Surface-Coated Acupuncture Needles as Solid-Phase Microextraction Probes for In Vivo Analysis of Bioactive Molecules in Living Plants by Mass Spectrometry

In this work, we report the coupling of solid-phase microextraction (SPME) enabled by surface-coated acupuncture needles with nano-electrospray mass spectrometry (nanoESI-MS) for the analysis of bioactive molecules in living plants. The needle tip was oxidized by a mixture of nitric acid and hydrogen peroxide solution and then subject to surface coating via carbonization of paraffin. A combination of oxidation and surface coating resulted in a thin coating of carbon film, whereby the significantly increased surface area promoted both analyte enrichment and ionization for MS analysis. The analytical performances were evaluated through the characterization of small molecules, peptides and proteins. Compared with conventional nanoESI, our new strategy of employing surface-coated needles had a high salt tolerance. The streamlined experimental workflow could be completed within one minute. The linear dynamic ranges for L-histidine and L-lysine, as two representatives, were over two orders of magnitude with a limit of detection (LOD) of 3.0~5.0 ng/mL. A mark is made on the needle at 2 mm from the tip, the needle is then kept in the sample for 30 s. In vivo sampling and identification of α-tomatine and organic acids from the stem of a living tomato plant were demonstrated as a practical application, while the physiological activities of the plant were not disrupted due to the minimally invasive sampling. We anticipate that the developed strategy may be of potential use for real-time clinical and other on-site analyses.

Laserspray and matrix-assisted ionization inlet coupled to high-field FT-ICR mass spectrometry for peptide and protein analysis

We present the first coupling of laser spray ionization inlet (LSII) and matrix assisted ionization inlet (MAII) to high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for generation of electrospray-like ions to take advantage of increased sensitivity, mass range, and mass resolving power afforded by multiple charging. We apply the technique to top-down protein analysis and characterization of metalloproteins. We also present a novel method for generation of multiply-charged copper-peptide complexes with varying degrees of copper adduction by LSII. We show an application of the generated copper-peptide complexes for protein charge state and molecular weight determination, particularly useful for an instrument such as a linear ion trap mass analyzer.

Electrospray ionization using wooden tips

Electrospray ionization (ESI) is a mass spectrometric technique widely used in various fields including chemistry, biology, medicine, pharmaceutical industry, clinical assessment, and forensic science. In this study, we report a simple and economical ESI-mass spectrometry (MS) technique, which makes use of disposable wooden tips (wooden toothpicks) for loading and ionization of samples. Samples could be loaded by normal pipetting onto the tip or simply dipping the tip into sample solutions. The hydrophilic and porous nature of wood allows effective adhesion of the sample solution for durable ion signals. The tip can be directly connected to nano-ESI ion sources of various mass spectrometers. Upon application of high voltage to the tip, desirable mass spectra could be obtained. We demostrated that this new technique is applicable for analysis of various samples, including organic compounds, organometallic compounds, peptides, proteins, and samples that cannot be directly analyzed by conventional ESI techniques, e.g., slurry samples and powder samples. The slim and hard properties of the wooden tip enable sampling from specific locations such as corners and small openings, indicating potential applications of the new technique in forensic investigations. The observation of electrospray ionization from wooden materials also allows us to get new insights into the materials that can be directly ionized for mass spectrometric analysis.