unchanged, which is advantageous for quantification of ion concentrations and
biological environment [49–55].
2.7 Porphyrins, Phthalocyanines (Pcs),
and Naphthalocyanines (Ncs) and Their Nanosystems
Most porphyrins, Pcs, and Ncs are hydrophobic. To improve their solubility,
polymeric nanoparticles, liposomes, and chemical modification are employed. Liposomes have proven biocompatibility, whereas polymeric nanoparticles are readily
available for a range of chemical modifications. Porphyrins can emit fluorescence in
the NIR range that can be used for in vivo imaging. The first use of porphyrin
fluorescence for tumor detection can date back to as early as 1924 [56]. Auler and
Banzer found that hematoporphyrins can be preferentially accumulated in tumors
and lymph nodes. Following studies also found that porphyrins show great affinity
for neoplastic tissue [57]. Porphyrin fluorescence imaging could be used to assess
the success or failure of photodynamic therapy [58, 59] or imaging-guided surgical
tumor resection [60]. Another important fluorescence imaging example is that
compared with hematoporphyrins, tetratraphenylporphinesulfonate (TPPS) that
was found to better localize in tumor [61]. Porphyrin and phospholipid conjugates
were also synthesized that can form self-assembled organic nanoparticles (termed
porphysome) [62]. Porphysomes exhibit liposome-like structure with high loading
capacity, high absorption of NIR light, and excellent biocompatibility. Owing to the
presence of porphyrin, porphysomes enabled the visualization of lymph nodes by
photoacoustic imaging, and also the fluorescence could be restored upon dissociations, enabling low-background fluorescence imaging. In addition, various
porphyrin-PEG conjugates were also made for fluorescence imaging application
[63, 64]. Compared to porphyrins, Pcs and Ncs typically show higher extinction
coefficient and longer absorption wavelengths because of additional aromatic rings
fused to pyrrolic subunits. In addition, Pcs also show promise in photodynamic
therapy for cancers [65]. Zinc phthalocyanine (ZnPc) was encapsulated in liposomes
by solvent exchange method for fluorescence imaging of tumor. After introducing
into blood intravenously, ZnPc liposomes was taken up by lipoprotein and then
accumulated in the tumor; after 120 min, the fluorescence in the tumor and blood
reached a plateau [66]. Recently, silicon naphthalocyanine (SiNc) polymeric
nanoparticles have been synthesized for fluorescence imaging and photodynamic
therapy [67] (see Fig. 3e, f). SiNc was loaded in poly(ethylene glycol)-poly
(ɛ-caprolactone) (PEG-PCL) copolymers. It was demonstrated that Nc polymeric
nanoparticles have good photostability. Silicon 2,3-naphthalocyanine bis
(trihexylsilyloxide) (NIR775) was co-loaded with 2,3-bis(4-(phenyl(4-(1,2,2triphenylvinyl)phenylamino)phenyl)fumaronitrile (TPETPAFN) into DSPEPEG2000. Taking advantage of FRET between NIR775 and TPETPAFN, the
fluorescence of the nanoparticles was enhanced by 47-fold compared to excitation
40
X. Yang et al.
biological environment [49–55].
2.7 Porphyrins, Phthalocyanines (Pcs),
and Naphthalocyanines (Ncs) and Their Nanosystems
Most porphyrins, Pcs, and Ncs are hydrophobic. To improve their solubility,
polymeric nanoparticles, liposomes, and chemical modification are employed. Liposomes have proven biocompatibility, whereas polymeric nanoparticles are readily
available for a range of chemical modifications. Porphyrins can emit fluorescence in
the NIR range that can be used for in vivo imaging. The first use of porphyrin
fluorescence for tumor detection can date back to as early as 1924 [56]. Auler and
Banzer found that hematoporphyrins can be preferentially accumulated in tumors
and lymph nodes. Following studies also found that porphyrins show great affinity
for neoplastic tissue [57]. Porphyrin fluorescence imaging could be used to assess
the success or failure of photodynamic therapy [58, 59] or imaging-guided surgical
tumor resection [60]. Another important fluorescence imaging example is that
compared with hematoporphyrins, tetratraphenylporphinesulfonate (TPPS) that
was found to better localize in tumor [61]. Porphyrin and phospholipid conjugates
were also synthesized that can form self-assembled organic nanoparticles (termed
porphysome) [62]. Porphysomes exhibit liposome-like structure with high loading
capacity, high absorption of NIR light, and excellent biocompatibility. Owing to the
presence of porphyrin, porphysomes enabled the visualization of lymph nodes by
photoacoustic imaging, and also the fluorescence could be restored upon dissociations, enabling low-background fluorescence imaging. In addition, various
porphyrin-PEG conjugates were also made for fluorescence imaging application
[63, 64]. Compared to porphyrins, Pcs and Ncs typically show higher extinction
coefficient and longer absorption wavelengths because of additional aromatic rings
fused to pyrrolic subunits. In addition, Pcs also show promise in photodynamic
therapy for cancers [65]. Zinc phthalocyanine (ZnPc) was encapsulated in liposomes
by solvent exchange method for fluorescence imaging of tumor. After introducing
into blood intravenously, ZnPc liposomes was taken up by lipoprotein and then
accumulated in the tumor; after 120 min, the fluorescence in the tumor and blood
reached a plateau [66]. Recently, silicon naphthalocyanine (SiNc) polymeric
nanoparticles have been synthesized for fluorescence imaging and photodynamic
therapy [67] (see Fig. 3e, f). SiNc was loaded in poly(ethylene glycol)-poly
(ɛ-caprolactone) (PEG-PCL) copolymers. It was demonstrated that Nc polymeric
nanoparticles have good photostability. Silicon 2,3-naphthalocyanine bis
(trihexylsilyloxide) (NIR775) was co-loaded with 2,3-bis(4-(phenyl(4-(1,2,2triphenylvinyl)phenylamino)phenyl)fumaronitrile (TPETPAFN) into DSPEPEG2000. Taking advantage of FRET between NIR775 and TPETPAFN, the
fluorescence of the nanoparticles was enhanced by 47-fold compared to excitation
40
X. Yang et al.