Biomedical Engineering Reference
In-Depth Information
thiol-derivatized single-stranded DNA, Au nanoparticles are ionized
to determine the coating thickness with electrospray-differential
mobility analysis to estimate the surface coverage of DNA.
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Alternatively, having been dried on the plate, biomolecules
docked with functionalized noble metal nanoparticles are able to
desorb into gas phase by absorbing UV laser illumination to vaporize.
These molecules are ionized via the matrix assisted laser desorption
ionization (MALDI) processes.
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One mass spectrometer is also able
to analyze biomolecules ionized via the MALDI process.
Typically prior to MALDI processes, samples are dispersed in
light-absorbing matrix such as sinapinic acid, which has very strong
UV absorption. Next when illuminated by UV laser, the matrix is
overheated to the point that it vaporizes and sometimes directly
ionizes. During matrix evaporation, analytes dispersed in the matrix
are desorbed into the gas phase in vacuum, and subsequently
undergo three types of reactions: proton transfer, electron transfer,
and cation transfer reaction. In the following reactions, m and A
represent matrix and analyte molecules, respectively.
Proton transfer reaction:
mH
+
+ A
ɦ
m + AH
+
and (m-H)
−
+ A
ɦ
m + (A-H)
−
In this reaction, protonated matrix transfers H
+
to analyte, or
deprotonated matrix extracts H
+
from analyte.
Electron transfer reaction:
m
+
+ A
ɦ
m + A
+
and m
−
+ A
ɦ
m + A
−
In the above, cationic matrix extracts an electron from analyte or
anionic matrix transfers an electron to analyte.
Cation transfer reaction:
mNa
+
+ A
ɦ
m + ANa
+
In this reaction, the cationic sodium — matrix complex transfer
sodium ion to analyte for instance.
When molecules are homogeneously dispersed in a light sorbent
matrix, the illuminated spot is instantaneously overheated upon
irradiation. The analytes, matrix molecules, and other additives such
as salts or acids at the heated point are therefore also vaporized.
Charged additives of small ions such as protons or alkaline metal
ions then attach on the moieties of high electronegativity to generate
pseudo-molecule ions.
Since noble metal nanoparticles have strong light absorbance,
docked molecules on the nanoparticle surfaces can desorb into gas
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