Illuminating Hydrogen Peroxide In Cells | Chemical & Engineering News
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Web Date: April 8, 2008

Illuminating Hydrogen Peroxide In Cells

Chemiluminescent system is sensitive and specific for H2O2
Department: ACS News, Science & Technology
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LUMINESCENT
ng class="imageTitle">LUMINESCENT</strong> The peroxalate group of naphthofluorescein oxalate (left) reacts with H2O2 to form dioxetanedione, which forms a charge complex to excite the dye.
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LUMINESCENT
ng class="imageTitle">LUMINESCENT</strong> The peroxalate group of naphthofluorescein oxalate (left) reacts with H2O2 to form dioxetanedione, which forms a charge complex to excite the dye.

Hydrogen peroxide is overproduced in cells as part of chronic inflammatory diseases such as heart disease and arthritis, so detecting the molecule in the body is of keen interest for diagnosing and tracking medical conditions. Researchers are also interested in the role of H2O2 in cellular signal transduction. Now, a three-part chemiluminescent system may illuminate H2O2 in cells and tissues.

Detecting H2O2 in vivo is not easy. Its combined low concentration and low reactivity relative to other oxygen species such as superoxide make it difficult to find a sensitive, specific sensor. In a presentation this week before the Division of Physical Chemistry at the ACS national meeting in New Orleans, Niren Murthy of Georgia Institute of Technology described H2O2-sensing nanoparticles composed of a peroxalate-containing polymer and a fluorescent dye such as pentacene (Nat. Mater. 2007, 6, 765).

In solution, H2O2 reacts with the peroxalate component of the polymer to produce dioxetanedione. The dioxetanedione then chemically excites the dye, leading to chemiluminescence of the nanoparticles. The reaction is specific for H2O2; superoxide or the hydroxyl radical will not produce the dioxetanedione.

Experiments with the particles in vitro indicated they can detect H2O2 concentrations down to 250 nM. Murthy and coworkers were also able to detect hydrogen peroxide produced in the peritoneal cavity of mice in response to an injection of a lipopolysaccharide, which induces an immune response.

"This is an exciting development that may overcome problems with the in vivo detection of H2O2," says Henry J. Forman of the University of California, Merced. He adds that for detecting disease pathology, "the specificity for H2O2 and limit of detection in whole animals appear to be very suitable," although the sensitivity might not yet be low enough to detect smaller amounts of H2O2 produced in physiological signal transduction.

Murthy noted that the nanoparticles, about 500 nm in diameter, are probably too large to be of use clinically, so the group is now working on adapting the approach to smaller delivery systems. One of those strategies involves incorporating a fluorescent dye and diphenyl oxalate into a polyethylene glycol micelle about 35 nm in diameter. Although the group hasn???t yet experimented with putting the micelles into mice, lab tests demonstrate that the micelles are even more sensitive than the nanoparticles and can detect H2O2 concentrations as low as 50 nM. Another approach involves covalently attaching the peroxalate ester to a commercially available dye, naphthofluorescein, to make naphthofluorescein oxalate. The compound is unstable in aqueous solution, so Murthy and colleagues are now trying to improve its stability and H2O2 sensitivity.

 
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