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8/6/2006 8:20:01 AM
Nanoparticle pH Meters

Having the ability to measure pH in a tissue without the need for a biopsy could provide clinicians with a rapid method for determining if a suspicious growth is malignant. Two novel nanoparticles raise the distinct possibility that making such measurements could soon be reality.

At Denmark’s Risø National Laboratory, Anne Marie Scharff-Poulsen, Ph.D., and her colleagues have created a polymer nanoparticle containing two fluorescent dyes. One of the dyes is sensitive to pH changes, while the other is not, and both are chemically attached to the polymer chains that make up the nanoparticle. Using the two dyes provides an internal standard that increases the accuracy and sensitivity of pH measurements – a change in the relative fluorescent emissions of the two dye molecules provides an absolute measurement of pH.

The investigators demonstrated that this nanosensor is capable of measuring pH from 5.8 to 7.2. This range is well within limits relevant for cancer detection or for use in laboratory studies aimed at better understanding cancer cell biology. The researchers published their work in the journal Chemistry of Materials.

In a second report, published in the journal Nano Letters, Naomi Halas, Ph.D., and her collaborators at Rice University describe their use of gold-coated silica nanoshells as miniature pH meters. To form their pH meter, the investigators coated the nanoshells with the pH-sensitive molecule para-mercaptobenzoic acid (pMBA).

When placed in solutions of varying acidity and illuminated, the nanoshell-molecule device provides small but easily detectable changes in the properties of the scattered light. Software that the team developed decodes the light-scattering data, yielding a direct measurement of the pH of the nanodevice's local environment to remarkably high accuracy. Inspired by techniques normally applied to image recognition, the team formulated an efficient statistical learning procedure to produce the device output, achieving an average accuracy of 0.1 pH units between pH 5.8 and 7.6.

The work on fluorescent pH-sensitive nanoparticles is detailed in a paper titled, “Synthesis and characterization of ratiometric, pH sensing nanoparticles with covalently attached fluorescent dyes.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.

View abstract.

Other Headlines from NCI Alliance for Nanotechnology in Cancer ...
 - Tekmira and the National Cancer Institute Publish Promising Data Demonstrating the Anti-Tumor Activity of a Novel Cancer Target
 - NCI Awards $1.7 Million to Cancer Specialist at Children’s Hospital Los Angeles
 - Nanoparticles Enhance Detection of Circulating Tumor Cells
 - Hand-held NMR Instrument Yields Rapid Analysis of Human Tumors
 - Biodegradable Biopolymer Nanoparticles Hold Promise for Twin Attack on Breast Cancer

More Research Headlines ...
 - Experiments Settle Long-Standing Debate about Mysterious Array Formations in Nanofilms
 - "Critical baby step" taken for spying life on a molecular scale
 - Seeing an atomic thickness
 - First-ever sub-nanoscale snapshots of renegade protein in Huntington's Disease
 - Karlsruhe Invisibility Cloak: Disappearing Visibly

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