Reactive and soft landing of polyatomic gas-phase ions on plasma-treated metal surfaces
Non-destructive physical isolation of ions from the gas phase with preservation of their structure is referred to as ion soft landing. The presented dissertation describes in-situ plasma oxidized dry metal surfaces as novel and advantageous collection targets (plates) for soft landing experiments. A new term, reactive landing, is introduced to cover ion-surface collisions that result in surface immobilization of the impacting ion but without significant damage.Soft and reactive landing on a plasma-treated metal surface of multiply protonated protein ions results in a substantial retention of protein function, as demonstrated for trypsin and streptavidin. The majority of trypsin ions soft-landed at hyperthermal kinetic energies retain enzymatic activity. The landed streptavidin can be washed into solution where they show affinity to biotin. The layer of streptavidin monomer that is immobilized on the surface can be detected if fluorescence-tagged and retains the ability to reversibly bind biotin. A mechanism is proposed to explain nondestructive protein ion discharge on the surface that considers proton migration from the soft-landed cations to the metal oxide layer and metal ion reduction by electron transfer from the bulk metal.Soft landing of singly charged gas-phase ions on dry metal surfaces that were pretreated by plasma results in 0.1-6% total yields of recovered intact compounds. The plasma-treated metal surfaces are shown to be useful for preparative separation of organic and biological molecules by mass spectrometry. The instrumental improvement and conditions for reactive immobilization of small molecules are discussed.The surface-enhanced Raman spectroscopy (SERS) was used to gain structure-specific bonding information for polyatomic cations and molecules soft-landed on plasma-treated silver substrates. While enhancing Raman scattering 105-10 6 fold, the metal surface effectively quenches the fluorescence that does not interfere with the Raman spectra. The spectra from zeptomole amounts of soft-landed compounds were found sufficiently intense and reproducible to allow identification of Raman active vibrational modes for structure assignment.Research results that open new paths to potential applications of soft and reactive landing are described in the last chapter. They include modification of surfaces for biomedical purposes as well as development of protein arrays and modification of CMOS chips.
- Chemistry