Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Stirred, Not Shaken

10.07.2013
Nanoscale magnetic stir bars

Anyone who has ever worked in a laboratory has seen them: magnetic stirrers that rotate magnetic stir bars in liquids to mix them. The stir bars come in many different forms—now including nanometer-sized.



In the journal Angewandte Chemie, researchers from Singapore have now introduced chains made of 40 nm iron oxide particles that act as the world’s smallest magnetic stir bars, effectively stirring picoliter-sized drops of emulsion with a commercial magnetic stirrer.

Effective stirring is essential in chemical and biological experiments. This is usually achieved with magnetic stirrers and stir bars. However, this does not work in the tiny channels and droplets used in lab-on-a-chip applications and for microliter-scale experiments in the biosciences.

Inexpensive stir bars that are small enough but still able to absorb external magnetic energy and efficiently translate it to stir tiny volumes are thus high on the wish list.

The problem lies in the tiny size of previous micrometer-sized stir bars: They are too big to remain suspended because they are pulled to the bottom of the vessel by both gravity and magnetic attraction. At the same time, they are too small to completely stir the solution when they are on the bottom, which works for macroscopic stir bars. The majority of the liquid remains unmixed.

A team led by Hongyu Chen at the Nanyang Technological University in Singapore has now found a solution to this problem: tiny silicon dioxide coated rods made of lined-up iron oxide nanoparticles.

They are even easy to make. Magnetic iron oxide particles with diameters of 40nm are stabilized with oleic acid, modified with citric acid to make them water-soluble, and dispersed in a water/propanol mixture. After addition of an organosilicon compound and ammonia, the reaction vessel is simply left to stand near a magnet overnight. The stir bars can then simply be collected by centrifugation.

The thickness of the silicon layer can be controlled, allowing for the production of stir bars with diameters ranging from 75 nm to 1.4 µm. Their length can reach up to 17 µm. The bars are thus so small that they remain suspended in solution. Addition of a large number of stir bars ensures that all of the liquid is stirred. In the magnetic field of a conventional magnetic stir plate, the individual stir bars move independently. It is thus possible to thoroughly mix droplets of just a few picoliters.

The nanoscale stir bars can be easily removed by adding the droplets on top of a strong magnet wrapped in a layer of plastic film. The magnetic field gradually pulls the stir bars to the bottom of the droplets, and the droplets can then simply be picked up with a pipette.

About the Author
Dr. Hongyu Chen is an Associate Professor in the Division of Chemistry and Biological Chemistry at Nanyang Technological University, Singapore. His main research interest is developing new methodologies for the synthesis of complex nanostructures, and the underlying mechanisms.

Author: Hongyu Chen, Nanyang Technological University, Singapore (Singapore), http://www.ntu.edu.sg/home/hongyuchen/

Title: Stirring in Suspension: Nanometer-Sized Magnetic Stir Bars

Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.20130324

Hongyu Chen | Angewandte Chemie
Further information:
http://pressroom.angewandte.org

More articles from Life Sciences:

nachricht The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences

nachricht Transforming plant cells from generalists to specialists
07.12.2016 | Duke University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

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...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

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

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>