Nanoparticles for Bioimaging: Analytical Characterization and Measurements - Nanotechnology for Biomedical Imaging and Diagnostics - page 169

a more reliable strategy is to utilize an integrating sphere that virtually eradi-
cates scattering and reveals pure absorption. an integrating sphere is a globe
covered on the inside with a highly reflective material such as magnesium oxide,
Teflon, or other fluoropolymer such as Spectralon ® (introduced in 1986 by
labsphere, Inc., United States). The latter with enough thickness offers greater than
99% diffuse reflectance over the range of 400-1500 nm [38] and is therefore well
suitable for NIR measurements. In this technique, the spectral response of the
sample placed in the integrating sphere is subtracted from the spectral response of
the integrating sphere across the whole spectrum (fig. 6.18). This method has been
used to measure absorbance spectra of silver and NIR nanoparticles [39, 40]. The

3500

ICG in milk

3000
2500
2000

ICG in
milk

ICG in
water

1500
1000
500

Integrating sphere

0
400 600 800 1000

5.00
4.00
3.00
2.00
1.00
0.00

ICG in milk

Conventional
spectrophotometer

400 600 800 1000

ICG in water

0.40

Conventional
spectrophotometer

0.30

0.20

0.10

0.00

400 600 800 1000

Wavelength (nm)

figure 6.18 Spectrum of indocyanine green (ICg) in milk using an integrating sphere
(top) or conventional spectrophotometer (middle). ICg abs. maximum is approximately
790 nm, and water peak is seen at approximately 960 nm. The spectral features of ICg are
masked by strong scattering from milk. ICg in water is shown at bottom.