A Thermal Cycler Based on Magnetic Induction Heating and Anti-Freezing Water Cooling for Rapid PCR

Abstract

Distinguished by its exceptional sensitivity and specificity, Polymerase Chain Reaction (PCR) is a pivotal technology for pathogen detection. However, traditional PCR instruments that employ thermoelectric cooling (TEC) are often constrained by cost, efficiency, and performance variability resulting from the fluctuations in ambient temperature. Here, we present a thermal cycler that utilizes electromagnetic induction heating at 50 kHz and anti-freezing water cooling with a velocity of 0.06 m/s to facilitate rapid heating and cooling of the PCR reaction chamber, significantly enhancing heat transfer efficiency. A multi-physics theoretical heat transfer model, developed using the digital twin approach, enables precise temperature control through advanced algorithms. Experimental results reveal average heating and cooling rates of 14.92 °C/s and 13.39 °C/s, respectively, significantly exceeding those of conventional methods. Compared to commercial PCR instruments, the proposed system further optimizes cost, efficiency, and practicality. Finally, PCR experiments were successfully performed using cDNA (Hepatitis B virus) at various concentrations.

Keywords: anti-freezing water cooling; magnetic induction heating; polymerase chain reaction; rapid heat transfer; thermal cycler.

Figure 1

Illustration of MIH and AWC-based thermal cycler. (a) Schematic diagram depicting the heat resistance of conventional thermoelectric (TEC) systems, $R_1$ is the contact thermal resistor between the PCR chamber and Silicone Grease, $R_2$ is the contact thermal resistor between Silicone Grease and Peltier’s upper surface, $R$ is the complex thermal resistor of TEC, $R_3$ is the contact thermal resistor between Peltier’s lower surface and Silicone Grease, and $R_4$ is the contact thermal resistor between Silicone Grease and Heat sink; (b) Schematic diagram illustrating the heat resistance characteristics of our proposed design, $R_w$ is the complex thermal resistor of AWC, $R_m$ is the thermal resistor of MIH; (c) Performance comparison plots between the TEC and ours; (d) 3D conceptual representation of the proposal cycler; (e) Photograph of the thermal cycler. Mineral oil is added into the PCR tube to prevent water evaporation, and temperature is monitored in real-time by a PT100 sensor and regulated using a proportional-integral-derivative (PID) control algorithm.

Figure 2

Illustration of the MIH and AWC-based qPCR device. (a) 3D conceptual diagram of the qPCR device; (b) Schematic diagram of the Control module; (c) Schematic diagram of the Optical detection module.

Figure 3

Simulation and experimental results during the magnetic induction heating. (a) FEA model of the PCR control device; (b) Distribution of flux density of the induced magnetic field; (c) FEA results showing temperature variation during induction heating; (d) Thermography illustrating the PCR chamber induction heating process; (e) Relationship between different excitation frequencies and temperature; (f) Impact of coil turns on temperature; (g) Effect of the gap between the PCR chamber and coil on temperature; (h) Influence of electrical current on temperature.

Figure 4

COMSOL cooling simulation results. (a) Initial cooling state; (b) Temperature of velocity field distribution at 3 s; (c) Fluid temperature field at 5 s; (d) Temperature of velocity field distribution at 14 s; (e) Effect of water velocity on temperature; (f) Relationship between the initial cooling water temperature and chamber temperature.

Figure 5

Temperature curves: (a) Three setpoints (45–72–95 °C); (b) Two setpoints (45–95 °C); (c) A complete PCR controlling program.

Figure 6

PCR Test Performance. (a) Testing different concentrations using the proposed PCR device; (b) Testing different concentrations using the commercial PCR device; (c) Linearity assessment of the proposed PCR device compared with the commercial PCR device.