Protein ion yield enhancement in matrix‐assisted laser desorption/ionization mass spectrometry after sample and matrix low‐pressure glow discharge plasma irradiation

Abstract

Rationale Plasma‐assisted ionization is widely used in mass spectrometry; in this study, a low‐pressure glow discharge is introduced as a new method to improve the detection of large proteins, and bovine serum albumin (BSA) is used as a protein model. The treatment of analyte, matrix, and the matrix/analyte mixture is evaluated under optimal conditions. Methods Low‐pressure radio‐frequency capacitively coupled plasma (RF‐CCP) treatment is utilized in the sample preparation step of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) to enhance the protein MALDI ion signal. Plasma treatment can be an effective tool for enhancing the non‐covalent binding of the analyte with the matrix, incorporation of the analyte into the matrix, production of matrix/analyte crystals, and analyte protonation through plasma activation, resulting in an improved MALDI ion signal. Results Fourier‐transform infrared (FTIR) spectroscopy allows us to distinguish between the functional groups of plasma‐treated and control samples. In addition, optical emission spectroscopy (OES) determines the plasma species, and zeta potential analysis characterizes the potential difference between plasma‐treated and control samples before MALDI‐TOF MS analysis. Plasma‐treated BSA can provide a five‐times enhancement of ion intensity. The combination of the plasma‐treated analyte with the plasma‐treated matrix leads to an increase in the ion intensity by a factor of 14. Conclusions Low‐pressure glow discharge plasma treatment greatly enhances MALDI ion signals, with a noticeable increase in incorporation, co‐crystallization, protonation, and the concentration of the sample functional groups.

Increasing DESI-MS Ion Signal by Plasma Treatment

“…Plasma is produced by the gas discharge mechanism at low pressure or atmospheric pressure. The generation of reactive oxygen and nitrogen species (RONS) by plasma is the main reason for the effect of plasma on different samples. , …”

“…Plasma as an ion source coupled with MS includes direct analysis in real time (DART), plasma-assisted desorption ionization (PADI), dielectric barrier discharge ionization (DBDI), low-temperature plasma (LTP), flowing atmospheric-pressure afterglow (FAPA), and plasma spray ionization (PSI) . On the other hand, plasma can used as a surface treatment tool before mass spectrometry to enhance the ion signal. , …”

“…On the basis of our previous study, low-pressure glow discharge plasma treatment in the sample preparation step of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) enhances the bovine serum albumin (BSA) protein ion signal by increasing in protonation, incorporation, co-crystallization, and the concentration of the sample functional groups. In addition, we demonstrated that nonequilibrium atmospheric-pressure plasma jets can improve the protein MALDI ion signal due to plasma activation and more protonation …”

“…The glow discharge plasma (GDP) selected for this work is portable, accessible, and low cost. Plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) techniques such as DART and LTP are suitable for small compounds (lower than 1000 Da), but plasma treatment prior to MS analysis can improve the signal for both small and large analytes. , In this study, GDP adds a new step to DESI sample preparation to increase detection accuracy.…”

4‐Mercaptobenzoic acid‐assisted laser desorption/ionization mass spectrometry for sensitive quantification of cesium and strontium in drinking water

“…Although the conventional techniques have been widely applied in metal analysis, these methods were still challenged by complex sample preparation, were time‐consuming, and required large sample and solvent volumes, etc. In contrast, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS), as a rapid and high‐throughput mass spectrometry technique with the advantages of extremely low sample consumption (as low as 1 μL), high sensitivity and simple instrumental operation, is an excellent analytical technique which is widely used in biology and chemistry 16 . However, due to the poor desorption/ionization efficiency and severe background interference of matrices, it is unsuitable for the analysis of low‐molecular‐weight compounds (<500 Da, e.g.…”