Methods to Study Single Cells, Cell Membranes, Single Vesicles, and Exocytosis

Focusing on the neuronal process of exocytosis, the Ewing group has pioneered small-volume chemical measurements at single cells, electrochemical detection for capillary electrophoresis, novel approaches for electrochemical imaging of single cells, and new electrochemical strategies to separate individual nanometer vesicles from cells and quantify their contents. The group also pioneered, in collaboration with the Winograd group, many methods for the development and application of mass spectrometry imaging for subcellular and neurochemical analysis.

In the last 5 years, the team has developed new approaches for electrochemical imaging of single cells with complementary chemical imaging with nanometer spatial resolution and we have developed and applied mass spectrometry imaging at the submicrometer level to build on our earlier work (Science 2004 and PNAS 2010)1,2 to understand domains in cell membranes. In the last 2 years we have had incredible success (best of my career) and: (i) developed a new method to measure the contents of vesicles (JACS, 2015; IF 13),3 (ii) developed SIMS imaging of the fly brain to demonstrate that the drug methylphenidate alters the lipid composition (Analyt Chem, 2015; IF 5.8),4 (iii) measured vesicle contents in situ in live cells with a nanoelectrode in a single cell (Angew Chem, 2015; IF 11.7),5 (iv) measured single exocytosis events from varicosities in the fly using optogenetic stimulation (Angew Chem, 2015),6 shown that excited fluorophores in vesicle membranes generate oxidative stress which in turns leads to electroporation and pore opening in electrochemical cytometry (Angew Chem, 2016),7 (v) applied cisplatin to cells and observed the changes in vesicle content and release to propose a mechanism for the cognitive changes in the “chemobrain” observed in cancer patients (Angew Chem, 2016; and back cover: doi/10.1002/anie.201605032/epdf)8 (vi) used the NanoSIMS to measure and image the transmitter dopamine inside a single nanometer vesicle (ACS Nano 2017: IF 13.3),9 and (vii) discovered that zinc changes vesicle content and the fraction released in exocytosis possibly providing a mechanism to explain how zinc affects learning (Angew Chem, 2017 and front cover).10 The intracellular vesicle impact electrochemical cytometry method we have developed allows us to directly compare the contents of vesicles and the material released in the same system and has revolutionized our work in the last year! Our combined work on open and closed exocytosis was recently published in Quarterly Reviews in Biophysics (2016; IF 7.2)11 and the work to understand electrochemical cytometry of vesicles we reviewed in Accounts of Chem Research (2016; IF 22).12

In addition to the work described above, the group has built a unique mass spectrometry imaging laboratory, second to none in SIMS imaging with an IonTof V instrument, Ionoptika J105 3D Chemical Imager, an AB Sciex Qstar equipped with a C60 ion gun, a Bruker Ultraflextreme MALDI instrument, and now the Cameca NanoSIMS (added last year).

Some Current Research Directions

  • Vesicle impact electrochemical cytometry (VIEC). We are working to examine the mechanism of vesicle opening in VIEC and determine the role of lipids in this mechanism, which could help us understand the effect of lipids on pore opening in exocytosis.
  • New methods for vesicle impact electrochemical cytometry (VIEC). Here we propose new nano fabricated approaches for VIEC, one for high throughput vesicle analysis, and the other to quantify substance in the protein dense core of a single vesicle.
  • Intracellular vesicle impact electrochemical cytometry. We plan to develop new approaches with intracellular vesicle impact electrochemical cytometry (IVIEC) combined with amperometric measurements of exocytosis to measure the fraction of vesicular messenger released and, importantly, we will use these platforms to examine and quantify how lipids (and zinc, which is correlated with learning in mammals) affect the fraction of messenger released during exocytosis, an important step in development of methods to explore the effect of lipids on plasticity.
  • Lipids in signaling plasticity, nanoimaging. We plan to develop methodological paradigms to examine first cell models and then later simple animal models to examine the chemistry associated with dynamic changes in exocytosis. We also plan to examine these cell and animal models using nano mass spectrometry and optical imaging methods.
  • Vesicle structure/function: NanoSIMS combined with IVIEC. We propose to apply our new combined technology with 1) the NanoSIMS, probing to 40 nm spatial resolution and imaging the substructure of vesicles with 2) dynamic amperometric detection of exocytotic release and IVIEC of vesicle content in cells.
  • Drugs, zinc, lipids, and learning/memory. We interested to examine the effects of cognition-enhancing drugs like methylphenidate, modafinil, cocaine (and possibly zinc or lipids in the diet, or glutamate receptor antagonists; e.g. MK-801, CNQX) on the amount and distribution of lipids in the brain, in the active zone of neurons, and in vesicles, as well as the fraction of transmitter released in each exocytosis event, and the level of zinc in vesicles.
  • Model of effectors for short-term memory. Our plan is to assemble the measurements above into a model that will show the simplest chemical steps in the initiation of synaptic plasticity and from there the strengthening to a short-term enhancement otherwise considered short-term memory.


  1. Ostrowski, S. G., et al. Mass Spectrometric Imaging of Highly Curved Membranes During Tetrahymena Mating. Science, 305 (2004) 71-73.
  2. E. Kurczy, et al. Mass Spectrometry Imaging of Mating Tetrahymena: Changes in Cell Morphology Regulate Lipid Domain Formation. Proc. Natl Acad Sci USA, 107 (2010) 2751-2756.
  3. Dunevall, J. et al. Characterizing the catecholamine content of single mammalian vesicles by collision-adsorption events at an electrode. J Am Chem Soc, 137 (2015) 4344-4346.
  4. Phan, N. T. N., Fletcher, J. S., Ewing, A. G. Lipid Structural Effects of Oral Administration of Methylphenidate in Drosophila Brain by Secondary Ion Mass Spectrometry Imaging
 Anal Chem, 87 (2015) 4063-4071.
  5. Li, X., et al., A. G. Quantitative Measurement of Transmitters in Individual Vesicles in the Cytoplasm of Single Cells with Nanotip Electrodes. Angew Chem Int Ed, 54 (2015) 11978-11982.
  6. Majdi, S. et al. Electrochemical Measurements of Optogenetically Stimulated Quantal Amine Release from Single Nerve Cell Varicosities in Drosophila Larvae. Angew Chem Int Ed, 54 (2015) 13609-13612.
  7. Najafinobar, N. et al. Excited Fluorophores Enhance the Opening of Vesicles at Electrode Surfaces in Vesicle Electrochemical Cytometry. Angew Chem Int Ed, 55 (2016) 15081-15085.
  8. Li, X., Dunevall, J. & Ewing, A. G. Using Single-Cell Amperometry to Reveal How Cisplatin Treatment Modulates the Release of Catecholamine Transmitters during Exocytosis. Angew Chem Int Ed, 55 (2016) 9041-9044.
  9. Lovric, J. et al. Nano Secondary Ion Mass Spectrometry Imaging of Dopamine Distribution Across Nanometer Vesicles. ACS Nano, (2017) doi:10.1021/acsnano.6b07233.
  10. Ren, L. et al. Zinc regulates chemical transmitter storage in nanometer vesicles and exocytosis dynamics measured by amperometry. Angew Chem Int Ed (in press).
  11. Ren, L. et al. The Evidence for Open and Closed Exocytosis as the Primary Release Mechanism. Q Rev Biophys, 49 (2016) doi:10.1017/S0033583516000081.
  12. Li, X., Dunevall, J., Ewing, A. G. Quantitative Chemical Measurements of Vesicular Transmitters with Electrochemical Cytometry. Acc Chem Res, 49 (2016) 2347-2354.