Mass Spectrometric Bioanalysis Assisted by Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 282

other surface techniques such as X-ray photoelectron spectroscopy
and angular electron spectroscopy, TOF-SIMS has several
advantages, including ultra-high surface sensitivity (information
depth is typically 10−15 Å), characteristic molecular fragmentation
pattern , high scan rate, and superior spatial resolution. Without
sample preparation, TOF-SIMS has been successfully used to
record chemical image with submicrometer lateral resolution at
the polymer surface. 52,53 However, low secondary ion yields still
remain challenge in this research area. To overcome this problem,
polyatomic primary ions, such as Au n

+ , have been
used to replace monoatomic ion beams because they are capable
of enhancing detection sensitivity, reducing surface damage, and
extending the detectable mass range. 54,55 For example, Schweikert
et al . irst reported that nanomaterials , aluminum monohydrate
nanowhiskers, were bombarded with a suite of projectiles (Au + ,
Au 3 + , Au 9 + , Au 400

+ , Bi n + , SF 5 + , C 60

4+ ) with kiloelectronvolt energies. 56 The yield of
secondary ions is eficient when using a massive projectile like Au 400

4+ .
Additionally, the evaporation of a monolayer of noble metal such as
Au and Ag onto sample surface , called metal-assisted SIMS, has been
found to increase the secondary ion intensities. 57,58 This metallization
procedure not only improves the quasi-molecular ion intensities,
but also enhances metal-cationized molecules. Also, the lateral
resolution of a SIMS was signiicantly improved by this metallization
procedure. 59-61 For example, Piersma et al . used metal-assisted SIMS
to directly analyze single neuroblastoma cells and rat brain tissue
sections, thereby producing high-resolution images of different
molecular distributions at cellular resolution. 60 Interestingly, the
deposition of gold onto the surface of matrix-coated rat brain also
can improve imaging quality and signal intensity in MALDI-MS.
Based on the same concept, it is found that the deposition of metal
NPs onto sample surface can enhance the yield of secondary ions
in TOF-SIMS. 62−64 Without the requirement of metal evaporation,
Winograd et al . demonstrated that the deposition of citrate-capped
AuNPs or AgNPs onto the surface of the polymers can enhance the
secondary ion emission and extend the mass range in TOF-SIMS. 62
The obtained signal intensities are comparable to those found using
metal evaporation method. Kim et al . investigated the effect of the
AuNPs and AgNPs on the secondary ion yields of triacontane upon
atomic and polyatomic projectiles in SIMS. 63 The yield of secondary
ions is strongly dependent on the speciic projectile coupled with