A 20 MHz 33220A function/arbitrary waveform generator (Agilent Technologies Inc., Santa Clara, CA, USA) was used to drive the coils. Amplification of this input signal was performed using a 1000 W RF power amplifier, model 1140LA (Electronics & Innovation Ltd., Rochester, NY, USA). The amplified signal runs through the L-matching circuit that enables maximum power transfer from the source to load (coil). Since the coil dissipates heat due to resistive losses, a Masterflex® peristaltic pump circulates water through the instrument’s body to remove excess heat. A simple air-cooled heat exchanger configuration maintains the circulating water at a constant temperature of about 24 °C to avoid the temperature increasing throughout the duration of the experiment. Temperatures of the test samples (e.g. cells, MNPs) and surroundings were monitored with a FOTEMP-PLUS signal conditioner using TS3–10 mm-06 fiber optic temperature sensors (Optocon AG, Dresden, Germany) and stored in a computer using the FOTEMP-ASSISTANT 2.3 configuration and data logging software, also from Optocon AG. The temperature of the samples was measured by passing the fiber optic thermal sensor through a lid with a hole and the surrounding temperature was measured by placing another fiber optic sensor close to the plate. The reusable lid was cleaned with ethanol after each run to avoid contamination. Subsection E in Supplementary Information shows top-view and side-view of the samples placed on the devices (see figure S9 and figure S10), as well as an example of the temperatures reached during MFH (see figures S11 and S12).
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