Laser spot size and laser power dependence of ion formation in high resolution MALDI imaging

Guenther, Sabine; Koestler, Martin; Schulz, O.; Spengler, Bernhard

doi:10.1016/j.ijms.2010.03.014

Cited by 84 publications

(86 citation statements)

References 27 publications

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“…The I versus F curves shown within Figure 4 all have the similar general trends to those observed from peptides within the literature [2,7,9] whereby the low fluence data do not feature any detected ions, then as the fluence is increased past threshold, a steep rise in detected ion intensity is observed. For the single ion data, the curves then plateau soon after this initial increase and may even decrease again as fluence increases, whereas the TIC curves typically continue to increase to the maximum fluence, though the rate of increase is seen to drop off at the higher fluences, particularly for the 50 μm round fiber data (SI Figure S5).…”

Section: Optic Fiber Core Shape and Laser Beam Profilingsupporting

confidence: 77%

“…An increase in laser energy in laser desorption/ablation-type studies can lead to an increase in fragmentation of ejected molecules [2,7,9]. Within this study, an increase in fragmentation (monitored by proxy with the lipid headgroup fragment peak at m/z 184.1 and PC lipid sidechain loss fragment at m/z 577.5, data not shown) was observed with increasing fluence in absolute terms as well as relative to the intensity of the fragment's parent molecule and to the TIC.…”

Section: Discussionmentioning

confidence: 99%

“…The effect of fluence on the detected ion intensity has been investigated by a number of groups for peptide and protein standards, e.g., substance P, with a range of matrices, e.g., 2,5-dihydroxybenzoic acid (2,5-DHB) or α-cyano-hydroxycin namic acid (CHCA) [2,3,7,9]. There have not, however, been any similar investigations employing other analyte classes, such as lipids or drugs.…”

Section: Introductionmentioning

confidence: 99%

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Probing the Relationship Between Detected Ion Intensity, Laser Fluence, and Beam Profile in Thin Film and Tissue in MALDI MSI

Steven

Race

Bunch

2016

J. Am. Soc. Mass Spectrom.

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Abstract. Matrix assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) is increasingly widely used to provide information regarding molecular location within tissue samples. The nature of the photon distribution within the irradiated region, the laser beam profile, and fluence, will significantly affect the form and abundance of the detected ions. Previous studies into these phenomena have focused on circular-core optic fibers or Gaussian beam profiles irradiating dried droplet preparations, where peptides were employed as the analyte of interest. Within this work, we use both round and novel square core optic fibers of 100 and 50 μm diameter to deliver the laser photons to the sample. The laser beam profiles were recorded and analyzed to quantify aspects of the photon distributions and their relation to the spectral data obtained with each optic fiber. Beam profiles with a relatively small number of large beam profile features were found to give rise to the lowest threshold fluence. The detected ion intensity versus fluence relationship was investigated, for the first time, in both thin films of α-cyano-4-hydroxycinnamic acid (CHCA) with phosphatidylcholine (PC) 34:1 lipid standard and in CHCA coated murine tissue sections for both the square and round optic fibers in continuous raster imaging mode. The fluence threshold of ion detection was found to occur at between~14 and~64 J/m 2 higher in tissue compared with thin film for the same lipid, depending upon the optic fiber employed. The image quality is also observed to depend upon the fluence employed during image acquisition.

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Section: Optic Fiber Core Shape and Laser Beam Profilingsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Probing the Relationship Between Detected Ion Intensity, Laser Fluence, and Beam Profile in Thin Film and Tissue in MALDI MSI

Steven

Race

Bunch

2016

J. Am. Soc. Mass Spectrom.

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“…This confirms the signal decrease is more important than expected by simple reduction of the laser spot size, by 1 to 3 orders of magnitude, depending on the laser profile. 23 Spatial Resolution. Figure 3 shows examples of matrix layer removal after irradiation of the sample at high laser fluence through masks of different apertures on the Voyager DE-STR Elite.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

On the Origin of Increased Sensitivity and Mass Resolution Using Silicon Masks in MALDI

Diologent

Franck²,

Wisztorski³

et al. 2014

Anal. Chem.

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Since its development, MALDI has proved its performance in the analysis of intact biomolecules up to high molecular weights, regardless of their polarity. Sensitivity of MALDI instruments is a key point for breaking the limits of observing biomolecules of lower abundances. Instrumentation is one way to improve sensitivity by increasing ion transmission and using more sensitive detection systems. On the other side, improving MALDI ion production yields would have important outcomes. MALDI ion production is still not well-controlled and, indeed, the amount of ions produced per laser shot with respect to the total volume of desorbed material is very low. This has particular implications for certain applications, such as MALDI MS imaging where laser beam focusing as fine as possible (5− 10 μm) is searched in order to reach higher spatial resolution images. However, various studies point out an intrinsic decrease in signal intensity for strong focusing. We have therefore been interested in developing silicon mask systems to decrease an irradiated area by cutting rather than focusing the laser beam and to study the parameters affecting sensitivity using such systems. For this, we systematically examined variation with laser fluence of intensity and spectral resolution in MALDI of standard peptides when using silicon-etched masks of various aperture sizes. These studies demonstrate a simultaneous increase in spectral resolution and signal intensity. Origin of this effect is discussed in the frame of the two-step ionization model. Experimental data in the low fluence range are fitted with an increase of the primary ionization through matrix-silicon edge contact provided by the masks. On the other hand, behavior at higher fluence could be explained by an effect on the secondary ionization via changes in the plume dynamics.

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“…Numerous fundamental studies were conducted to investigate the influence of relevant Binput parameters^on the MALDI ion yields, like the type and physicochemical properties of the MALDI matrix [21], the analyte-to-matrix ratio in the sample [22], or those of the laser irradiation parameters like wavelength [23][24][25], fluence [23,24,[26][27][28][29], and pulse width [30,31].…”

Section: Introductionmentioning

confidence: 99%

Influence of the Laser Spot Size, Focal Beam Profile, and Tissue Type on the Lipid Signals Obtained by MALDI-MS Imaging in Oversampling Mode

Wiegelmann

Dreisewerd

Soltwisch

2016

J. Am. Soc. Mass Spectrom.

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Abstract. To improve the lateral resolution in matrix-assisted laser desorption/ ionization mass spectrometry imaging (MALDI-MSI) beyond the dimensions of the focal laser spot oversampling techniques are employed. However, few data are available on the effect of the laser spot size and its focal beam profile on the ion signals recorded in oversampling mode. To investigate these dependencies, we produced 2 times six spots with dimensions between~30 and 200 μm. By optional use of a fundamental beam shaper, square flat-top and Gaussian beam profiles were compared. MALDI-MSI data were collected using a fixed pixel size of 20 μm and both pixel-by-pixel and continuous raster oversampling modes on a QSTAR mass spectrometer. Coronal mouse brain sections coated with 2,5-dihydroxybenzoic acid matrix were used as primary test systems. Sizably higher phospholipid ion signals were produced with laser spots exceeding a dimension of~100 μm, although the same amount of material was essentially ablated from the 20 μm-wide oversampling pixel at all spot size settings. Only on white matter areas of the brain these effects were less apparent to absent. Scanning electron microscopy images showed that these findings can presumably be attributed to different matrix morphologies depending on tissue type. We propose that a transition in the material ejection mechanisms from a molecular desorption at large to ablation at smaller spot sizes and a concomitant reduction in ion yields may be responsible for the observed spot size effects. The combined results indicate a complex interplay between tissue type, matrix crystallization, and laser-derived desorption/ablation and finally analyte ionization.

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Laser spot size and laser power dependence of ion formation in high resolution MALDI imaging

Cited by 84 publications

References 27 publications

Probing the Relationship Between Detected Ion Intensity, Laser Fluence, and Beam Profile in Thin Film and Tissue in MALDI MSI

Probing the Relationship Between Detected Ion Intensity, Laser Fluence, and Beam Profile in Thin Film and Tissue in MALDI MSI

On the Origin of Increased Sensitivity and Mass Resolution Using Silicon Masks in MALDI

Influence of the Laser Spot Size, Focal Beam Profile, and Tissue Type on the Lipid Signals Obtained by MALDI-MS Imaging in Oversampling Mode

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