(391b) Microfluidic Capturing and Detection Dynamics of a Magnetic Nanoparticle Based Biosystem

Microfluidics combined with nanotechnology is playing a key role in transforming conventional biological work into Lab-on-chip devices; devices in which the entire analysis of a sample can be performed at the site of interest, including separation, and detection. These devices are now being realized for medical diagnostics in the hospital, forensic analysis of DNA at site of crime, and environmental analysis at a pollution site. Recently, Magnetic force methods are combined with microfluidic approach for on-chip separation and detection of biomolecules. These methods are based on manipulating the chemical or biological target molecules by attaching it to magnetic carriers and using an external magnetic field. However, most of the recent developments made in this area is based on functionalized magnetic beads or microparticles, there are relative few microfluidic systems developed that have employed magnetic nanoparticles. Compared with magnetic microparticles or microbeads, magnetic nanoparticles offer biocompatibility, stability, higher surface to volume ratio, minimum disturbance caused due to attached biomolecules, easily modifiable surfaces and moreover they are superparamagnetic.

While the selectivity and the specificity of attaching target molecule to magnetic carrier are related to the surface functionalization, the efficiency of the magnetic manipulation in microfluidics involves interplay of various other parameters such as inlet velocity of fluid containing magnetic nanoparticles, size of nanoparticles, magnetic field strength and its orientation, geometry of the device etc. In order to provide more quantitative comprehension of separation and detection of biomolecules using magnetic nanoparticles in microfluidic system and consequently help in designing, optimizing and developing more robust, efficient microfluidic lab-on-chip devices, finite element models are developed both for predicting the transport and capture of magnetic nanoparticles in a microfluidic system as well as for quantifying the effect of convection, diffusion, and magnetic field on the surface based detection.

The trajectories and trapping efficiencies were calculated and it was demonstrated that not only the size but also the point of release of nanoparticles within the microchannel affects the separation process. Influence of three important parameters, inlet velocities of fluid, diameter of magnetic nanoparticles and magnetic field strength on the trapping efficiency were investigated and optimized values of inlet velocity and magnetic field strength for the simulated system were predicted. It was further demonstrated that the angular position of magnet around the microchannel is also critical in dictating the resulting bioseparation performance. The efficiency of detection process greatly depends on kinetics and dynamics of surface-binding reaction between the target analyte and surface bound probes. The target molecules when tagged with magnetic nanoparticles were efficiently focused on the sensing site due to magnetic force which resulted in enhanced mass transport, faster binding, and consequently considerable reduction in detection time of target molecules when compared with physical micromixing.

The simulation performed using the developed models at the concept stage provided an excellent estimate of the potential to use magnetic nanoparticles for integrated surface-based bioassays. It can also help to investigate a wide range of design parameters and consequently predict an optimized and efficient design of these devices.