Design and realization of magnetic nanoparticles detector based on the nonlinear magnetization

Magnetic nanoparticles have been widely used in the field of biotechnology and medicine, which has a great importance to precise and quantitative detection. This paper introduces a magnetic nanoparticles detection device of low cost, high sensitivity and real-time. When the diameter of the magnetic nanoparticles is 20nm, the third harmonic intensity of the induced voltage is in the level of microvolt, and the larger the mass of the magnetic nanoparticles is, the greater the induced signal strength will be. In addition, there is a linear relation between them. The device can distinguish 18ug of magnetic nanoparticles. Introduction The application of magnetic nanoparticles in the field of life science started a decade ago[1], of which the special magnetic and binding properties make it widely used in the magnetic detection technology and put forward magnetic detection technology. The vitro methods of the detection of magnetic nanoparticles are atomic absorption spectrometry [2], electron paramagnetic resonance [3], and inductively coupled plasma mass spectrometry [4]. The methods of quantitative measurement of concentration of the magnetic nanoparticles by measuring the magnetic response in alternating magnetic field are susceptometry and relaxometry. Susceptometry, which lock-in detects the response in a certain frequency oscillating magnetic field, has high sensitivity of quantitative measurement of the concentration of the magnetic nanoparticles but without selectivity, so other paramagnetic substances may influence the measurement result. Relaxometry gets the concentration of magnetic nanoparticles by measuring the magnetic response of the magnetic nanoparticles in a radio frequency pulsed magnetic field and related calculations. Relaxometry can distinguish between bound and unbound magnetic nanoparticles, for bound nanoparticles recovering from pulse magnetic field according to Neel relaxation in milliseconds to seconds while unbound nanoparticles follow Brown relaxation in a microsecond scale. The SQUID, an expensive and complex cooling device, will be used to measure such short time [5]. The newly developed measurement technology based on nonlinear magnetic properties of magnetic nanoparticles can extract the weak effective signal from the background signal, and measure accurately the high order harmonic component by spectrum analysis method, effectively avoiding the disturbance of the base frequency signal of the background signal.