Biomedical Engineering Reference
In-Depth Information
of frozen tissue was coated with four layers of SA solution. It enhanced signals of
proteins above 25 kDa with the potential to go above 100 kDa. The Gold Deposition
on top of matrix-coated rat brain tissue sections strongly enhanced imaging quality
and signal intensity for both SIMS and MALDI Imaging [ 85, 129, 130 ] .
3.4
Matrix Coating Devices (Sprayer and Spotter)
Matrix desorption is one of most important factors that governs the quality of
MALDI imaging of mass resolution, detection sensitivity, spatial resolution, and
reproducibility. Therefore, the MALDI matrix deposition should be carefully car-
ried out. It is currently achieved by two major methods: spray and spotting. For a
large quantity of samples, the matrix deposition can be automated. The commer-
cially available automated matrix application systems are based on either spray or
microspotting deposition of the matrix onto the biological tissue sections. For
example, a Portrait 630TM reagent multi-spotter (Labcyte Inc., Sunnyvale, CA) is a
fully automated device using acoustic droplet ejection system optimized to deposit
matrix onto tissue section. The droplet volume could be low to 170 picoliter (pL)
droplets. A TM-Sprayer Imaging mass spectrometry sample preparation system
(LEAP Technologies, Carrboro, NC) uses Microsoft Windows to operate interface
and graphical selection of the desired deposition area. The spray deposition can be
carried out either in linear or in serpentine modes and its track width can vary from
1 to 20 mm. An ImagePrep Station (Bruker Daltonics GmbH; Bremen, Germany) is
a piezoelectric nebulizer which creates spray. The matrix layer thickness and wet-
ness are sensor-controlled. The 20 mm droplet size is used for getting high resolu-
tion MALDI imaging. Baluya et al. [ 131 ] reported custom made automation for
matrix deposition, employing an Epson desktop inkjet printer with 5,760 × 1,440 dpi
resolution and 3 pL of minimum droplet size for MALDI matrix deposition. Chen
Y. et al. [ 132 ] described an oscillating capillary nebulizer (OCN) to spray small
droplets of matrix aerosol onto the sample surface to improve matrix homogeneity,
reduce crystal size, and control solvent effects.
For a few tissue samples, the matrix deposition can be performed manually.
A matrix solution is sprayed onto the tissue section with a hand-held thin layer
chromatography (TLC) sprayer or an artist airbrush. The reproducibility of man-
ual matrix deposition is an issue. When the manual sprayer is used, the MALDI
target plate with the tissue section is held vertically about 15-25 cm from the
sprayer nozzle. It is recommended to spray multiple coats of matrix across the
tissue section and each coating cycle consists of passing the sprayer two to five
times across the tissue section and allowing the tissue to dry for about 1-5 min.
This process is usually repeated between 10 and 20 cycles.
A TLC reagent sprayer/or a glass spray nebulizer was used for the matrix coating
onto tissue section by several researchers [ 36, 44, 76, 122, 133 ] . Puolitaival et al.
[ 134 ] reported a solvent free matrix Dry-Coating method. The matrix (DHB) was
ground for 15 min using a mortar and pestle into crystals between 1 and 40 m m in
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