Historical Perspective on Nanoparticles in Imaging from 1895 to 2000 - Nanotechnology for Biomedical Imaging and Diagnostics - page 8

channels between lamellar structures that could be widened by the introduction of
charged molecules into previously uncharged lecithin layers [18, 19]. These multila-
mellar liposomes were found to capture a variety of cationic species from tiny li +
ions to relatively large cholines and, as soon to be shown, imaging reporters that were
dissolved in the aqueous phase at the time of liposome formation.
following the discovery and characterization of multilamellar liposomes,
D. Papahadjopoulos and N. Miller in 1967 described the structure of small unilamellar
vesicles (SUvs) [20, 21]. This was an important development, since SUvs could be
formed with better reproducibility and could serve as a technological platform for
molecular imaging.

1.4.2 visualization of liposomes in Vivo

The majority of liposome clinical applications were historically centered in drug
delivery. However, the visualization of the liposome distribution in vivo was critical
for their clinical success and was the driving force behind the labeling of the
liposomes with imaging reporters. In the beginning of the 1970s, g. gregoriadis with
colleagues from the royal free Hospital School of Medicine in london prepared
liposomes labeled with entrapped 131 I-labeled albumin [22, 23] (fig. 1.6). Upon
in vivo administration, these liposomes were primarily deposited into the liver (major)

HO

Cholesterol

131 I

H 2 C OOCR'

O

3 H

R"COO CH

P

CHCH 2 N(CH 3 ) 3

H 2 C O O

Phosphatidylcholine

O

O

O

O

P

CH 2 CH 2 N(CH 3 ) 3

O O

O

O

H

O

1,2-Dihexadecanoyl- sn -glycero-3-
phosphocholine

figure 1.6 Design of 131 I-albumin liposomes. [ 3 H]amyloglucosidase and 131 I-labeled
albumin were entrapped into liposomes composed of phosphatidyl choline, cholesterol, and
dicetyl phosphate. 131 I-labeled albumin was also entrapped in [ 3 H]cholesterol liposomes.
(Based on refs. [22] and [23].)