Chemistry Reference
In-Depth Information
13.4.2.2 High Photostability
Traditional organic dyes and quantum dots both have obvious photo-oxidative degradation,
which leads to low photostability, and are not suitable for continuous imaging. Ln-UCNPs usually have high photostability
due to their inorganic nature and can be excited by high energy lasers.
Using 4,6-diamino-2-phenyl indole (DAPI), DiI, and Ln-UCNPs multilabelled HeLa cells as an example, Li and
co-workers have carried out the following experiment to directly prove that Ln-UCNPs have higher photostability than
common organic dyes (Figure 13.5) [2]. The signals from all these labels can be collected in an initial image. After illumi-
nation by the lasers at 405, 543, and 980 nm for 400 s, the fluorescence signals from DAPI and DiI disappeared, while the
signals from Ln-UCNPs were maintained under the excitation from the corresponding lasers.
13.4.2.3 Large Penetrating Depth
The excitation of Yb
3+
-based UCNPs is usually located at 980 nm. This NIR excita-
tion has a large penetrating depth in biological tissues. Taking Tm
3+
as the doping ion, upconversion emissions at 800 nm can
also be located in the 'optical transmission window' (650 ~ 1000 nm) of the biological tissues. Therefore, the Yb
3+
-Tm
3+
co-doped UCNPs are used to demonstrate the high penetrating ability of upconversion imaging techniques.
Zhang and co-workers employed NaYF
4
:Yb,Tm@Sio
2
nanoparticles for in-depth imaging and showed that the largest
imaging depth of cells can reach 3 mm [58]. Liu and co-workers reported a penetration depth of 0.8 cm in packing pork
(a material commonly used to act as a biotissue) for NaYF
4
:Yb,Tm nanoparticles [59]. Recently, using NaLuF
4
:Yb,Tm as a
(a)
0 S
10 S
20 S
100 S
400 S
(b)
0 S
10 S
20 S
100 S
400 S
(c)
1.0
0.8
DAPI in (a)
Dil in (a)
DAPI in (b)
Dil in (b)
UCNPs in (b)
0.6
0.4
0.2
0.0
0
100
200
Time (s)
300
400
FIgure 13.5
(a-b) Comparison of photobleaching of DAPI, DiI, and Ln-UCNPs in LSUCLm and conversional confocal microscopy
imaging. The luminescence signals of DAPI, DiI, and Ln-UCNPs are shown in blue, red, and green, respectively. Simultaneous excitation
was provided by CW lasers at 405, 543, and 980 nm with powers of approximately 19 mW, 15 μW, and 0.8 μW in (a) and 1.6, 0.13, and
19 mW in (b) in the focal plane, respectively. (c) Quantitative analysis of the signals in (a) and (b). Reprinted with permission from Ref. [2].
Copyright 2009 American Chemical Society. (
See insert for colour representation of the figure.)
)
