Direct ionization of biological tissue for mass spectrometric analysis

Abstract

Analysis of biological tissue at a molecular level is of great importance in biological, medical and clinical studies. In this manuscript, we report that both plant and animal tissues can be directly ionized and analyzed by mass spectrometry under ambient conditions. By adding some solvents and applying a high voltage, spray ionization can be induced at the tip of biological tissue and a mass spectrum can be observed. Various plant and animal tissues have been tested and compounds such as lipids, alkaloids, glucosides, lignans, pharmaceuticals and proteins could be detected in the spectra. This new technique provides a simple and rapid method for tissue analysis and allows observation of compounds that cannot be detected by other ionization techniques.

Analytical Properties of Solid-substrate Electrospray Ionization Mass Spectrometry

“…For comparison, the extract was directly analyzed with the extract solution loaded to the sharp tip-end of the wooden tips. Both polar and low-polar compounds and compounds such as monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) were detected in this case (Figure 2c), covering most components observed by LC-MS [15]. These components, however, could not be detected by analysis of the extract using nano-ESI [15].…”

“…Both polar and low-polar compounds and compounds such as monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) were detected in this case (Figure 2c), covering most components observed by LC-MS [15]. These components, however, could not be detected by analysis of the extract using nano-ESI [15]. These results indicated that the solid-substrate ESI had lower signal suppression and could provide a more complete profile of the sample.…”

“…Use of noncapillary emitters avoids the problem of clogging that could occur in capillary-based ESI and allows much easier sampling. Particularly, analysis of samples on surfaces or in difficult-to-access corners could be greatly facilitated by collecting sample using paper [12,13] or wooden tips [14] followed by paper spray or wooden tip ESI-MS. More recently, noncapillary ESI techniques have been further extended to direct mass spectrometric analysis of biological tissue [15][16][17][18].…”

“…With~2 μL of the cream, the signals lasted for about 15 min. Metal needles can also be used to hold soft animal tissue for direct ionization analysis [15]. Direct ionization could also be achieved with samples that could form tips to allow for solid substrate ESI-MS analysis.…”

“…This provides a simple and rapid method for analysis of substances on leaf surface. Leaves could also be cut into V-shape [15,16] to allow their endogenous compounds to be analyzed using the solidsubstrate ESI method.…”