Self-assembly and chains of rotating magnetic particles

October 26, 2010 By Adarsh Sandhu
Dr Park and Fig. 1: Experimental procedure for homogenous biosensing protocol based on chains of self-assembled magnetic particles rotating in solution. Copyright : Toyohashi University of Technology

Dr. Park and colleagues report on a new biosensing protocol based on monitoring changes in optical transmittance of a solution containing self-assembled chains of functionalized magnetic beads being rotated by an external magnetic field.

Biosensing based on the detection of magnetic labels offers a rapid, sensitive and inexpensive protocol for point-of-care medical diagnostics, where magnetoresitive are used to detect magnetic beads immobilized onto substrates via biorecognition processes.

However, this approach necessitates multiple steps – immobilization of probe molecules, washing to remove non-specific binding, and so on – constraints which limit the sensitivity, speed and cost, and ultimately the size of the system.

In an alternative approach Sang Yoon Park at the Electronics Inspired Interdisciplinary Research Instiute (EIIRIS), Toyohashi Tech and colleagues at Tokyo Institute of Technology, report on a new protocol based on monitoring changes in optical transmittance of a solution containing self-assembled chains of functionalized magnetic beads being rotated by an external . Importantly, this so-called homogenous method is rapid, highly sensitive over a wide range of concentration and does not require substrates or magnetic sensors.

The lengths of chains of biotinylated magnetic beads rotating in a solution increased with the addition of complementary biomolecules (avidin) to the solution, and importantly, the increase in chain length was directly related to the concentration of avidin added to the solution. This change in the length of the chains was measured with high accuracy by monitoring changes in the optical transmission of the rotating chains in the solution. Notably, optical transmittance through the solution depended on the lengths of the rotating chains, which in turn was related to the concentration of avidin molecules added to the solution.

The experimental set-up consisted of three simple components: a light source of a non-polarized white beam, a cuvette containing a solution of functionalized magnetic beads, and a compact spectrometer. The biotinylated magnetic beads used by the researchers had a diameter of 250 nm, and consisted of superparamagnetic particles embedded into a polymer matrix. The polymer surface was covered with biotin biomolecules and the concentration of avidin added to the solution was measured by applying a rotating magnetic field to the cuvette and monitoring optical transmission of the solution when the target molecule (avidin) was added to the solution.

In 30 seconds, the researchers quantitatively determined the concentration of avidin added to the solution with a sensitivity of 100 pM and a dynamic range of at least four orders of magnitude. This protocol is a rapid, highly sensitive, inexpensive and homogeneous means for quantifying biorecognition processes.

Explore further: Philips demonstrates magnetic biosensors for high-sensitivity molecular diagnostics

More information: Nano Letters 10 446 (2010) DOI:10.1021/nl9030488

Related Stories

Detecting Cancer with Silica Nanoparticles

September 18, 2006

Tumor necrosis factor-alpha is a widely accepted biomarker for cancer, but the minute amounts of this protein circulating in blood makes detecting the molecule and measuring its concentration accurately a technological challenge.

Detecting Disease

February 14, 2007

Analyzing human blood for a very low virus concentration or a sample of water for a bioterrorism agent has always been a time-consuming and difficult process. Researchers at the Georgia Institute of Technology and Emory University ...

Optical sensors make MRI scans safer

September 18, 2008

( -- Magnetic resonance scans will be safer for children and other patients needing anaesthesia, thanks to new kinds of optical sensors developed by a team of European researchers.

Recommended for you

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

New sensor sends electronic signal when estrogen is detected

November 24, 2015

Estrogen is a tiny molecule, but it can have big effects on humans and other animals. Estrogen is one of the main hormones that regulates the female reproductive system - it can be monitored to track human fertility and is ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.