One‐Step Nanoextraction and Ultrafast Microanalysis Based on Nanodroplet Formation in an Evaporating Ternary Liquid Microfilm

Preconcentration is key for detection from an extremely low concentration solution, but requires separation steps from a large volume of samples using extracting solvents. Here, a simple approach is presented for ultrafast and sensitive microanalysis from a tiny volume of aqueous solutions. In this approach, liquid–liquid nanoextraction in an evaporating thin liquid film on a spinning substrate is coupled with quantitative analysis in one step. The approach is exemplified using a liquid mixture comprising a target compound to be analyzed in water, mixed with extractant oil and co‐solvent ethanol. With rapid evaporation of ethanol, nanodroplets of oil form spontaneously in the film. The compounds are highly concentrated by liquid evaporation and meanwhile extracted to nanodroplets. A detection limit of nanomolar to picomolar is demonstrated for fluorescent model compounds in only ≈5 µL of solution with the entire process taking ≈10 s. The combination of nanoextraction and infrared microscopy also enables simultaneous chemical identification. The dynamics of thin film evaporation are revealed using fast imaging. The principle behind this approach is general, providing a powerful technique for fast and sensitive chemical analysis of a vast library of compounds for environment monitoring, national security, early diagnosis, and many other applications. A simple approach based on nanoextraction is developed for ultrafast microanalysis of liquid samples with a tiny volume. The approach combines nanodroplet formation in an evaporating liquid film on a spinning substrate to achieve highly effective concentrating and in situ chemical detection in a single step within 10 s.