Gold Nanoparticles in Biomedicine - Bionanotechnology: Global Prospects - page 64

FIGURE 3.5
Drug.delivery.using.AuNPs.embedded.in.a.hydrogel..AuNPs.are.embedded.in.a.hydrogel.encapsulating.the.
drug..NIR.irradiation.leads.to.hydrogel.collapse.and.drug.release.
Hong.et.al. 89 .coated.2.nm.AuNPs.with.a.monolayer.of.a.cationic.tetra(ethylene.glycol)-
conjugated.ligand.and.a.thiolated.hydrophobic.dye..The.AuNPs.were.then.incubated.with.
human.liver.cells.(Hep.G2)..The.cationic.ligand.allowed.the.AuNPs.to.cross.the.cell.mem-
brane,.and.the.dye.functioned.as.both.a.model.for.hydrophobic.drugs.and.a.luorophore.
probe,.allowing.the.detection.of.its.release.by.luorescent.spectroscopy..Strong.intracellu-
lar.luorescence.was.detected.after.96.h.of.incubation.
Light,. on. the. other. hand,. can. be. used. as. an. external. stimulus. to. trigger. drug. release..
Gold.nanoshells.have.been.embedded.in.a.temperature-sensitive.polymer-hydrogel.and.
irradiated.at.808.nm.laser.wavelength. 90 .The.nanoshells.convert.the.absorbed.radiation.into.
heat,.which.shrinks.the.hydrogel.reversibly,.and.the.drug.is.released.(Figure 3.5)..The.same.
hydrogel.principle.has.been.applied.using.nanorods.coated.with.poly(nisopropylacryamide).
(PNIPAM). gel. 91,92 . Another. way. has. also. been. done. by. Wijaya. et. al., 93 . where. controlled.
drug.release.was.achieved.by.using.two.sets.of.nanorods.of.different.lengths.conjugated.
to. two. different. oligonucleotides.. Irradiation. at. 800. nm. wavelength. melted. the. shorter.
set.of.nanorods.into.nanospheres,.causing.the.release.of.the.conjugated.oligonucleotides.
(Figure 3.6)..Melting.and.release.were.achieved.in.the.set.of.longer.nanorods.under.irradia-
tion.at.1,100.nm..Ipe.et.al. 94 .delivered.amino.acids.using.AuNPs.attached.to.spiropyran..In.
its.open.form,.which.is.induced.by.UV.radiation,.spiropyran.forms.complexes.with.amino.
acids..These.complexes.can.then.be.broken.by.returning.the.molecule.to.its.closed.form.by.
irradiation.with.visible.light.or.heat.
3.5.1.1.4 Photodynamic Therapy (PDT)
Photodynamic. therapy. (PDT). is. another. technique. used. in. cancer. therapy,. where. cyto-
toxic.singlet.oxygen.is.locally.generated.by.light.activation.of.a.nontoxic.photosensitizer..
The. photosensitizer. absorbs. light. at. suitable. wavelengths,. the. absorbed. energy. is. used.
to.excite.oxygen.into.a.singlet.state,.and.the.singlet.oxygen.causes.the.degradation.of.cel-
lular. components.. Photosensitizers. are. more. likely. to. be. taken. up. by. cancer. cells. than.
normal.ones. 95 .Targeting.the.location.of.the.tumor.using.light.within.600-700.nm.in.the.