V. Sudha Rani

Translocation of bio-functionalized magnetic beads using smart magnetophoresis

We demonstrate real time on-chip translocation of bio-functionalized superparamagnetic beads on a silicon surface in a solution using a magnetophoresis technique. The superparamagnetic beads act as biomolecule carriers. Fluorescent-labeled Atto-520 biotin was loaded to streptavidin-coated magnetic beads (Dynabead(®) M-280) by means of ligand-receptor interactions. The magnetic pathways were patterned lithographically such that semi-elliptical Ni(80)Fe(20) elements were arranged sequentially for a few hundred micrometers in length. An external rotating magnetic field was used to drive translational forces on the magnetic beads that were proportional to the product of the field strength and its gradient. The translational force at the curving edge of the pathway element of 6 μm diameter was calculated to be ∼1.2 pN for an applied field of 7.9 kA m(-1). However, the force at the flat edge was calculated to be ∼0.16 pN. The translational force was larger than the drag force and thus allowed the magnetic beads to move in a directional way along the curving edge of the pathway. However, the force was not sufficient to move the beads along the flat edge. The top and bottom curving edge semi-elliptical NiFe pathways were obliquely-arranged on the left and right sides of the converging site, respectively. This caused a central translational force that allowed the converging and diverging of the Atto-520 biotin loaded streptavidin magnetic beads at a particular site.

Translocation of magnetic beads using patterned magnetic pathways for biosensing applications

We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9×4×0.1 μm3) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead® M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the senso...

Template Synthesis of Cobalt Nanowires Using PS-b-PMMA Block Copolymer

Cobalt nanowires with 18 plusmn 5 nm diameter were grown in the self-assembled diblock copolymer templates using electrodeposition technique. The diblock copolymer templates with hexagonally ordered nanoporous structure were successfully synthesized by varying the copolymer thickness from 50 nm to 430 nm and post annealing at temperature 180degC for 24 h. The minimum optimized pore sizes of the template were 18 plusmn 5 nm with well order hexagonal nanoporous structure at copolymer thickness from 350 nm to 430 nm. Cobalt nanowires were then successfully deposited using three electrode configuration potentiostatic electrodeposition methods. To remove the cross linked polystyrene of the template and to display the cobalt nanowires, heat treatment was carried out. The morphology of the templates and cobalt nanowires was observed using Scanning Electron Microscope (SEM). The magnetic properties of the cobalt nanowires are analyzed using Vibrating Sample Magnetometer (VSM).

Fabrication of Nanowire Arrays Using Diblock Copolymer

Electrodeposited Co nanowires were grown on self assembled diblock copolymer nanoporous templates. While keeping the template pore size and electrolyte pH value constant at 13.7 nm and 3.82, respectively, the DC current density (5 mA/cm2 and 50 mA/cm2) and time of deposition (50s, 100s, 150s and 200s) were varied as an attempt to obtain nanowires of varied aspect ratios and morphologies. It was observed that height of the nanowire linearly enhances with the time of the electrodeposition. SEM images of the samples indicate that the template pores were completely filled during deposition when the current density was set 50 mA/cm2. Excess times of deposition produced a thin layer of the deposited material on top of the porous template. Magnetic hysteresis properties of the generated nanowires were examined by vibration sample magnetometry. The loops displayed are highly square with coercivities of few tens of oersteds. The magnetization of the Co nanowires enhances as the height of the wires increases. The results were analyzed to understand the influence of current density on the growth of nanowires.