Abstract
In recent years, matrix-assisted laser desorption/ionization (MALDI) has become the main tool for the study of biological macromolecules, such as protein nano-machines, especially in the determination of their molecular masses, structure, and post-translational modifications. A key role in the classical process of desorption and ionization of the sample is played by a matrix, usually a low-molecular weight weak organic acid. Unfortunately, the interpretation of mass spectra in the mass range of below m/z 500 is difficult, and hence the analysis of low molecular weight compounds in a matrix-assisted system is an analytical challenge. Replacing the classical matrix with nanomaterials, e.g., silver nanoparticles, allows improvement of the selectivity and sensitivity of spectrometric measurement of biologically important small molecules. Nowadays, the nanostructure-assisted laser desorption/ionization (NALDI) approach complements the classic MALDI in the field of modern bioanalytics. In particular, the aim of this work is to review the recent advances in MALDI and NALDI approaches.
Highlights
The problematic nature of modern bioanalytical research is mainly related to the complex biological matrix and the extremely low concentration of tested analytes in the sample, the amount of which is usually small and often representative for several cells
Another approach is described in the work of Yang et al [33], who have applied the two-dimensional gels coupled with matrix-assisted laser desorption/ionization (MALDI)-TOF Mass spectrometry (MS) for detection of cow milk adulteration in different types of milk mixtures
To the previous paper, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was applied to confirm the formation of the covalent glycoslated chlorogenic acid (CA)–LTF conjugates; data from this study provided the mass of native LTF, shown as a m/z 84011.15
Summary
The problematic nature of modern bioanalytical research is mainly related to the complex biological matrix and the extremely low concentration of tested analytes in the sample, the amount of which is usually small and often representative for several cells (e.g., cellular lysates). In MALDI, the phenomenon of fragmentation (of both proteins and polypeptides) is practically non-existent, and, as a result, no signals from fragmentation ions (resulting from the disintegration of particles in the ionizer) are observed in the spectra In this situation, signals from the matrix or its adducts with the components of the analyzed sample (e.g. adduct [MH]+) are presented. Complete elimination of both sodium and potassium ions from the system (e.g., used solution) is practically impossible (for example due to the use of laboratory glassware), on MALDI spectra CHCA matrix-cluster peaks are present These complexes (clusters) are formed by interaction of the cations of the discussed metals with the carboxyl group or π electrons of the aromatic ring of the CHCA molecule (so-called sandwich structures), and depending on the number of molecules involved in the cluster, they can take various masses. Matrix clusters are formed only and exclusively in the presence of organic compounds—during the co-crystallization of CHCA with the analyte, causing suppression and difficulties in the analysis of low-molecular compounds [22]
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