Magneto-optic biosensors enabled by bio-functionalized magnetized nanoparticles, which are sensitive, fast, cost-effective and capable of utilization by relatively untrained personnel, for example, in an effort to combat bio-terrorism and for point-of-service biomedical applications, have been developed by Argonne National Laboratory (ANL) scientists Seok-Hwan Chung, Axel F. Hoffmann and Samuel D. Bader.
Chung, Hoffmann and Bader have compared their magneto-optic biosensor sensitivity to that of a commercially available magneto-electric measurement system. A significant advantage of the ANL magneto-optic method is that the technique is able to detect, for example, three orders of magnitude fewer particles within a confined region in a relatively short time. Further, in addition to the small sample requirement, the easy optical access to the micro-fluidic system enables potential lab-on-a-chip applications for viscosimetry and biosensing.
According to U.S. Patent 7,639,359, Argonne National Laboratory magneto-optic biosensors using bio-functionalized magnetic nanoparticles work when an external magnetic field is applied to a suspension of magnetic nanoparticles. A linearly polarized incident light from a micro-laser is applied to the suspension of magnetic nanoparticles. A photocurrent from polarized light scattering by bio-functionalized magnetic nanoparticles in liquid is detected and analyzed.
The applied magnetic field causes field induced optical anisotropy originating from internal optical anisotropies, and surface or shape anisotropies of individual nanoparticles. Such anisotropy in magnetic nanoparticles causes dichroism and birefriengence of linearly polarized incident light, which are used to sense the changes of Brownian relaxation upon biological bindings in liquid environments.
The magneto-optic sensing technique is applied to a micro-fluidic channel for rapid and sensitive detection with a small sample amount, and subsequent magnetic separation for detoxification. This technique is used for the detection of Brownian relaxation with time sweep as well as frequency sweep.
The biosensor is a magneto-optical sensor that enables rapidly detecting changes in local dynamic properties of the magnetic nanoparticles in liquids. Further magnetic modulation of ferromagnetic particles in liquid potentially increases the signal sensitivity by several orders of magnitude as compared to the known or conventional ac magnetic susceptibility measurements. A possibility exists for in-vitro applications, such as detection of local temperature and viscoelasticity within inter-cellular environments.
Magnetic nanoparticles are receiving increased attention recently due to both fundamental scientific interest and their potential applications in magnetic data storage, actuators, and biosensors. The long-range interaction between magnetic nanoparticles and an external magnetic field enables manipulation and sensitive detection of those particles for such applications.
Also the recent development of bio-conjugated magnetic nanoparticles provides various opportunities for the application of magnetic nanoparticles in the biomedical field. The shelf-life of magnetic nanoparticles can be essentially infinite, which is beneficial compared to other materials for biosensing such as fluorescent and radioactive materials.
In particular, the use of magnetic labels for sensing applications has generated widespread research efforts. In most conventional substrate-based sensing schemes, the absence or presence of magnetically labeled targets is verified via the detection of the magnetic stray field by means of the giant magnetoresistance, anisotropic magnetoresistance, Hall effect or superconducting quantum interference devices.
Among recent developments is a substrate-free biosensing approach based on Brownian relaxation of magnetic nanoparticles with biological surfactant suspended in liquid. This approach relies on detecting the modification of the Brownian motion of magnetic nanoparticles when they bind to selective targets in liquid solutions.
In particular, the use of magnetic labels for sensing applications has generated widespread research efforts. In most conventional substrate-based sensing schemes, the absence or presence of magnetically labeled targets is verified via the detection of the magnetic stray field by means of the giant magnetoresistance, anisotropic magnetoresistance, Hall effect or superconducting quantum interference devices.
Among recent developments is a substrate-free biosensing approach based on Brownian relaxation of magnetic nanoparticles with biological surfactant suspended in liquid. This approach relies on detecting the modification of the Brownian motion of magnetic nanoparticles when they bind to selective targets in liquid solutions.
FIG. 1 is a schematic diagram representation illustrating a magneto-optic biosensor
FIG. 2 is a schematic and block diagram representation illustrating exemplary apparatus for implementing a magneto-optic biosensor
Chung, Hoffmann and Bader experimentally demonstrated a magneto-optic measurement of Brownian relaxation of magnetic nanoparticles suspended in liquid. They have applied the magneto-optic sensing technique to a micro-fluidic channel with rapid and sensitive detection with a small sample amount, and subsequent magnetic separation for detoxification. We have determined that this technique can be used for the detection of Brownian relaxation with time sweep as well as frequency sweep.
