## 1 Introduction  
The polymerase chain reaction (PCR) is a technique that allows reproduction and amplification of specific DNA segments using DNA polymerase _in vitro_[1]. Currently, the PCR method is widely used in genetic technology, bioscience, diagnosis therapy, medicine development and personal identification. Recently, it has been reported that PCR efficiency is improved by nanoparticles such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon nanopowder, metallic nanoparticles and nonmetallic nanoparticles [2; 3; 4; 5]. Among the variety of nanoparticles used, gold nanoparticles have been reported to have an outstanding effect on PCR efficiency. [PERSON] _et al._[6] reported that such nanoparticles inhibited nonspecific products in PCR at low annealing temperatures. [PERSON] _et al._[7] also reported that PCR efficiency was dramatically increased by using gold nanoparticles in PCR reagents. They speculate that the outstanding heat transfer properties of gold nanoparticles would enhance PCR efficiency and shorten reaction times. However, there have been a number of contradictory reports stating that gold nanoparticles have remarkably negative effects on PCR efficiency. [PERSON] _et al._[8] reported that they could inhibit PCR efficiency at high levels of concentration, and suggested a complex interaction between gold nanoparticles and the Taq polymerase DNA synthetic enzyme. [PERSON] _et al._[9] concluded that the surface interaction between gold nanoparticles and polymerase, rather than the DNA template or primers, inhibited PCR efficiency. They also demonstrated that the effects of gold nanoparticles on PCR could be reversed by increasing polymerase concentration or by adding bovine serum albumin (BSA) as a competitive displacer. [PERSON] _et al._[10] suggested that larger gold nanoparticles have a stronger inhibitory effect on PCR than smaller ones at the same particle concentration. According to their reports, the interaction between Taq polymerase and nanoparticle surfaces is one of the most significant factors in inhibiting PCR efficiency. The mechanism of PCR efficiency enhancement by several types of nanoparticles is currently attracting attention as a possible future-generation PCR technique using nanoparticles. However, so far, there have been no reports on the effects of magnetic nanoparticles on PCR efficiency. Like gold nanoparticles, magnetic nanoparticles are dispersed in a solvent, forming a colloidal system. They have outstanding magnetic properties, and are classified into two types: ferromagnetic and paramagnetic/superparamagnetic. As ferromagnetic systems are magnetized, the particles tend to aggregate and form clusters, while paramagnetic/superparamagnetic systems remain stable in the absence of an external magnetic field [11; 12; 13]. The structure and magnetization of ferromagnetic and paramagnetic particles can be changed by applying external magnetic fields [14; 15; 16]. Also in the same way as gold nanoparticles, the surface of magnetic nanoparticles can be modified with a variety of chemicals and biomolecules. [PERSON] _et al._[17] leveraged the physical and chemical properties of magnetic nanoparticles, and reported that the enzyme activities of \(\alpha\)-amylase immobilized on superparamagnetic particles increased in a rotational magnetic field. Magnetic nanoparticles can be utilized in the field of bio-nano technology, e.g., in the enhancement of magnetic resonance imaging (MRI), the development of drug delivery systems (DDSs), diagnosis therapies such as hyperthermia, and the labeling of tumor cells [18; 19; 20]. In this paper, we report on the effects of superparamagnetic nanoparticles on PCR amplification without an external magnetic field. We focus not only on the surface interaction between individual magnetic nanoparticles and PCR reagents, but also on the structures of magnetic particle clusterstransformed by heat treatment in conventional PCR thermal cycles.