Biomedical Engineering Reference
In-Depth Information
active oxyoxalate and an oxidant, typically hydrogen peroxide, in
the presence of a fluorophore.
26
This reaction proceeds via a
two-step process: first hydrogen peroxide reacts with the oxalate
ester, generating the high-energy dioxetandione intermediate.
This then excites the fluorescent dye, which upon relexation
chemiluminesces and emits a photon.
27
Peroxalate chemilumines-
cence has been widely employed for the detection of hydrogen
peroxide and fluorescent molecules due to its intrinsic nanomo-
lar sensitivity and specificity to hydrogen peroxide.
28
Despite these
appealing features,
in vivo
imaging of hydrogen peroxide based on
peroxalate chemiluminescence was very challenging because of the
instabilityoftheperoxalateinwateranditswaterinsolubility.More-
over, the peroxalate chemiluminescence reaction requires biocom-
patible nanosized scaffolds that allow a three-component reaction
in a biologicalenvironment.
11
-
13
Recently, peroxalate chemiluminescence-based
in vivo
hydro-
gen peroxide imaging has been recently reported by Lee
et al.
(Fig. 42.5).
They hypothesized that solid nanoparticles composed of perox-
alate polymers, which encapsulated fluorescent dyes, would chemi-
luminesce under aqueous conditions in the presence of hydrogen
peroxide and also be suitable for
in vivo
imaging of hydrogen per-
oxide. Novel polymers were rationally designed, incorporating the
peroxalate ester groups in the polymer backbone. They were syn-
thesizedfromthereactionofoxalicchloride,hydroxybenzylalcohol,
and octanediol. The optimal composition of three monomers was
chosen from the careful consideration of the reactivity to hydrogen
peroxide and stability against water hydrolysis. Chemiluminescent
nanoparticles were prepared by a single-emulsion method, and flu-
orescent dyes were encapsulated during the nanoparticles' forma-
tion. The peroxalate particles had a mean sizeof 550 nm.
11
Theperoxalatenanoparticlesexhibitedseveralattractiveproper-
ties for
in vivo
imaging, such as tunable wavelength emission, excel-
lentsensitivity,andhighspecificityforhydrogenperoxideoverother
ROS. As shown in Fig. 42.6, chemiluminescent intensity increased
linearly withthe concentration of hydrogen peroxide.
They could detect hydrogen peroxide as low as 250 nM. The
chemiluminescent intensity of the peroxalate nanoparticles in the
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