DIOS-MS

Laser Desorption Assays - MALDI-MS, DIOS-MS, and SAMDI-MS... 

Due to the hydrophobicity of the silicon surface, samples are typically dissolved in water or mixtures of water and methanol. While samples dissolved in pure non-polar solvents tend to spread over the whole surface, aqueous/organic mixtures form droplets that stay localized to a small surface area. Additionally, mixtures also guarantee that the sample penetrates sufficiently deep into the silicon. Spotted volumes are typically in the low microliter to submicroliter range. Traditionally, sample spotting in DIOS-MS is carried out using pipettes, which mostly suffers from an inhomogeneous analyte distribution. This can be overcome by... 

Although DIOS-MS is mainly a tool for qualitative analysis, many examples have shown that quantitative analysis is possible when internal standards are used. These may either be isotope-labelled - mostly deuterated - compounds or structurally related analogues. For example, subsequent to electrospray deposition, amino acids such as phenylalanine and tyrosine have been successfully quantified by means of DIOS-MS using their deuterated analogues as internal standards. 

In contrast to established MALDI-MS techniques, DIOS-MS is a comparatively new technique. However, over the last five years, it has been gaining steadily more attention and promising results have already been obtained in all those cases, where interference from classic MALDI matrices needed to be avoided. Owing to the fact that DIOS-MS is still a juvenile technique, it is hard to predict future developments, but especially in the field of silicon modifications further promising developments can be foreseen, accompanied by new applications. 

A comparison of sensitivity of some dmgs using DIOS-MS and MALDI-MS was performed. Table 11.1 contains the data, which show that on the Waters MALDI-LR-TOF mass spectrometer DIOS may be a preferable technique. These four drugs were 2-28 times more sensitive using DIOS than MALDI. Recent... 

It was clear from this early work that mass spectrometric analysis would be the most appropriate technique to detect hit compounds for in situ Click chemistry applications. Although the DIOS-MS method was able to directly detect the low quantity of triazole product conversion in the presence of large amounts of protein and parent fragments, the sensitivity for this measurement was very low, with a poor signal-to-noise ratio. It was therefore both logical and desirable to optimize the sensitivity and selectivity of the MS... 

Lee JC, Wit CY, Apon JV, Siuzdak G, Wong CH. Reactivity-based one-pot synthesis of the tumor-associated antigen N3 minor octasaccharide for the development of a photocleavable DIOS-MS sugar array. Angew. Chem. Int. Ed. 2006 45 2753. 

Desorption/lonization on Silicon Mass Spectrometry (DIOS-MS)... 

Fig. 16.18. DIOS-MS using porous silicon, (a) Four porous silicon substrates mounted upon a MALDI spectrometer plate, (b) Desorption/ ionization of deposited analytes, (c) Cross-...

Fig. 16.19. Mass spectrometry of WIN antiviral drug, (a) DIOS-MS spectrum ofWIN deposited upon porous silicon. Inset DIOS-PSD-MS spectrum of WIN. (b) MALDI-MS spectrum of WIN dispersed in a-cyano-4-hydroxycinnamic acid (HCCA). (c) Attempted...

The advances of DIOS-MS since its earliest work promise the reliable measurement of low-molecular weight species in tandem with, and possibly without, MALDI-MS. Additionally, the well-established integration of devices upon silicon chips offer the ability to fashion samples capable of supporting multiple analyses in series or parallel, confining all characterizations of biological or chemical species to a lone substrate. It is clear that surface termination and bound functionalities are important not only for analysis but also for recycling the porous silicon chip for multiple uses. 

Fig. 16.22. DIOS-MS spectra of diethylamine measured from porous silicon (top), F -etched roughened silicon (bottom), and 0 -etched roughened HOPG (middle).

Fig. 16.23. DIOS-MS spectra of bradykinin from UV and IR laser sources. Insets Expanded m/z = 1061 peak of bradykinin.

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