Peter Nemes George Washington University, Washington, D.C. 20052 Office: 202-994-6344 FAX: 202-994-5873 E-mail: petern@gwmail.gwu.edu Web: http://home.gwu.edu/~petern Job Title: Graduate Student Ph.D. in Analytical Chemistry (June, 2010) from George Washington University, Washington, D.C.

Speaker: Peter Nemes, Department of Chemistry, George Washington University, Washington, D.C. 20052

Topic: Direct Analysis and Molecular Imaging of Live Tissues and Single Cells by Infrared Laser Ablation Electrospray Ionization Mass Spectrometry

Place: Building 549, Conference Room A, NCI at Frederick, Frederick, MD

Time: Tuesday, December 2, 2008, at 2:00 PM

Abstract: Mass spectrometry in conjunction with atmospheric pressure ionization methods enables the investigation of biochemical changes in live tissues with high specificity and sensitivity. Currently available ambient ionization sources seek to facilitate in vivo studies by minimizing or eliminating chemical/physical pretreatment of samples. We have recently developed laser ablation electrospray ionization (LAESI) for the direct analysis of biological samples with sufficient water content (P. Nemes and A. Vertes, Anal. Chem., 2007, 79, 8098). With low limits of detection, a wide dynamic range for quantitation and a high mass limit of ~66.5 kDa, LAESI MS is a promising development for the study of biochemical processes in their native environment.

In this presentation, accurate mass measurements, collision activated dissociation (CAD), isotope distribution patterns are combined with information from animal/plant metabolome databases to identify primary, secondary metabolites and lipids in animal and plant tissues with analysis times of a few seconds. We demonstrate that LAESI-MS is capable of two- and three-dimensional (3D) molecular imaging of live tissues. As an example, we utilize this method to follow distributions of endogenous metabolites in a variegated plant chimera. Biosynthetic pathways functioning in the tissue are revealed with a molecular selectivity in two and three dimensions. Cross-correlation analysis of 3D distributions reveals the degree of covariance in the localization of metabolites. In light of tissue morphology, these results can add valuable information on the underlying biochemistry of tissues.

LAESI MS offers the ability to directly study individual cells. In an example, we follow the metabolites in a single egg of Xenopus Laevis. Identification of the lipid content is aided by in-situ lithiation of the lipid molecules through the electrosprayed solvent. The lithium adducts of lipids produced in this reactive LAESI yield structurally meaningful fragments in CAD experiments that improve structural elucidation. In an alternative approach, we utilize a sharpened fiber to ablate a single epidermal cell of Allium Cepa at a time for LAESI MS investigation.

Diverse fields in the life sciences, especially biochemistry, pharmacology, pathology and chemical ecology might immediately benefit from this new ionization and chemical imaging method.