Low-temperature plasma (LTP) ionization represents an emerging technology in ambient mass spectrometry. LTP enables the solvent-free direct detection of a broad range of molecules and mass spectrometry imaging (MSI). The low energy consumption and modest technical requirements of these ion sources favors their employment in mobile applications and as a means to upgrade existing mass analyzers. However, the broad adoption of LTP is hindered by the lack of commercial devices, and constructing personal devices is tricky. Improper setup can result in equipment malfunction or may cause serious damage to instruments due to strong electromagnetic fields or arcing. With this in mind, we developed a reproducible LTP probe, which is designed exclusively from commercial and 3D printed components. The plasma jet generated by the device has a diameter of about 200 μm, which is satisfactory for the ambient imaging of macroscopic samples. We coupled the 3D-LTP probe to an ion trap analyzer and demonstrated the functionality of the ion source by detecting organic and chemical compounds from pure reference standards, biological substances, and pharmaceutical samples. Molecules were primarily detected in their protonated form or as water/ammonium adducts. The identification of compounds was possible by standard collision-induced dissociation (CID) fragmentation spectra. The files necessary to reproduce the 3D parts are available from the project page ( http://lababi.bioprocess.org/index.php/3d-ltp ) under a dual license model, which permits reproduction of the probe and further community-driven development for noncommercial use ("peer production"). Our reproducible probe design thus contributes to a facilitated adaption and evolution of low-temperature plasma technologies in analytical chemistry.

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Even populations of clonal cells are heterogeneous, which requires high-throughput analysis methods with singlecell sensitivity.H ere,w ep ropose ar apid, label-free single-cell analytical method based on active capillary dielectric barrier discharge ionization mass spectrometry,w hich can analyze multiple metabolites in single cells at arate of 38 cells/minute. Multiple cell types (HEK-293T,P ANC-1, CFPAC-1, H6c7, HeLa and iBAs) were discriminated successfully.W ef ound evidence for abnormal lipid metabolism in pancreatic cancer cells.W ea lso analyzed gene expression in ac ancer genome atlas dataset and found that the mRNAl evel of ac ritical enzyme of lipid synthesis (ATP citrate lyase,A CLY) was upregulated in human pancreatic ductal adenocarcinoma (PDAC). Moreover,b oth an ACLY chemical inhibitor and asiRNAapproachtargeting ACLY could suppress the viability of PDAC cells.Asignificant reduction in lipid content in treated cells indicates that ACLY could be apotential target for treating pancreatic cancer.

The presented low-temperature plasma probe allows the fine-tuning of ionization and desorption parameters, according to the target molecules. Possible applications include: (1) The ambient ionization and desorption of organic compounds with different volatility and (2) The direct analysis of food products such as roasted coffee beans.

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