Mass Spectrometric Bioanalysis Assisted by Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 281

did not involve in any extraction and derivatization steps; (b) the
smaller amounts of sample is required; (c) localization information
of metabolites can be preserved.
Moreover, AgNPs are capable of enriching target analytes from
the complex matrix. In terms of hydrophobic interaction, AgNPs
modiied with octadecanethiol can be utilized for liquid-liquid
microextraction of peptides and proteins. 46 By the combination of
liquid-liquid microextraction and atmospheric pressure — MALDI-
MS, the LOD values obtained for gramicidin in water, urine, and
plasma were 0.16, 0.13, and 0.16 μM, respectively. However, long
extraction time (1.5 h) is required when using this kind of AgNPs. To
shorten the extraction time, tetraalkylammonium bromide-capped
AgNPs were developed to enrich peptides through electrostatic
interaction, followed by atmospheric pressure — MALDI-MS. 47
Interestingly, Chang et al . showed that citrate-capped AgNPs can
be simultaneously used as extracting agents and LDI matrices in
the case of analysis of neutral estrogens. 48 Using this approach,
the concentration of estradiol and estriol in a sample of pregnant
woman's urine was determined to be 0.16 and 0.83 μM.
In comparison of AuNPs and AgNPs, PtNPs are black and are
able to effectively adsorbed laser beam all over the UV-vis region.
Thus, PtNPs are a promising matrix in LDI-MS. Yonezawa et al .
demonstrated that the determination of proteins, peptides, and
phospholipids was successfully achieved using Pt nanolowers
as LDI matrices. 49 Because Pt nanolowers have very high melting
temperature, a few Pt clusters was found in the LDI mass spectrum.
They also compared four kinds of metal NPs (i.e., Ag, Au, Cu, and Pt)
for the determination of peptides by LDI-MS. 50 In terms of detection
sensitivity, PtNPs are superior to other metal NPs.

12.3 Nanomaterials in TOF-SIMS

Another MS technique, SIMS, is a powerful method for surface
characterization. 51 SIMS used monoatomic primary ions (Ga + , Cs + ,
Au + ) to shot at a sample's surface and then eject the analyte ions from
the surface. Once the resulting secondary ions, with either positive
or negative charges, are in light, an electric ield directs them into
an MS analyzer. TOF instrument starts to dominate this ield relative
to quadrupole and magnetic-sector instruments. Compared to the