 Although polymer-based sensors are in many ways easier to fabricate than their more rigid inorganic counterparts, the typical recipe for building this type of sensor still calls for highly specialized equipment and can be rather costly and time-consuming. But researchers recently showed that all you really need is a pair of tweezers, a beaker, and less than one minute of prep time. Polymer sensors are everywhere. They're used to measure variations in pH levels and humidity and detect certain gases. Part of the reason why polymer sensors have become so widespread is that they're easy to process, which makes them cost-effective. In the case of polymer sensors that can detect oxygen, for example, a polymer solution is typically mixed with an oxygen-sensing chromophore, a fluorescent molecule whose emission of light is altered by the presence of oxygen. This solution is then spin-coded onto a solid substrate, typically an inorganic material such as glass or a second polymer, to produce a thin sensing film. This film can take the form of a flexible patch and can be used to monitor respiration kinetics in a bioreactor or placed on food packaging to signal when a product has gone bad. Despite their easy fabrication, however, these flat optical sensors still require multiple processing steps, dedicated instrumentation, and frequent replacement. To overcome these shortcomings, the researchers in this study used a substantially faster and simpler fabrication process called Solvent Immersion Imprint Lithography, or SIIL. Unlike the typical mix-and-coat procedure, in SIIL, chromophore molecules are simply absorbed into a polymer substrate. This is achieved by immersing the substrate in a solvent containing the fluorescent molecules. The solvent relaxes the polymer chains near the surface of the substrate, which helps the chromophores diffuse into the material. The substrate essentially soaks up the oxygen-sensitive molecules like a sponge soaks up water. As the solvent is dried out of the polymer, the strong binding between the solvent molecules and the chromophore molecules concentrates the chromophores near the surface of the polymer. The entire process takes less than a minute to complete, and the result is a planar sensor that is able to respond to changes in the concentration of molecular oxygen. What's more is that the concentration of the chromophores and the depth to which they penetrate the polymer can be adjusted by modifying the chromophore concentration in solution and the immersion time respectively. Both allow the sensitivity and dynamic range of the sensor to be controlled. In fact, the sensor shows one of the highest dynamic ranges recorded for its type. Its potential to vastly accelerate the processing of polymer materials without the need for complicated instrumentation makes SIIL a promising method for sensing applications in the life and energy sciences. And because there's no need to coat a substrate in the traditional sense, SIIL-based sensors are immune to the peeling that plagues thin film sensors under harsh environments, such as nuclear reactors. The researchers therefore expect that SIIL can be adapted to a whole suite of polymer materials and sensing applications, including radiation detection.