In Situ Pressure Probe Sampling and UV-MALDI MS for Profiling Metabolites in Living Single Cells

In this work we describe the use of a combination of a cell pressure probe and a UV-matrix-assisted laser desorption/ionization time of flight (UV-MALDI-TOF) mass spectrometer for the in situ picoliter sampling and shotgun metabolite profiling of living single cells of plants. In addition to quantifiable sampling, the pressure probe has some unique features which differentiate it from other single-cell analytical tools. Cell wall and plasma membrane properties and water relations of in situ living single cells can be analyzed before sampling the cell sap. In addition, the fully-controlled sampling of cells located at different depths in plant tissues, measurement of the sample volume, and the addition of internal standards are facilitated by the pressure probe. Using a variety of organic compounds and nanoparticles as UV-MALDI matrices, metabolites from neutral carbohydrates to amino acids and other metabolites can be detected through UV-MALDI-TOF mass spectrometry analyses of picoliter-sized, single-cell samples.