pISSN 0374-4914 eISSN 2289-0041

## Research Paper

New Physics: Sae Mulli 2006; 52: 564-569

Published online June 1, 2006

## Detection of Magnetic Nanoparticles by Using a Highly Sensitive Spin Valve Bio-Sensor

Sang-Suk LEE1*, Sang-Hyun PARK2 and Kwang-Sup SOH2

1Department of Applied Physics and Electronics Oriental Biomedical Engineering, Sangji University, Wonju 220-702
2Biomedical Physics Laboratory, School of Physics, Seoul National University, Seoul 151-747

Correspondence to:sslee@sangji.ac.kr

### Abstract

We have fabricated a highly sensitive spin valve sensor with high linearity and low hysteresis by using photolithography and an ion-beam-deposition sputtering system. Detection of magnetic nanoparticles by using a giant magnetoresistance spin valve (GMR-SV) bio-sensing device was investigated. The nanoparticles were Co-ferrite magnetic particles coated with a shell of amorphous silica. The average size of a water-soluble bare cobalt nanoparticle was about 9 nm, and the total size, including the amorphous silia shell, was about 50 nm. When a 1 mA sensing current was applied to the current electrode in a patterned active device area of a 2 × 6 $\mu$m$^2$, the output signal of the SV sensor was about 13 mV. In addition, the maximum sensitivity of the fabricated SV sensor was about 0.4 %/Oe. The of output voltage signals and the real-motion images obtained from a four probe magnetoresistive measurement system and a microscope for one liquid drop with a concentration of 2.0 mg/cc were good enough and clear enough to detect the nanopartices inside the de-ionized water.

Keywords: Magnetic nanoparticles, Giant magnetoresistance-spin valve (GMR-SV), Biosensor, Sensing current