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

Abstract

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.

Application of flowerlike MgO for highly sensitive determination of lead via matrix‐assisted laser desorption/ionization mass spectrometry

“…They can largely absorb laser energy and transfer the energy to target molecules to facilitate their desorption and ionization . Nanomaterials can also be used to modify matrices to detect organic and inorganic compounds . Use of nanomaterials opens several exciting avenues defining new experimental constructs in academic research: (i) assisting desorption and ionization of molecules to overcome the shortcomings of conventional organic matrices; (ii) the selective enrichment of target molecules with special structures or given sizes; and (iii) on‐target immobilization and MS readout …”

Proteomic Imaging of Vestibular Schwannomas and Normal Nerves. Histopathologic Correlations

“…Besides, pure ethanol, acid matrix, and laser beam can have a detrimental effect on the analyzed tissue especially that the latter is dry and absorbs all laser energy. Another factor contributing to MALDI imprecision is the lack of spatial resolution (in general 25-50 mm) which is a known limitation of this technology and is being improved (10). A further reason is that not all sample peptides/proteins that underwent desorption will be proton-ionized and thus volatilized; therefore, a few peptides within the sample will remain undetected by the MALDI, be it mass spectrometry or imaging (10).…”