Immunohistochemistry (IHC) combined with fluorescence microscopy provides an important and widely used tool for researchers and pathologists to image multiple biomarkers in tissue specimens. However, multiplex IHC using standard fluorescence microscopy is generally limited to 3–5 different biomarkers, with hyperspectral or multispectral methods limited to 8. We report the development of a new technology based on novel photocleavable mass-tags (PC-MTs) for facile antibody labeling, which enables highly multiplexed IHC based on MALDI mass spectrometric imaging (MALDI-IHC). This approach significantly exceeds the multiplexity of both fluorescence- and previous cleavable mass-tag-based methods. Up to 12-plex MALDI-IHC was demonstrated on mouse brain, human tonsil, and breast cancer tissues specimens, reflecting the known molecular composition, anatomy, and pathology of the targeted biomarkers. Novel dual-labeled fluorescent PC-MT antibodies and label-free small-molecule mass spectrometric imaging greatly extend the capability of this new approach. MALDI-IHC shows promise for use in the fields of tissue pathology, tissue diagnostics, therapeutics, and precision medicine.

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.

A forefront of the research on Alzheimer's disease (AD) is the interaction of amyloid beta (Aβ) peptides with redox metal ions (e.g., Cu(II), Fe(III) and Fe(II)) and the biological relevance of the Aβ-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 Aβ(1-16), Aβ(1-42), and aggregates of Aβ(1-42). The reaction rate was found to linearly increase with the concentrations of Aβ-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 µM) and high AA concentrations, respectively. Unlike free Cu(II), in the presence of AA, Aβ-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 Aβ 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 Aβ complex alternates between 2+ and 1+. The catalytic activity of Cu(II) towards O 2 reduction was found to decrease in the order of free Cu(II) > Aβ(1-16)-Cu(II) > Aβ(1-42)-Cu(II) > Cu(II) complexed by the Aβ oligomer/fibril mixture > Cu(II) in Aβ fibrils. The finding that Cu(II) in oligomeric and fibrous Aβ aggregates possesses considerable activity towards H 2 O 2 generation is particularly significant, since in senile plaques of AD patients the co-existing copper and Aβ aggregates have been suggested to inflict oxidative stress through the production of reactive oxygen species (ROS). Although Cu(II) bound to oligomeric and fibrous Aβ aggregates is less effective than free Cu(II) and the monomeric Aβ-Cu(II) complex in producing ROS, in vivo the Cu(II)-containing Aβ oligomers and fibrils might be more biologically relevant given their stronger association with cell membranes and the closer proximity of ROS to cell membranes.

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.