title: Nanotip Ambient Ionization Mass Spectrometry.
abstract: A method called nanotip ambient ionization mass spectrometry (NAIMS) is described, which applies high voltage between a tungsten nanotip and a metal plate to generate a plasma in which ionized analytes on the surface of the metal plate are directed to the inlet and analyzed by a mass spectrometer. The dependence of signal intensity is investigated as a function of the tip-to-plate distance, the tip size, the voltage applied at the tip, and the current. These parameters are separately optimized to achieve sensitivity or high spatial resolution. A partially observable Markov decision process is used to achieve a stabilized plasma as well as high ionization efficiency. As a proof of concept, the NAIMS technique has been applied to phenanthrene and caffeine samples for which the limits of detection were determined to be 0.14 fmol for phenanthrene and 4 amol for caffeine and to a printed caffeine pattern for which a spatial resolution of 8 ± 2 μm, and the best resolution of 5 μm, was demonstrated. The limitations of NAIMS are also discussed.
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.
authors.forename: Zhenpeng
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.
authors.forename: Jae Kyoo
authors.initials: JK
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5080, United States.
authors.forename: Richard N
authors.initials: RN
authors.lastname: Zare