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Soft cluster-induced desorption and ionization of biomolecules—Influence of surface load and morphology on desorption efficiency
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Image of FIG. 1.
FIG. 1.

(Color online) (a) Sketch of neutral cluster-induced desorption and ionization of biomolecules. Upon cluster-surface impact, a biomolecule is desorbed and ionized. Shattering of the cluster and subsequent evaporation of SO2 molecules lead to a bare or almost bare biomolecular ion in the gas phase.14 (b) Photograph of a Si substrate with three thick biofilms (n = 2.5 × 10−8 mol) which can be identified by eye and two sample spots with 10−10 mol angiotensin (in dashed circles) which cannot be observed visually. (c) SEM image taken at a cracked area of a thick angiotensin film. (d) SEM image taken on a sample covered with 10−11 mol angiotensin per 0.2 cm2. (e) AFM image of a sample covered with 10−12 mol angiotensin per 0.2 cm2.

Image of FIG. 2.
FIG. 2.

(Color online) Top: positive ion mass spectrum as obtained after cluster-surface collision on a sample prepared with 50 × 10−10 mol angiotensin II (pH = 7) on SiO2. One single predominant peak at the position of the mass of the bare biomolecule is observed. Inset: blow-up of the main panel data; a weak signal of the doubly charged biomolecule is observed. Bottom: negative ion mass spectrum from the same sample as used for the data in the top panel.

Image of FIG. 3.
FIG. 3.

(Color online) Positive ion mass spectra as obtained after cluster-surface collision on samples prepared with (a) 2.5 × 10−8 mol, (b) 5 × 10−9 mol, (c) 1 × 10−10 mol, and (d) 1 × 10−11 mol angiotensin II applied on SiO2 (pH = 2).

Image of FIG. 4.
FIG. 4.

(Color online) (a) Positive ion signal intensity of the single charged angiotensin-II-peak as a function of the amount of substance on the surface as obtained from several different data sets. The data sets including n ≥ 10−10 mol were measured with a reduced detection efficiency and are scaled accordingly. Squares represent a data set which was measured with a mixture of angiotensin and bradykinin on the surface, dots indicate the data from Fig. 3. The dashed line represents an n 2/3-dependence. (b), (c) Sketch of multilayered adsorbate aggregates on the surface and the transition to a closed film in sideview (b) and topview (c).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Soft cluster-induced desorption and ionization of biomolecules—Influence of surface load and morphology on desorption efficiency