Selective Heating of Multiple Nanoparticles
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Selective Heating of Multiple Nanoparticles Andy Wijaya1, Katherine A. Brown2, Joshua D. Alper3, and Kimberly Hamad-Schifferli2,3 1 Chemical Engineering; 3Biological Engineering Division, and 3Mechanical Engineering; Massachusetts Institute of Technology, Cambridge, MA 02139 U.S.A. ABSTRACT A method for heating multiple types of magnetic nanoparticles independently is described. This technique exploits tuning of the size and material dependent properties of magnetic field heating of nanoparticles to allow independent heating by application of the field at different frequencies. Magnetic field heating experiments as a function of field frequency show that there is potential for this technique in vitro. INTRODUCTION Magnetic nanoparticles have been utilized for numerous biological applications, such as sensing, [1, 2], separation[3], drug delivery[4]. In particular, magnetic nanoparticles have found clinical application in hyperthermia for cancer treatment[5]. In this process, magnetic nanoparticles are injected near the site of a tumor or targeted via antibodies. Application of external magnetic fields heat the nanoparticles, raising the temperature of the tumor, burning it. Typically this has been achieved by using one type of nanoparticle, usually iron oxide. We explore here the possibility of using different types of nanoparticles that can differ in size or material, which can be heated independently at different magnetic field frequencies. This would enable greater flexibility in magnetic field heating applications. EXPERIMENTAL DETAILS Iron oxide nanoparticles were synthesized by literature methods [6, 7] or purchased (FerroTec, USA). Fe doped Au nanoparticles were synthesized according to a modification of literature Au nanoparticle synthesis [8] and functionalized with the ligand bis (p-sulphonatophenyl) phenylphosphine dihydrate, dipotassium salt (BPS). Nanoparticles were concentrated to high concentrations in water by salt precipitation in combination with lyophilization. Fe doped Au nanoparticles were at a final concentration of 3.7µM. Fe3O4 nanoparticles were at 3.9% volume fraction as received. Approximately 100 µL of the nanoparticle solutions were placed in a coil of 25 turns. Alternating magnetic fields were generated by supplying a current from a signal generator and amplified by a 100W amplifier. The temperature of the solution was measured by a thermocouple placed in the solution. Custom built software was used to control data acquisition. DISCUSSION Magnetic field heating of superparamagnetic nanoparticles is described by the power loss equation[9, 10] 2 ( mHωτ eff ) (1) P= 2 2τ eff k BTV 1 + ω 2τ eff
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where m is the magnetic moment per particle, ω the field frequency, V the nanoparticle volume, and teff the effective relaxation time. τeff depends on both Néel (τN)and Brownian (τB) relaxation losses by τ τ τ eff = N B (2) τ N +τ B where the timescale of Brownian relaxation losses is 8πηRH3 (3) τB = k BT and η is the sample viscosity and RH the particle hydrodyna
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