Determination of Dopamine in Cerebrospinal Fluid by MALDI-TOF Mass Spectrometry with a Functionalized Graphene Oxide Matrix

Graphite Sheet-Assisted Laser Desorption Ionization-Mass Spectrometry for Small Organic Compound Analysis

Carbon-based nanopowders have been used as ionization materials for laser desorption ionization-mass spectrometry (LDI-MS) and are very efficient at detection in low m/z regions. In this study, we aimed to develop a new sheet-type graphite material that possessed a randomly grooved nanostructured surface consisting of developed sp2-conjugated atomic carbon to facilitate the desorption/ionization of small compounds in LDI-MS. The graphite sheet exhibited higher UV absorption and provided higher ionization efficiency and survival yield in the LDI-MS detection of a thermometer ion, 4-chloro-benzopyridinium, than those of highly oriented graphite plates. These properties demonstrate that the present graphite sheet is suited for use as an LDI-MS material. Graphite sheet-assisted LDI-MS successfully detected various substances, including amino acids, peptides, and polyethylene glycol polymers, with higher ion intensities and less noise than those associated with conventional organic matrix-assisted LDI-MS (MALDI-MS). Furthermore, graphite sheet-assisted LDI-MS analysis provided more peaks (252 peaks) derived from soy sauce than those obtained by MALDI-MS (36 peaks) and required fewer preparation processes (dilution and air-dried) compared with previously established graphite carbon black-assisted LDI-MS (171 peaks) in the positive mode. This study demonstrates that graphite sheet-assisted LDI-MS has the potential for small organic compound analyses in the biomedical and food science fields.

Pneumatically Sprayed Gold Nanoparticles for Mass Spectrometry Imaging of Neurotransmitters

Using citrate-capped gold nanoparticles (AuNPs) for laser desorption ionization mass spectrometry (LDI-MS) is an approach that has demonstrated broad applicability to ionization of different classes of molecules. Here, we show a simple AuNP-based approach for the ionization of neurotransmitters. Specifically, the detection of acetylcholine, dopamine, epinephrine, glutamine, 4-aminobutyric acid, norepinephrine, octopamine, and serotonin was achieved at physiologically relevant concentrations in serum and homogenized tissue. Additionally, pneumatic spraying of AuNPs onto tissue sections facilitated mass spectrometry imaging (MSI) of rabbit brain tissue sections, zebrafish embryos, and neuroblastoma cells for several neurotransmitters simultaneously using this quick and simple sample preparation. AuNP LDI-MS achieved mapping of neurotransmitters in fine structures of zebrafish embryos and neuroblastoma cells at a lateral spatial resolution of 5 μm. The use of AuNPs to ionize small aminergic neurotransmitters in situ provides a fast, high-spatial resolution method for simultaneous detection of a class of molecules that typically evade comprehensive detection with traditional matrixes.