Mass Spectrometric Bioanalysis Assisted by Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 279

assisted single drop extraction and atmospheric pressure MALDI-
MS; the lowest concentrations for these peptides were 0.2 and 0.17
μM, respectively. 35 11-trimethylammonium-undecanethiol and
ω-thiol carboxylic acids functionalized AuNPs with 2 nm core
diameter were shown to have the ability for selective and eficient
extraction of the opposite charged peptides from diluted solutions. 36
When these AuNPs were utilized for the extraction of 250 μL of
sample solutions, it is demonstrated that MALDI-MS can detect
peptide concentrations as low as 500 pM.
In addition to the use of AuNPs as matrices and/or concentrating
probe, AuNPs conjugated to speciic alkanethiolate are a versatile
and eficient tool for the investigation of cellular uptake of
functionalized AuNPs. 37 Alkanethiolate molecules adsorbed on the
surface of AuNPs are ionized by LDI, producing the characteristic
mass peak. The relative quantities of four kinds of alkanethiolate-
capped AuNPs taken up by cells can be simultaneously determined
using LDI-MS. When alkanethiolate-capped AuNPs are immersed in
the aqueous salt solution such as NaI(aq), ionization of alkanethiolate
monolayers by LDI can be further enhanced. 38,39 It is suggested
that the mechanism of cation-assisted LDI seems to resemble that
observed in the earlier two-laser MS. 40

12.2.2 Silver and Platinum

Compared to the same size of AuNPs used in LDI-MS, AgNPs possess
higher extinction coeficients in the visible region. Nevertheless,
little attention has been paid to AgNP-assisted LDI-MS though
sensitive detection of peptides, 41 oleins-containing compounds, 42
and thiol-containing compounds. 43 Citrate-capped AgNPs have
been demonstrated to be used as matrices for LDI-MS analysis of
angiotensin I in the presence of 0.25% SDS. 41 Russell et al . found that
AgNPs can serve as selective ionization probe for analysis of oleins
in the presence of peptides (Fig. 12.3). 42 Also, two carotenoids,
β-carotene and phytoene, from a sample of carrot juice were
selectively ionized in AgNP-assisted LDI-MS. Wu et al . demonstrated
bare AgNPs are good LDI matrices for the analysis of aminothiols
and sulfur drugs; the LOD for each analyte was down to 7.0 nM. 43
It is found that the detection sensitivity of these analytes obtained
by AgNPs is higher than that obtained by AuNPs. LDI-MS analysis of
wax compounds on Arabidopsis stem and leaves was successfully