better, the color change can be analyzed with nothing more than a smartphone camera. The work was realized by Yuto Toki, Kenji Okada, Arisa Fukatsu, and Masahide Takahashi from Osaka Metropolitan University, in collaboration with Yuta Tsuji at Kyushu University. Together, they’ve opened up an entirely new way to think about chemical sensing. ### Why alcohol detection? If you’ve ever brewed beer or fermented kombucha, you know how important it is to control alcohol content. Too little, and the product won’t taste right. Too much, and it can be unsafe or spoil regulatory limits. On an industrial scale, precision is even more crucial. Outside of food, alcohol detection has other important roles. Doctors may need to measure blood alcohol levels in patients. Factories must keep track of ethanol emissions for safety and environmental compliance. Breathalyzers are used to check whether drivers are intoxicated. In short, there are countless moments when knowing the exact ethanol concentration, quickly and reliably, can make a big difference. Yet current sensing technologies have drawbacks. Metal-oxide gas sensors are compact and cheap, but they need electricity and aren’t always precise across wide concentration ranges. High-end lab instruments, like spectrometers, give accurate readings but are expensive and not portable. This is where color comes in. A simple color change is one of the most intuitive signals humans can interpret. Think of litmus paper turning red or blue to indicate acidity. A similar idea, called *chromism*, has been explored for alcohol sensing, but until now, no material offered both sensitivity and reversibility across the full range of ethanol concentrations. At the heart of this breakthrough is a material known as a **metal–organic framework** (MOF). MOFs are crystalline structures made by linking metal ions with organic molecules. You can picture them as scaffolds with nanoscale pores, like molecular sponges that can soak up specific gases or liquids. What makes MOFs fascinating is their tunability. By swapping out different metals or organic linkers, scientists can create frameworks with custom pore sizes and chemical properties. Some MOFs can store gases like hydrogen, others can catalyze reactions, and, as shown here, some can change color when molecules slip inside their pores. The Osaka–Kyushu team focused on a specific MOF called **Cu-MOF-74**. Built around copper ions, this framework features open metal sites that readily interact with guest molecules such as water or ethanol. When ethanol enters, the structure’s electronic properties shift, leading to a visible color change. The concept sounds straightforward, but there was a big hurdle. In powdered form, Cu-MOF-74 scatters too much light, making the color change hard to see. The researchers solved this by creating **ultra-thin, transparent films** of the material, which allowed clean, easily visible shifts in color. So how does this film actually work? When exposed to ethanol vapor (or liquid mixtures of ethanol and water), the film changes its hue. At lower ethanol concentrations, it looks more orange; as the concentration rises, it shifts toward brown. These changes are not just subtle laboratory effects, they’re dramatic enough to be detected by an ordinary smartphone camera. Here’s where the team had a brilliant idea. The researchers developed a smartphone app that reads the red–green–blue (RGB) color values from a photo of the film and translates them into alcohol concentrations. The app could successfully measure the alcohol content of commercial beverages like sake, whisky, and rum, and the results matched the labeled percentages. That means you could, in principle, check whether your bottle of wine really contains 13.5% alcohol, or whether your sake matches its listed strength, all with a simple portable test. Even more impressively, **color changes in the film are reversible and repeatable**. The MOF can adsorb and release ethanol molecules over and over again without degrading. In tests, the films retained their performance after at least fifty cycles of alcohol exposure. If you dig deeper into the physics, the color change comes from tiny shifts in the electronic structure of the MOF. When ethanol molecules enter the copper framework, they interact with specific bonds inside the structure, slightly altering their lengths. These changes in turn modify the material’s bandgap, the energy difference that determines how it absorbs light. In simpler terms, the MOF acts like a mood ring for molecules. Different guest molecules tweak its internal structure in different ways, and those tweaks translate into visible colors. The team’s experiments, supported by advanced computer simulations, showed that water, ethanol, and other alcohols like 2-propanol all affected the Cu-MOF-74 framework differently. Ethanol, crucially, produced distinct and measurable color shifts across the entire concentration spectrum. The potential applications are wide-ranging. For instance, in the food and beverage industry, quality control during brewing, winemaking, or distilling could become faster and easier. It also has potential applications in environmental monitoring, where factories could track ethanol emissions without needing complex equipment. In healthcare, breath alcohol tests could be simplified, making portable, inexpensive alternatives to current breathalyzers possible. And finally, with just a film and a smartphone, students or hobbyists could explore chemistry in action, with significant implications for education and citizen science. What makes this work stand out is its combination of **simplicity, portability, and full-range sensitivity**. It doesn’t require power-hungry electronics, expensive spectrometers, or specialized training. The film is small and cheap to produce, and smartphones are already everywhere. This is because the approach overcomes the limitations of older chromism-based sensors, which often suffered from low sensitivity, irreversibility, or only worked at certain concentration ranges. By harnessing the unique properties of Cu-MOF-74, the team has created a truly versatile solution. ### What’s next? While this study represents a proof of concept, there’s plenty of room for future development. The films could be integrated into compact sensor devices or combined with custom apps for specific industries. Researchers could also explore tailoring other MOFs to detect different gases or liquids, imagine a family of color-changing films for everything from carbon dioxide to hazardous pollutants. There’s also potential in consumer applications. A thin sticker on a bottle cap that changes color with alcohol strength? A portable breath test you can use privately before driving? The possibilities are tantalizing. Chemistry doesn’t always have to be hidden in laboratories and complicated instruments. Sometimes, molecules announce their presence with something as simple and human as a shift in color. The research team behind this study has shown that, by harnessing the power of MOFs, we can literally watch chemistry happen, and, with the help of our smartphones, turn those colors into meaningful measurements. Until we will be able to raise a glass and answer the question “how strong is this drink?” by snapping a photo. If you want to learn more, read the original article titled "Solvato/Vapochromism-Based Alcohol Sensing through Metal–Organic Framework Thin Films with Coordinatively Unsaturated Metal Sites" on [Small Science] at . [Small Science]: http://dx.doi.org/10.1002/smsc.202400634

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