Harnessing acoustic levitation for a complete “lab-in-a-droplet” platform: merging in stillo sample preparation with direct mass spectrometry analysis

The goal of this funding application is the development of a complete lab-in-a-droplet analytical workflow – integrating sample handling and preparation – for biological samples within the confined space of a single acoustically levitated microdroplet and mass spectrometry. A single airborne droplet offers unique advantages in chemical applications, such as significantly reduced sample requirements, low reagent consumption and minimized risk of contamination during analysis. The unique properties of microdroplets also provide conditions that allow important processes such as mixing or chemical reactions to be performed at highly accelerated rates in comparison to in vitro reactions in regular vessels. At the same time, a microdroplet of a few microliters remains fully compatible with established analytical mass spectrometry assays. Whole acoustically levitated droplets have previously been used for direct spectroscopic and mass spectrometric measurements in simple solvent-based systems, there is an almost complete lack of experimental investigations of in stillo sample preparation techniques for complex biological samples such as blood serum, which require sample preparation. The primary aim here is therefore to reproduce established analytical benchtop workflows in a single microdroplet; that is, sample preparation, separation and mass spectrometric detection steps will be conducted in the confined environment of a single acoustically levitated droplet, with all steps performed sequentially within this droplet in a single-axis levitator, while benefiting from the above described advantages of small sample size, increased speed and strongly reduced exposure to interferences. Specifically, we will develop techniques for liquid/liquid extraction, solid-phase extraction, protein precipitation and chemical derivatization, which will be performed from acoustically-levitated microliter-sized biological samples. The resulting sample extract will be directly interrogated by mass spectrometry measurements for a complete analytical workflow. Applications include drug and vitamin analysis from blood serum, as well as environmental contaminants from water samples.