No abstract

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.

Volatile organic compounds (VOCs) comprises a broad class of small molecules (up to ~300 g/mol) produced by biological and non-biological sources. VOCs play a vital role in an organism’s metabolism during its growth, defense, and reproduction. The well-known 6-pentyl-α-pyrone (6-PP) molecule is an example of a major volatile biosynthesized by Trichoderma atroviride that modulates the expression of PIN auxin-transport proteins in primary roots of Arabidopsis thaliana during their relationship. Their beneficial relation includes lateral root formation, defense induction, and increased plant biomass production. The role of 6-PP has been widely studied due to its relevance in this cross-kingdom relationship. Conventional VOCs measurements are often destructive; samples require further preparation, and the time resolution is low (around hours). Some techniques enable at-line or real-time analyses but are highly selective to defined compounds. Due to these technical constraints, it is difficult to acquire relevant information about the dynamics of VOCs in biological systems. Low-temperature plasma (LTP) ionization allows the analysis of a wide range of VOCs by mass spectrometry (MS). In addition, LTP-MS requires no sample preparation, is solvent-free, and enables the detection of 6-PP faster than conventional analytical methods. Applying static statistical methods such as Principal Component Analysis (PCA) and Discriminant Factorial Analysis (DFA) leads to a loss of information since the biological systems are dynamic. Thus, we applied a time series analysis to find patterns in the signal changes. Our results indicate that the 6-PP signal is constitutively emitted by T. atroviride only; the signal shows high skewness and kurtosis. In A. thaliana grown alone, no signal corresponding to 6-PP is detected above the white noise level. However, during T. atroviride-A. thaliana interaction, the signal performance showed reduced skewness and kurtosis with high autocorrelation. These results suggest that 6-PP is a physiological variable that promotes homeostasis during the plant-fungal relationship. Although the molecular mechanism of this cross-kingdom control is still unknown, our study indicates that 6-PP has to be regulated by A. thaliana during their interaction.