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Fig. 25 Noninvasive PA images of a mouse brain in vivo employing PEG-HAuNs and NIR light
at a wavelength of 800 nm. PA images received (a) before (the arrow pointed on the middle
cerebral artery), (b) 5 min after, and (c) 2 h after the intravenous injection of PEG-HAuNs.
(d, e) Differential images obtained by subtracting the preinjection image from the postinjection
images (Image d
¼
Image b
Image a; Image e
¼
Image c
Image a). (f) Open-skull photo-
graph of the mouse brain cortex obtained after the data acquisition for PAT. Scale bar
¼
2 mm.
Figure reprinted with kind permission from [
127
]
The application of PEGylated hollow gold nanospheres (HAuNs) with a diame-
ter of ~40 nm in nude mice showed the brain vasculature with great clarity and more
detail structures. The images shown in Fig.
25
depicted blood vessels as small as
~100 mm in diameter which could be clearly seen with PEG-HAuNs as PAI
system [
127
].
Beneath AuNPs, AuNRs, and HAuNs, also gold nanocages (AuNCs) have
shown great promise in PAI. In one report, 50 nm AuNCs were intradermally
injected on the left forepaw pads of Sprague-Dawley rats to image sentinel
lymph nodes (SLN) noninvasively [
157
]. With the passing of time, the contrast at
the SLN gradually and the PA signal within the SLN were increased. It was also
demonstrated that the total image depth below the skin surface of 33 mm could be
reached with good contrast which is substantial because this depth is greater than
the mean depth of SLNs in human beings [
157
]. PEGylated AuNCs were used by
Yang et al. to confirm the contrast enhancement for PA imaging in vivo [
146
]. The
particles were injected into Sprague-Dawley rats via the tail vein and better
resolved images of the cerebral cortex after administration were recorded. For the
