Molecular analysis at cellular and subcellular levels, whether on selected molecules or at the metabolomics scale, is still a challenge now. Here we propose a method based on probe ESI mass spectrometry (PESI-MS) for single cell analysis. Detection of metabolites at cellular and subcellular levels was successfully achieved. In our work, tungsten probes with a tip diameter of about 1 μm were directly inserted into live cells to enrich metabolites. Then the enriched metabolites were directly desorbed/ionized from the tip of the probe for mass spectrometry (MS) detection. The direct desorption/ionization of the enriched metabolites from the tip of the probe greatly improved the sensitivity by a factor of about 30 fold compared to those methods that eluted the enriched analytes into a liquid phase for subsequent MS detection. We applied the PESI-MS to the detection of metabolites in single Allium cepa cells. Different kinds of metabolites, including 6 fructans, 4 lipids, and 8 flavone derivatives in single cells, have been successfully detected. Significant metabolite diversity was observed among different cells types of A. cepa bulb and different subcellular compartments of the same cell. We found that the inner epidermal cells had about 20 fold more fructans than the outer epidermal cells, while the outer epidermal cells had more lipids. We expected that PESI-MS might be a candidate in the future studies of single cell "omics".

Matrix unloaded: By changing from fixed-voltage (left) to step-voltage nanoelectrospray (right), the mass-spectrometric analysis of small-volume physiological samples is possible. Separation and ionization are achieved in one process, which avoids sample loss and dilution and prevents interference by the matrix. The result is high sensitivity even for samples at the nanoliter level.

Integrating droplet-based microfluidics with mass spectrometry is essential to high-throughput and multiple analysis of single cells. Nevertheless, matrix effects such as the interference of culture medium and intracellular components influence the sensitivity and the accuracy of results in single-cell analysis. To resolve this problem, we developed a method that integrated droplet-based microextraction with single-cell mass spectrometry. Specific extraction solvent was used to selectively obtain intracellular components of interest and remove interference of other components. Using this method, UDP-Glc-NAc, GSH, GSSG, AMP, ADP and ATP were successfully detected in single MCF-7 cells. We also applied the method to study the change of unicellular metabolites in the biological process of dysfunctional oxidative phosphorylation. The method could not only realize matrix-free, selective and sensitive detection of metabolites in single cells, but also have the capability for reliable and high-throughput single-cell analysis.

Mass spectrometry (MS) is one of the most widely used analytical techniques in many fields. Recent developments in chemical and biological researches have drawn much attention to the measurement of substances with low abundances in samples. Continuous efforts have been made consequently to further improve the sensitivity of MS. Modifications on the mass analyzers of mass spectrometers offer a direct, universal and practical way to obtain higher sensitivity. This review provides a comprehensive overview of the latest developments in mass analyzers for the improvement of mass spectrometers’ sensitivity, including quadrupole, ion trap, time-of-flight (TOF) and Fourier transform ion cyclotron (FT-ICR), as well as different combinations of these mass analyzers. The advantages and limitations of different mass analyzers and their combinations are compared and discussed. This review provides guidance to the selection of suitable mass spectrometers in chemical and biological analytical applications. It is also beneficial to the development of novel mass spectrometers.

Sensitive detection of biomolecules in small-volume samples by mass spectrometry is, in many cases, challenging because of the use of buffers to maintain the biological activities of proteins and cells. Here, we report a highly effective desalting method for picoliter samples. It was based on the spontaneous separation of biomolecules from salts during crystallization of the salts. After desalting, the biomolecules were deposited in the tip of the quartz pipet because of the evaporation of the solvent. Subsequent detection of the separated biomolecules was achieved using solvent assisted electric field induced desorption/ionization (SAEFIDI) coupled with mass spectrometry. It allowed for direct desorption/ionization of the biomolecules in situ from the tip of the pipet. The organic component in the assistant solvent inhibited the desorption/ionization of salts, thus assured successful detection of biomolecules. Proteins and peptides down to 50 amol were successfully detected using our method even if there were 3 × 10(5) folds more amount of salts in the sample. The concentration and ion species of the salts had little influence on the detection results.

Selective activation of benzene has been mainly limited to the C-H activation. Simple replacement of one carbon in benzene with another atom remains unresolved due to the high dissociation energy. Herein, we demonstrate a direct breakage of the particularly strong C = C bond in benzene through ion-molecule reaction in a low-temperature plasma, in which one carbon atom was replaced by one atomic nitrogen with the formation of pyridine. The mechanism for the formation of pyridine from benzene has been proposed based on the extensive investigation with tandem mass spectrometry. The reaction pathway also works to other aromatics such as toluene and o-xylene. This finding provides a new avenue for selective conversion of aromatics into nitrogen-containing compounds.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Abstract. Endometriosis is a prevalent and complex gynecological disease which affects 10% of women of reproductive age. Certain studies have suggested that a substantial number of microRNAs (miRNAs or miRs) are aberrantly or differentially expressed in the ectopic endometrium. To date, to the best of our knowlewdge, there is no report available on the role of miR-29 in the endometrium. In this study, we investigated the expression of the miR-29 family in the endometrium samples from women without endometriosis, as well as in paired ectopic and eutopic endometrium samples by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The results revealed that miR-29c was differentially expressed in the paired eutopic and ectopic endometrium samples. In addition, c-Jun was differentially expressed in the ectopic and eutopic endometrial tissues as determined by western blot analysis. Furthermore, the role of miR-29c in endometrial cell proliferation, invasion and apoptosis was examined in vitro. The results revealed that miR-29c exerted its effects on endometrial cells by suppressing cell proliferation and invasion, as well as promoting cell apoptosis. Furthermore, it was found that c-Jun was a novel target of miR-29c, and c-Jun reversed the effects of miR-29c on the proliferation, invasion and apoptosis of endometrial cells. To the best of our knowledge, this study is the first to identify miR-29c as a suppressor of endometriosis. Taken together, our results suggest that miR-29c exerts its effects on endometrial cell proliferation, apoptosis and invasion by inhibiting the expression of c-Jun. Our data may provide a novel potential therapeutic target for the treatment of endometriosis.