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 approximate to 5 mu L of solution with the entire process taking approximate to 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.