Cancer Diagnosis by Mass Spectroscopy

The liquid contains the substance that is to be studied, the analyte, as well as a large amount of solvent, which is usually much more volatile than the analyte. The charge contained in the capillary transfers to the liquid, which charges the analyte molecule. As like charges repel, the liquid pushes itself out of the capillary and forms an aerosol of small droplets about 10 µm across. A neutral carrier gas is sometimes used to evaporate the neutral solvent in the small droplets, which brings the charged analyte molecules closer together. The proximity of the molecules becomes unstable, however, and as the similarly charged molecules come closer together, the droplets explode. This process repeats itself until the analyte is free of solvent and is a lone ion. The lone ion then continues along to a mass analyzer.

The improved detector described in this study is a handheld wand that directs a fine water mist at a surface and then absorbs the fluid after the droplets have mixed with the material in the sample. Details were published in the November 4, 2005, issue of Angewandte Chemie.

With this method--nicknamed DESI (desorption electrospray ionization)--investigators were able to resolve chemical differences between sample areas as small as a half-millimeter. This level of resolution was sufficient to allow detection of very small tumors in a tissue sample. The technique could differentiate between diseased and non-diseased regions of tissue samples within a few seconds.

Senior author Dr. R. Graham Cooks, professor of analytic chemistry at Purdue University, said, "For now, we have shown that DESI can quickly provide medically relevant information to physicians, including the location of the boundary between cancerous and healthy tissue, accurate to within the diameter of just a few cells. That gives us cause for optimism.”




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