NANOPARTICLES AS MATRICES FOR DIRECT UV-MALDI-MS ANALYSIS OF NEUTRAL CARBOHYDRATES IN PLANT TISSUES

ROSA ERRA-BALSELLS; YOUSEF GHOLIPOUR; SILVANA L. GIUDICESSI; HIROSHI NONAMI

Kyoto

Congreso; International Congress on Analytical Sciences 2011; 2011

JSAC y IUPAC

In situ characterization of biomolecules using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a valuable biochemistry tool, provided that a suitable matrix capable of laser desorption/ionization (DI) of a given metabolite is available. In the case of neutral carbohydrates, which are the main plant metabolites, poor ionization in both ionic modes is a common difficulty in MALDI-MS analysis. Except in a few reports including those from our lab, several crystalline organic matrices including 2,5-dihydroxybenzoic acid (DHB), a-ciano-4-hydroxycinnamic acid (CHCA), nor-harmane (9H-pyrido[3,4-b]indole) and 2,4,6-trihydroxyacetophenone (THAP), which are successful as the matrices in MALDI-MS of carbohydrates, fail to cause DI of carbohydrates when the matrices are deposited on the surface of plant tissues. This failure may originate from the fact that when the matrices are deposited on biological tissues and before the laser shooting, the matrices incorporate into the tissue, which yields chemical interactions and/or linkages with tissue metabolites and structural components. These interactions and/or linkages diminish or suppress the signaling of the matrix and tissue. The presence of functional groups such as carboxylic and/or phenolic groups in DHB, CHCA and THAP would cause strong tissue interactions. No such chemical interactions in the electronic ground state (before laser shooting) are theoretically expected in these potential MALDI matrices, when they are used for tissue analysis by deposition on the tissue. Nanoparticles (NPs) of diamond, titanium dioxide (TiO2), titanium silicon oxide ((SiO2)(TiO2)) and barium strontium titanium oxide ((BaTiO3)(SrTiO3)), which fulfill the mentioned condition, and Ag NPs were examined for their potential as MALDI matrices for direct laser desorption/ionization of carbohydrates, especially fructans, from plant tissue. Two sample preparation methods including solvent-assisted and solvent-free (dry) NPs deposition were performed and compared. All examined NPs except for Ag could desorb/ionize standard sucrose and fructans in positive and in negative ion mode. Ag NPs only yielded good signals for non-salt-doped samples that were measured in the negative ion mode. In the case of in vivo studies, except for Ag, all NPs studied could desorb/ionize carbohydrates from tissue in both the positive and negative ion modes. Furthermore, compared to the results obtained with soluble sugars extracted from plant tissues, fructans with higher molecular weight intact molecular ions could be detected when the plant tissues were directly profiled. The limit of detection (LOD) of fructans and the ratios between signal intensities and fructan concentrations were analyzed. NPs had similar LODs for standard fructan triose (1-kestose) in the positive ion mode and better LODs in the negative ion mode when compared with the common crystalline organic MALDI matrices used for carbohydrates (DHB and nor-harmane), or carbon nanotubes. Solvent-free NPs deposition on tissues partially improve the signal acquisition and the reproducibility averaged over all sample was more uniform.