Matrix droplets

However, the droplet method has its own drawbacks, such as the degradation of information about the analyte s localization at a spot where the matrix droplet spreads. In general, a dispensed matrix droplet makes a spot of more than 1 mm in diameter on a tissue surface because of the lower limit of a pipetting volume of 500 nL with an ordinary micropipette. For such a large spot, it is insufficient to perform a precise high-resolution IMS. Therefore, technical improvements are needed to dispense the smallest droplets possible. 

If the block copolymer is formed in situ by chemical reaction of some dispersed-phase molecules with molecules in the matrix, droplet sizes can be much smaller than when such reactions are absent. This process, known as reactive compatibilization or grafting, is a useful strategy for obtaining fine dispersions of immiscible polymers (Sondergaard and Lyngaae-Jorgensen 1995). 

Once the section is mounted to the sample plate with the desired orientation, matrix solution is deposited on the tissue surface by electrospray deposition, aero spray, or using robotics to deposit small matrix droplets across the tissue surface before MALDI analysis [13]. The most common and least expensive devices available for applying matrix are hand-held aerosol sprayers or air brushes. The main advantage of these devices is that, with careful application, a dispersion of very small droplets... 

According to Vorm et al. (1994) and Vorm and Mann (1994), fast drying yields smaller and more evenly distributed protein-doped crystals. Hence, the protein/matrix droplets are often dried in a vacuum. Hewlett-Packard offers a a device with which you can visually track the crystallization in the vacuum. 

Recently, EWOD actuation chips were developed into a multiplexed device that was used to simultaneously cleanup four samples. A sequence of seven actuation steps were performed for each sample (1) generation of sample droplets (0.02 p.L), (2) transport and drying of sample droplets, (3) generation of rinsing droplets, (4) transport of rinsing droplets to the sample sites for selective dissolution of urea, (5) transport and disposal of the rinsing droplets, (6) generation of MALDI matrix solution droplets, and (7) delivery of matrix droplets to the dried peptide spots. 

Matrix droplets applied onto the region of interest. If only a small area of the TLC plate is of interest (for instance, to identify a defined spot), the addition of some small droplets of the matrix solution onto the (previously marked) spots of interest by a pipette or a syringe is a good approach. It is strongly recommended to use a solvent (such as water) or solveut mixture with a signilicaut surface tension because this results in a small drop size [25]. 

Once the section is mounted to the sample plate with the desired orientation, matrix solution could be also deposited on the tissue surface by electrospray deposition or using robotics to deposit small matrix droplets across the tissue surface before MALDI analysis. 

Since in SIMS imaging experiments only the top layer is sampled, the matrix layer shonld not be too thick and the analytes have to be able to migrate to the top surface layer. This combination is critical for a snccessful ME-SIMS experiment and therefore the ESD conditions have to be optimized carefully, in order to produce a fine mist of matrix droplets so the matrix arrives onto the sample surface in a wet environment. 

Sample coating for imaging MS was achieved by printing arrays of small matrix droplets using a Portrait 630 reagent multispotter (10). The volume for each droplet was... 

Da) molecules and results in analyte redistribution of less than 100 ixm. Matrix microinjection preserves tissue integrity, overcomes laser spot size imposed resolution limits, and has analyte redistribution that is limited to the size of the microinjected matrix droplet ( 10 xm). The sensor controlled aerosol and matrix microinjection protocols could conceivably be combined with matrix solution fixation. 

Fig. 25.6. Cockroach ca prepared with dried-droplet matrix deposition (a) before matrix addition, (b) after matrix addition, (c, d) MALDI LTQ Orbitrap images green color represents selected lipid ion at m/z 610.444 (c), and Pea-PK-I peptide MH+ ion at m/z 1,010.587 (d). Dark blue color shows intense DHB matrix crystals from the overlaid photograph (optical image). In contrast to the 610.444 ion, the PK-I peptide is clearly diffused out of the tissue into the matrix droplet. The MS image is indicated using the Rainbow color scheme, where relative abundance is coded as red>yellow>green>blue = zero intensity (see Notes 6 and 7).

Fig. 2. Approaches to matrix deposition. (A) Photomicrograph of a mouse hrain section, 12 p,m thick, prior to matrix deposition. The yellow rectangle represents the tissue region coated with matrix and expanded in the 4X panel. Three serial mouse brain sections were collected for matrix deposition. (B) Matrix droplet created by depositing two sequential 0.1 p,L droplets of matrix onto the same region of the tissue surface. (C) Thin film of matrix created by 10 spray cycles using a glass nebulizer. (D) Array of pL droplets deposited using a robotic ejector. Panels from a 4X and a 20X magnification are shown for each example.

Fig. 3. Protein profile generated from direct MS analysis of a matrix droplet deposited on a 12 pm human glioma section. The intensity scale has been expanded to display low intensity ion signals. The inset, displaying the m z range 4300-5300, demonstrates the complexity of the data collected from tissue samples. Over 50 ion signals can be recognized in the inset alone over 500 signals were observed across the entire spectrum.

Fig. 18.64 Schematic of particle sticking on matrix particle surface and incorporation into matrix particle during matrix droplet solidification...

On the other hand, on-target desalting within 3-AQ/CHCA droplet and selective detection of glycopeptides ions was reported (Sekiya, S. et al., 2008). Sekiya et al. found that 3-AQ/CHCA has a property to concentrate hydrophilic compounds on a small surface area of a matrix droplet (Sekiya, S. et al., 2008). Then it was confirmed by analyzing glycoprotein digests that glycopeptides were ionized from the center hydrophilic small area on 3-AQ/CHCA droplet whereas peptides were detected from the outer area on it (Fig. 10) (Sekiya, S. et al., 2008). 

Sekiya, S. Taniguchi, K. Tanaka, K (2008). Desalting within sample/ liquid matrix droplet and selective detection of sample ion species using liquid matrix. Poster (proceedings) of 2008 56th the Annual Conference on Mass Spectrometry, 2P-11, Tsukuba, Japan, May 14-16, 2008... 

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