Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry.

Nanoparticles (NPs) have been suggested as efficient matrixes for small molecule profiling and imaging by laser-desorption ionization mass spectrometry (LDI-MS), but so far there has been no systematic study comparing different NPs in the analysis of various classes of small molecules. Here, we present a large scale screening of 13 NPs for the analysis of two dozen small metabolite molecules. Many NPs showed much higher LDI efficiency than organic matrixes in positive mode and some NPs showed comparable efficiencies for selected analytes in negative mode. Our results suggest that a thermally driven desorption process is a key factor for metal oxide NPs, but chemical interactions are also very important, especially for other NPs. The screening results provide a useful guideline for the selection of NPs in the LDI-MS analysis of small molecules.

Investigation of the Chemical Interface in the Soybean-Aphid and Rice-Bacteria Interactions Using MALDI-Mass Spectrometry Imaging.

Mass spectrometry imaging (MSI) is an emerging technology for high-resolution plant biology. It has been utilized to study plant-pest interactions, but limited to the surface interfaces. Here we expand the technology to explore the chemical interactions occurring inside the plant tissues. Two sample preparation methods, imprinting and fracturing, were developed and applied, for the first time, to visualize internal metabolites of leaves in matrix-assisted laser desorption ionization (MALDI)-MSI. This is also the first time nanoparticle-based ionization was implemented to ionize diterpenoid phytochemicals that were difficult to analyze with traditional organic matrices. The interactions between rice-bacterium and soybean-aphid were investigated as two model systems to demonstrate the capability of high-resolution MSI based on MALDI. Localized molecular information on various plant- or pest-derived chemicals provided valuable insight for the molecular processes occurring during the plant-pest interactions. Specifically, salicylic acid and isoflavone based resistance was visualized in the soybean-aphid system and antibiotic diterpenoids in rice-bacterium interactions.

Multiplex MALDI-MS imaging of plant metabolites using a hybrid MS system.

Plant tissues present intriguing systems for study by mass spectrometry imaging, as they exhibit a complex metabolism and a high degree of spatial localization. This chapter presents a methodology for preparation of plant tissue sections for matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) analysis and the use of a hybrid mass spectrometer for "multiplex" imaging. The multiplex method described here provides a wide range of analytical information, including high-resolution, accurate mass imaging and tandem MS scans for structural information, all within a single experiment. While this procedure was developed for plant tissues, it can be readily adapted for analysis of other sample types.

Multiplex mass spectrometry imaging for latent fingerprints.

We have previously developed in-parallel data acquisition of orbitrap mass spectrometry (MS) and ion trap MS and/or MS/MS scans for matrix-assisted laser desorption/ionization MS imaging (MSI) to obtain rich chemical information in less data acquisition time. In the present study, we demonstrate a novel application of this multiplex MSI methodology for latent fingerprints. In a single imaging experiment, we could obtain chemical images of various endogenous and exogenous compounds, along with simultaneous MS/MS images of a few selected compounds. This work confirms the usefulness of multiplex MSI to explore chemical markers when the sample specimen is very limited.

Reaction rates and mechanism of the ascorbic acid oxidation by molecular oxygen facilitated by Cu(II)-containing amyloid-beta complexes and aggregates.

A forefront of the research on Alzheimer's disease (AD) is the interaction of amyloid beta (Abeta) peptides with redox metal ions (e.g., Cu(II), Fe(III), and Fe(II)) and the biological relevance of the Abeta-metal complexes to neuronal cell loss and homeostasis of essential metals and other cellular species. This work is concerned with the kinetic and mechanistic studies of the ascorbic acid oxidation reaction by molecular oxygen that is facilitated by Cu(II) complexes with Abeta(1-16), Abeta(1-42), and aggregates of Abeta(1-42). The reaction rate was found to linearly increase with the concentrations of Abeta-Cu(II) and dissolved oxygen and be invariant with high ascorbic acid concentrations. The rate constants were measured to be 117.2 +/- 15.4 and 15.8 +/- 2.8 M(-1) s(-1) at low (<100 muM) and high AA concentrations, respectively. Unlike free Cu(II), in the presence of AA, Abeta-Cu(II) complexes facilitate the reduction of oxygen by producing H(2)O(2) as a major product. Such a conclusion is drawn on the basis that the reaction stoichiometry between AA and O(2) is 1:1 when the Abeta concentration is kept at a much greater value than that of Cu(II). A mechanism is proposed for the AA oxidation in which the oxidation states of the copper center in the Abeta complex alternates between 2+ and 1+. The catalytic activity of Cu(II) toward O(2) reduction was found to decrease in the order of free Cu(II) > Abeta(1-16)-Cu(II) > Abeta(1-42)-Cu(II) > Cu(II) complexed by the Abeta oligomer/fibril mixture > Cu(II) in Abeta fibrils. The finding that Cu(II) in oligomeric and fibrous Abeta aggregates possesses considerable activity toward H(2)O(2) generation is particularly significant, since in senile plaques of AD patients the coexisting copper and Abeta aggregates have been suggested to inflict oxidative stress through the production of reactive oxygen species (ROS). Although Cu(II) bound to oligomeric and fibrous Abeta aggregates is less effective than free Cu(II) and the monomeric Abeta-Cu(II) complex in producing ROS, in vivo the Cu(II)-containing Abeta oligomers and fibrils might be more biologically relevant given their stronger association with cell membranes and the closer proximity of ROS to cell membranes.