Comparing vacuum and extreme ultraviolet radiation for postionization of laser desorbed neutrals from bacterial biofilms and organic fullerenes

Cui

Hofstetter

et al. 2013

Analyst

Self Cite

7.87 to 10.5 eV vacuum ultraviolet (VUV) photon energies were used in laser desorption postionization mass spectrometry (LDPI-MS) to analyze biofilms comprised of binary cultures of interacting microorganisms. The effect of photon energy was examined using both tunable synchrotron and laser sources of VUV radiation. Principal components analysis (PCA) was applied to the MS data to differentiate species in Escherichia coli-Saccharomyces cerevisiae coculture biofilms. PCA of LDPI-MS also differentiated individual E. coli strains in a biofilm comprised of two interacting gene deletion strains, even though these strains differed from the wild type K-12 strain by no more than four gene deletions each out of approximately 2000 genes. PCA treatment of 7.87 eV LDPI-MS data separated the E. coli strains into three distinct groups, two “pure” groups, and a mixed region. Furthermore, the “pure” regions of the E. coli cocultures showed greater variance by PCA at 7.87 eV photon energies compared to 10.5 eV radiation. This is consistent with the expectation that the 7.87 eV photoionization selects a subset of low ionization energy analytes while 10.5 eV is more inclusive, detecting a wider range of analytes. These two VUV photon energies therefore give different spreads via PCA and their respective use in LDPI-MS constitute an additional experimental parameter to differentiate strains and species.

Section: Resultssupporting

confidence: 72%

Differentiation of microbial species and strains in coculture biofilms by multivariate analysis of laser desorption postionization mass spectra

Cui

Hofstetter

et al. 2013

Analyst

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“…Photon energy tunable VUV radiation available at synchrotron light sources has also been used for ns-LDPI analysis. 19,21,91,92,[95][96][97] Tunable VUV provides the distinct advantage of selectively ionizing different classes of compounds; a recent study of organic-mineral soil samples showed that tuning the VUV photon energy and the UV laser parameters allowed control of fragmentation of the organic analyte and enabled compounds identication with less ambiguity. 98 Overall, ns-LDPI does not display the interfering intense matrix peaks that appear in MALDI, permitting more useful information to be obtained from the low mass region (m/z < 300) of the spectra.…”

Section: Ld Combined With Postionization Of Neutralsmentioning

confidence: 99%

Ion sources for mass spectrometric identification and imaging of molecular species

Hanley

2014

Nat. Prod. Rep.

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Covering: 2013 The ability to transfer molecular species to the gas phase and ionize them is central to the study of natural products and other molecular species by mass spectrometry (MS). MS-based strategies in natural products have focused on a few established ion sources, such as electron impact and electrospray ionization. However, a variety of other ion sources are either currently in use to evaluate natural products or show significant future promise. This review discusses these various ion sources in the context of other articles in this special issue, but is also applicable to other fields of analysis, including materials science. Ion sources are grouped based on the current understanding of their predominant ion formation mechanisms. This broad overview groups ion sources into the following categories: electron ionization and single photon ionization; chemical ionization-like and plasma-based; electrospray ionization; and, laser desorption-based. Laser desorption-based methods are emphasized with specific examples given for laser desorption postionization sources and their use in the analysis of intact microbial biofilms. Brief consideration is given to the choice of ion source for various sample types and analyses, including MS imaging.

“…Ultrashort pulse laser ablation has also been used to desorb neutrals for electrospray postionization. − Vacuum ultraviolet (VUV) single photon ionization is another postionization method that has been coupled to UV ns laser desorption. − VUV single photon ionization of isolated molecules in vacuum occurs only when their ionization energies are below that of incident photons, rendering 10.5 eV VUV radiation sufficient for a wide range of analytes. − Sensitivity in VUV single photon ionization in vacuum depends on the ionization yield to produce the radical cation M •+ . The ion yield Y = σ spi IN gas , where σ spi is the photoionization cross section at a given photon energy h ν, I is the intensity of VUV radiation, and N gas is the density of gaseous neutrals .…”

Section: Introductionmentioning

confidence: 99%

Molecular Imaging and Depth Profiling of Biomaterials Interfaces by Femtosecond Laser Desorption Postionization Mass Spectrometry

Cui

ACS Appl. Mater. Interfaces

Milasinovic

et al. 2013

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Mass spectrometry (MS) imaging is increasingly being applied to probe the interfaces of biomaterials with invasive microbial biofilms, human tissue, or other biological materials. Laser desorption vacuum ultraviolet postionization with ∼75 fs, 800 nm laser pulses (fs-LDPI-MS) was used to collect MS images of a yeast-Escherichia coli co-culture biofilm. The method was also used to depth profile a three-dimensionally structured, multispecies biofilm. Finally, fs-LDPI-MS analyses of yeast biofilms grown under different conditions were compared with LDPI-MS using ultraviolet, nanosecond pulse length laser desorption as well as with fs laser desorption ionization without postionization. Preliminary implications for the use of fs-LDPI-MS for the analysis of biomaterials interfaces are discussed and contrasted with established methods in MS imaging.