Effects of Carbon Nanowalls (CNWs) Substrates on Soft Ionization of Low-Molecular-Weight Organic Compoundsin Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS).

Ryusei Sakai,Mineo Hiramatsu,Naohiro Shimizu,Tomonori Ichikawa,Takayuki Ohta,Kenji Ishikawa,Hiroki Kondo,Masaru Hori

doi:10.3390/nano11020262

Abstract

Carbon nanowalls (CNWs), which are vertically oriented multi-layer graphene sheets, were employed in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) measurements to detect low-molecular-weight organic compounds. CNWs substrates with widely different wall-to-wall distances from 142 to 467 nm were synthesized using a radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) system with nanosecond pulse biasing to a sample stage. When survival yield (SY) values of N-benzylpyridinium chloride (N-BP-Cl) were examined, which is commonly used to evaluate desorption/ionization efficiency, a narrower wall-to-wall distance presented a higher SY value. The highest SY value of 0.97 was realized at 4 mJ/cm2 for the highest-density CNWs with a wall-to-wall distance of 142 nm. The laser desorption/ionization effect of arginine, an amino acid, was also investigated. When CNWs with a narrower wall-to-wall distance were used, the signal-to-noise (SN) ratios of the arginine signals were increased, while the intensity ratios of fragment ions to arginine signals were suppressed. Therefore, the CNWs nanostructures are a powerful tool when used as a SALDI substrate for the highly efficient desorption/ionization of low-molecular-weight biomolecules.

Highlights

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful method for the rapid, noninvasive, and sensitive sampling of biological fluids due to the soft-ionization properties of biomolecules such as proteins, amino acids, DNA, RNA, as well as synthetic and biopolymers [1,2]
It has been reported that an array of SiNWs with diameters of 10–40 nm, lengths less than 5 μm, and density less than 10 wires/μm2 are highly effective for the promotion of soft ionization at lower laser fluence compared with previous cases of porous Si and conventional MALDI [9]
The distance between the capacitively coupled plasma (CCP) upper electrode and the lower sample stage was 30 mm. These two plasma sources were connected through a mesh electrode as an upper electrode for the CCP, and 100 sccm CH4 and 50 sccm H2 gases were introduced into the CCP and surface-wave plasma (SWP) chambers, respectively

Summary

Introduction

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful method for the rapid, noninvasive, and sensitive sampling of biological fluids due to the soft-ionization properties of biomolecules such as proteins, amino acids, DNA, RNA, as well as synthetic and biopolymers [1,2]. It is well known that MALDI mass spectra are generally convolved with peaks of matrix-related fragments, especially in the case of low-molecular-weight analytes with mass-to-charge ratios (m/z) of less than 700 [2]. To solve this problem, Sunner et al first reported surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) as a matrix-free desorption/ionization method in 1995 [3]. It has been reported that an array of SiNWs with diameters of 10–40 nm, lengths less than 5 μm, and density less than 10 wires/μm are highly effective for the promotion of soft ionization at lower laser fluence compared with previous cases of porous Si and conventional MALDI [9]

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Results

Conclusion