Rice scientists make first nanoscale pH meter

Jun 29, 2006

Using unique nanoparticles that convert laser light into useful information, Rice University scientists have created the world's first nano-sized pH meter.

The discovery, which appears online this week in the journal Nano Letters, presents biologists with the first potential means of measuring accurate pH changes over a wide pH range in real-time inside living tissue and cells.

"Almost every biologist I speak with comes up with one or two things they'd like to measure with this," said lead researcher Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering, professor of chemistry and director of Rice's Laboratory for Nanophotonics (LANP).

For example, pH may be useful in determining whether or not some cancer tumors are malignant. With current methods, a piece of the tumor would need to be physically removed via biopsy - a painful and invasive procedure - and visually evaluated under a microscope. Halas said LANP's new nano-pH meter could be used instead as an "optical biopsy" to measure the pH inside the tumor with nothing more invasive than an injection.

Halas's LANP team created the pH sensor using nanoshells, optically tuned nanoparticles invented by Halas. Each nanoshell contains a tiny core of non-conducting silica that's covered by a thin shell of metal, usually gold. Many times smaller than living cells, nanoshells can be produced with great precision and the metal shells can be tuned to absorb or scatter specific wavelengths of light.

To form the pH sensor, Halas' team coated the nanoshells with pH-sensitive molecules called paramercaptobenzoic acid, or 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 that, when "decoded," can be used to determine 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.

The term "pH" was coined by the Danish chemist Søren Sørensen in 1909 as a convenient way of expressing a solution's acidity. pH ranges from one - the most acidic - to 14 - the most alkaline.

Co-authors on the paper include postdoctoral researchers Sandra Bishnoi, now an assistant professor at the Illinois Institute of Technology, and Muhammed Gheith; graduate students Christopher Rozell and Carly Levin; Bruce Johnson, distinguished faculty fellow of chemistry and executive director of the Rice Quantum Institute; and Don Johnson, J.S. Abercrombie Professor of Electrical and Computer Engineering and Statistics.

Source: Rice University

Explore further: Physicists create new nanoparticle for cancer therapy

add to favorites email to friend print save as pdf

Related Stories

Solar-powered sterilization technology

Jul 22, 2013

Rice University nanotechnology researchers have unveiled a solar-powered sterilization system that could be a boon for more than 2.5 billion people who lack adequate sanitation. The "solar steam" sterilization system uses ...

Bovine blood keeps gold nanoparticles stable

May 14, 2013

(Phys.org) —A protein from cow blood has the remarkable ability to keep gold nanoparticles from clumping in a solution. The discovery could lead to improved biomedical applications and contribute to projects ...

Hot electrons do the impossible in catalytic chemistry

Dec 17, 2012

(Phys.org)—From petroleum refining to food processing, the vast majority of commercial chemical applications involve catalysts to control the rate of chemical reactions. Anything that can increase the efficiency ...

Recommended for you

Physicists create new nanoparticle for cancer therapy

Apr 16, 2014

A University of Texas at Arlington physicist working to create a luminescent nanoparticle to use in security-related radiation detection may have instead happened upon an advance in photodynamic cancer therapy.

User comments : 0

More news stories

Wiring up carbon-based electronics

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...