Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

pH Sensor for Cell Organelles

14.12.2012
pH-dependent conformation change controls energy transfer in nanocrystal sensors

Acidity (pH) and its changes play an important role in many physiological processes, including protein folding, and can act as indicators of cancer. In the journal Angewandte Chemie, American researchers have now introduced an unconventional pH sensor that makes it possible to monitor changes in pH values in living cells over longer periods of time, with previously unobtainable spatial resolution. This is possible through the combination of fluorescent nanocrystals with mobile molecular “arms” that can fold or unfold depending on the pH of their environment.



Endosomes, cell organelles that play a role in transport within cells, experience a considerable drop in their pH value as they mature. This was observed by the team working with Moungi G. Bawendi at the Massachusetts Institute of Technology (MIT) in Cambridge (USA) by using a new nanoscopic pH sensor and a fluorescence microscope.

The secret to their success lies in the unconventional design of their sensor: A mobile molecular “arm” connects a green fluorescent nanocrystal to a red fluorescent dye. The nanocrystals are particles of semiconductor materials that easily transfer the light energy they absorb to fluorescent dyes through a radiation-free mechanism (fluorescence resonance energy transfer, or FRET). This causes the dye to fluoresce—as long as both of the FRET partners are close enough to each other.

The distance between the nanocrystal and the dye is controlled by folding and unfolding of the molecular arm on the nano pH sensor—and this motion is pH-dependent. The arm consists of one piece of double-stranded and one piece of single-stranded DNA. As the concentration of H+ ions increases, so does the tendency to form a “triple strand”, in which the single strand fits into the groove of the double strand, causing the arm to fold. This “arm movement” takes place in the physiologically important range around pH 7 and is very sensitive to the slightest change.

At higher pH values, the arm is stretched out and the FRET partners are too far away from each other for energy transfer to occur. The nanocrystal emits green fluorescence and the dye does not fluoresce. As the pH gets lower, the arm folds enough to allow FRET energy transfer. The green fluorescence of the nanocrystal decreases and the dye begins to glow red. Because this technique measures the ratio of green to red fluorescence instead of an absolute value, variations in intensity make no difference. The sensor thus has an internal reference.

In this type of sensor, the actual “pH tester” and the optical signaling device are two separate components. By replacing the pH tester with a molecular arm that responds to a different analyte it should be possible to use the same principle and the same optical signaling device to build sensors for other target molecules.

Nanocrystal fluorophores have caused much excitement in several fields because of their attractive optical properties. Nanocrystals offer superior properties compared to traditional molecular fluorophores, in particular in biology, where they can help reveal the inner workings of the cell. However, converting these new nanomaterials into fluorescent sensors has proven difficult. The concept of harnessing a molecular conformational change to create a sensor is new for nanocrystal sensors and could prove a general solution to the problem of making sensors from nanocrystals.

Author: Moungi G. Bawendi, Massachusetts Institute of Technology, Cambridge (USA), http://nanocluster.mit.edu/people.php

Title: Conformational Control of Energy Transfer: A Mechanism for Biocompatible Nanocrystal-Based Sensors

Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201207181

Moungi G. Bawendi | Angewandte Chemie
Further information:
http://nanocluster.mit.edu/people.php
http://pressroom.angewandte.org

More articles from Life Sciences:

nachricht Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory

nachricht Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>