17th International Mass Spectrometry Conference :: Prague, 2006
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|Presentation date:||Thu, Aug 31, 2006|
|Presentation time:||13:30 – 15:00|
Michael Volny1, Atanu Sengupta1, Christopher B. Wilson1, E. James Davis1, Frantisek Turecek11 University of Washington, Seattle, United States
Correspondence address: Michael Volny, University of Washington, Chemistry, Bagley Hall BOX 351700, Seattle, WA, 98105 United States.
Web site: http://volny.info
Keywords: Electrospray Ionization (ESI); Nanoscale Science/Technology; Structure Determination; Surface Analysis.
Novel aspect: These results bring the first structural spectroscopic data on soft and reactively landed polyatomic ions.
Recently, there have been new exciting developments in studies of interactions between surfaces and gas-phase ions that were nondestructively deposited at landing energies of 1-200 eV. These experiments are usually referred to as soft landing, or reactive landing if the ion collision results in a bond formation. Our approach utilizes plasma pretreated metal surfaces that proved to be the advantageous for ion soft landing, as found for a wide variety of compounds ranging from proteins and polysaccharides to peptides and small molecules.1-4 We now report intense and reproducible surface-enhanced Raman spectra (SERS) of soft landed compounds that are obtained under carefully controlled conditions. These new findings are being developed into a detection and structure probe for ions landed on surfaces.
We use a special instrument for preparative ion landing and implantation that combines in-situ plasma treatment with electrospray ion source and ion transfer optics. Argon/air plasma is used to clean the surface and create a reactive metal/metal oxide layer that functions as a SERS active substrate. Once the plasma treatment is finished, the target surface is translated the ion deposition chamber where it is exposed to gas-phase ions. After ion deposition, the sample is removed from the vacuum system, and the landed ions are examined with Raman confocal microscope for SERS spectra.
The technique was initially tested for crystal violet (CV+) and rhodamine-B (RhB+). Both compounds were found to exhibit strong SERS spectra. The SERS of surface-bound CV+ and RhB+ showed frequencies that matched those in the Raman spectra measured in solution and assigned from calculations. Because SERS probes only the layer which is closest to the surface, these results indicate that the ions didnít incur damage upon reactive landing and retained their structure. From the calibration we estimate the LOD to be at a low zeptomole level, under a conservative assumption of a closest packing for the surface-bound crystal violet. Electrospraying and reactive landing of protonated cytosine, cytidine, and 2-deoxycytidine also yielded surfaces that were active in SERS spectra before and after washing with solvents. SERS spectra were also obtained for biologically relevant molecules such as IgG pentapeptide, trypsin, and a synthetic oligonucleotide. These results bring the first spectroscopic data on soft-landed polyatomic ions at zeptomole detection limits. We plan to use this new technique to probe bonding interactions between landed ions and metal surfaces and for nanostructure deposition and characterization. We are also suggesting that the technique could be utilized for fingerprinting differences in higher protein structure that are often unrecognizable by conventional MS.
1. M. Volny et al., Anal. Chem. 77, 4846 (2005).
2. M. Volny et al., Anal. Chem. 77, 4890 (2005).
3. M. Volny et al., J. Mass Spectrom. 41, 124 (2006).
4. M. Volny et al., J. Biomed. Mater. Res. accepted.