## 2 Experimental Section  
In this study, we used water-based ferrofluid containing superparamagnetic nanoparticles classified into the three types of EMG1111, EMG707 and EMG607 (Ferrotec, Japan) in line with different surface treatments. Table 1 shows characteristics of magnetic nanoparticles used in the experiment. The surface of EMG1111 nanoparticles was not modified with any surfactant. In contrast, EMG707 nanoparticles were modified with an anionic surfactant to improve dispersion, and EMG607 nanoparticles were modified with a cationic surfactant. All the superparamagnetic nanoparticles had an average diameter of 10 nm, and were composed of mixtures of magnetite (Fe\({}_{3}\)O\({}_{4}\)) and maghemite (Fe\({}_{2}\)O\({}_{3}\)) iron oxides. \begin{table}
\begin{tabular}{|c|c|c|c|c|} \hline  & **Particle Size** & **Composition** & **Appearance** & **Surface Treatment** \\ \hline
**EMG607** & & & Water-based & Cationic surfactant \\ \hline
**EMG707** & 10 nm & Fe\({}_{3}\)O\({}_{4}\)/Fe\({}_{2}\)O\({}_{3}\) & ferrofluid & Anionic surfactant \\ \hline
**EMG1111** & & & Water-based slurry & No treatment \\ \hline \end{tabular}
\end{table} 
Table 1: Characteristics of magnetic nanoparticles used in the experiment. Figure 1: TEM images and EDS mapping images of EMG1111 magnetic nanoparticles. (**a**) TEM image of isolated magnetic nanoparticles; (**b**) TEM image of magnetic nanoparticles; (**c**) EDS mapping image of iron corresponding to image (b); (**d**) EDS mapping image of oxygen corresponding to image (b). The characteristics of the superparamagnetic nanoparticles used in the experiments were examined using a transmission electron microscope (TEM) (JEM-2200 FS, JEOL) and an energy-dispersive X-ray spectrometer (EDS) (JED-2300T, JEOL), as shown in Figure 1. The magnetic particle fluids were centrifuged to remove excess surfactant molecules. Additionally, the magnetic nanoparticle fluids were diluted to a certain concentration with distilled water, and the magnetic nanoparticles were then dispersed using ultra sonication. Experimental PCR amplification is outlined here. The strain used in this study was _Escherichia coli_ DH5a cultivated in LB medium. Cells were harvested by centrifugation and suspended in TEN buffer (10 mM Tris-HCl, pH 8.0, 1 mM EDTA, 100 mM NaCl), and 0.3 g of glass beads were added. The cells were broken by being shaken for 10 min on a vortex mixer at maximum speed, and nucleic acid was extracted through phenol/chloroform treatment and ethanol precipitation. An approximately 1,500-bp segment of the 16S rRNA gene was amplified by PCR with the forward and reverse primers 5'-AGA GTT TGA TCC TGG CTC AG-3' (positions 8-27 according to _Escherichia coli_ numbering) and 5'-GGC TAC CTT GTT ACG ACT T-3' (positions 1510-1492) using an Ex Taq polymerase kit (TaKaRa). PCR thermal cycling was carried out in 0.2-ml reaction tubes in a QuickBath QB-0225A unit (ThermoGen Inc.). Amplification was performed in the following 50-\(\upmu\)L mixture: 5.0 \(\upmu\)L of 10 \(\times\) Ex Taq PCR buffer, 4.0 \(\upmu\)L of dNTP mixture (dATP, dTTP, dGTP and dCTP; 2.5 mM each), 1.0 \(\upmu\)L of forward primer, 1.0 \(\upmu\)L of reverse primer (10 mM each), 27.5 \(\upmu\)L of distilled water, 0.2 \(\upmu\)L of Ex Taq polymerase (1 U/\(\upmu\)L), 1.0 \(\upmu\)L of template DNA (100 ng of DNA) and 10 \(\upmu\)L of ferromagnetic nanoparticles (EMG607: 0.4-1.8 \(\upmu\)L; EMG707: 0.04-0.18 \(\upmu\)L; EMG1111: 0.02-0.12 \(\upmu\)L). The thermal profile for amplification began with an initial denaturation step (2 min, 96 \({}^{\circ}\)C) followed by 25 cycles of denaturation (20 s, 96 \({}^{\circ}\)C), annealing (20 s, 56 \({}^{\circ}\)C) and extension (90 s, 72 \({}^{\circ}\)C), then a final terminal extension step (2 min, 72 \({}^{\circ}\)C). Aliquots of 5.0 \(\upmu\)L from PCR were analyzed using agarose gel (1.2%) electrophoresis, and the product yield was confirmed using the InGenius system (Syngene).