Bioconjugation of Noble Metal Nanoparticles and Their Applications to Biolabeling and Bioimaging - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 19

chelate, nitrilotriacetic acid (NTA)-nickel (II) with highly selectively
conjugated with polyhistidine (His) tags, because His tags can be
readily engineered on most proteins for a speciic interaction to
nickel. NTA-Ni-Au nanoparticles have shown high speciic targeting
eficiency to histidine-tagged proteins or peptides for speciic tumor-
targeting. 45,46

2.3 Applications of Noble Metal Nanoparticles

to Biolabeling and Bioimaging

2.3.1 X-Ray Computed Tomography

X-ray computed tomography (CT) is one of common tools used
in medical diagnosis. Iodine-based molecules are frequently
used contrast agents for CT because of the high X-ray absorption
coeficient of iodine. Iodinated compounds, however, make only very
short imaging times and can cause toxicity in kidneys. The use of
gold nanoparticle as a contrast agent is an attractive alternative. Due
to its higher X-ray absorption coeficient than iodine (1.94 cm 2 /g
at 100 keV), the feasibility of using gold nanomaterials (5.16 cm 2 /g
at 100 keV) as a potential CT contrast agent in vivo is currently
under studies. For example, PEG-coated gold nanoparticles 6 and
gold nanoparticles within gum arabic matrix 47 are able to generate
high eficient in vivo CT angiogram images of the heart and vessels.
The PEG-hybrid gold nanoparticles had not only clearly enhanced
the CT signal for the aorta, but also obtained long circulation times
in vivo with better biocompatibility than the iodinated imaging
agent (Ultravist ® ). 6 The additional experiments based on the
intravenous injection of PEG-hybrid gold nanoparticles into
hepatoma-bearing rats also exhibited a clear CT contrast in hepatoma
tissue. It is noted that the gold nanoparticles provided additional
potential functionality in the therapeutic applications once the gold
nanoparticle exposed to high energy irradiation. 47,48

2.3.2 Magnetic Resonance Imaging

The development of new contrast agents based on Au nanoparticles
for MR imaging is progressing now. Signiicant effort has
demonstrated the combinations of MR imaging materials with
promising biolabling agents. For example, Au/DOTA-Gd 3+ hybrids