Application of porous metal enrichment probe sampling to single cell analysis using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS)

Anthocyanin in the Vacuole of Red Onion Epidermal Cells Quenches Other Fluorescent Molecules

Peels from the inner epidermis of onion bulbs are a model system in plant cell biology. While the inner epidermis of red onions is characteristically white, small patches of cells sometimes redden, containing vacuolar anthocyanin. This study investigated the spectroscopic properties of these anthocyanic cells. When fluorescent dyes were loaded into the vacuole of onion epidermal cells, the anthocyanic cells showed decreased dye fluorescence. This decrease was observed for fluorescein and carboxyfluorescein that are pumped into the vacuole by anion transporters, for acridine orange which acid loads into the vacuole, and for the fluorescent sugar analogue esculin loaded into the vacuole by sucrose transporters. Similar decreases in carboxyfluorescein fluorescence were observed when dye was loaded into the vacuoles of several other plant species, but decreases were not observed for dyes resident in the tonoplast membrane. As cellular physiology was unaffected in the anthocyanic cells, with cytoplasmic streaming, vacuolar and cytoplasmic pH not being altered, the decreased dye fluorescence from the anthocyanic cells can be attributed to fluorescence quenching. Furthermore, because quenching decreased with increasing temperature. It was concluded, therefore, that vacuolar anthocyanin can statically quench other fluorescent molecules in vivo, an effect previously demonstrated for anthocyanin in vitro.

Quantification of Drug Molecules in Live Single Cells Using the Single-Probe Mass Spectrometry Technique

Analyzing cellular constituents on the single-cell level through mass spectrometry (MS) allows for a wide range of compounds to be studied simultaneously. However, there is a need for quantitative single-cell mass spectrometry (qSCMS) methods to fully characterize drug efficacy from individual cells within cell populations. In this study, qSCMS experiments were carried out using the Single-probe MS technique. The method was successfully used to perform rapid absolute quantifications of the anticancer drug irinotecan in individual mammalian cancer cells under ambient conditions in real time. Traditional liquid chromatography/mass spectrometry (LC/MS) quantifications of irinotecan in cell lysate samples were used to compare the results from Single-probe qSCMS. This technique showcases heterogeneity of drug efficacy on the single-cell level.

Integrated Cell Manipulation Platform Coupled with the Single-probe for Mass Spectrometry Analysis of Drugs and Metabolites in Single Suspension Cells

Single cell mass spectrometry (SCMS) enables sensitive detection and accurate analysis of broad ranges of cellular species on the individual-cell level. The single-probe, a microscale sampling and ionization device, can be coupled with a mass spectrometer for on-line, rapid SCMS analysis of cellular constituents under ambient conditions. Previously, the single-probe SCMS technique was primarily used to measure cells immobilized onto a substrate, limiting the types of cells for studies. In the current study, the single-probe SCMS technology has been integrated with a cell manipulation system, typically used for in vitro fertilization. This integrated cell manipulation and analysis platform uses a cell-selection probe to capture identified individual floating cells and transfer the cells to the single-probe tip for microscale lysis, followed by immediate mass spectrometry analysis. This capture and transfer process removes the cells from the surrounding solution prior to analysis, minimizing the introduction of matrix molecules in the mass spectrometry analysis. This integrated setup is capable of SCMS analysis of targeted patient-isolated cells present in body fluids samples (e.g., urine, blood, saliva, etc.), allowing for potential applications of SCMS analysis to human medicine and disease biology.

Recent advances in single-cell analysis by mass spectrometry

Cells are the most basic structural units that play vital roles in the functioning of living organisms. Analysis of the chemical composition and content of a single cell plays a vital role in ensuring precise investigations of cellular metabolism, and is a crucial aspect of lipidomic and proteomic studies. In addition, structural knowledge provides a better understanding of cell behavior as well as the cellular and subcellular mechanisms. However, single-cell analysis can be very challenging due to the very small size of each cell as well as the large variety and extremely low concentrations of substances found in individual cells. On account of its high sensitivity and selectivity, mass spectrometry holds great promise as an effective technique for single-cell analysis. Numerous mass spectrometric techniques have been developed to elucidate the molecular profiles at the cellular level, including electrospray ionization mass spectrometry (ESI-MS), secondary ion mass spectrometry (SIMS), laser-based mass spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). In this review, the recent advances in single-cell analysis by mass spectrometry are summarized. The strategies of different ionization modes to achieve single-cell analysis are classified and discussed in detail.

Advances in mass spectrometry based single-cell metabolomics

Single cell metabolomics using mass spectrometry can contribute to understanding biological activities in health and disease.