Abstract:

Metamaterial-based microwave components are among the state-of-the-art heater and sensor designs for microfluidic systems. The miniaturization and energy-focusing abilities of the metamaterial-based components make it possible to adopt microwave components operating at wavelengths in the order of 10 cm for microfluidic systems. Microwave systems are particularly advantageous for point-of-care and high-throughput applications due to their high speed of operation, very low instrumentation cost, ability to selectively and internally heat specimens, and ability of label-free sensing. In this study, the efficiency and behavior of microwave components designed for heating and sensing small volumes in the scale of nanoliters are studied. In the heating behavior, an optimum passivation layer thickness that depends on the permittivity of the chip material is observed. Increasing the permittivity of the chip material increases the optimum passivation layer thickness. For a typical microfluidic environment that uses polydimethylsiloxane as the chip material and a lossy substrate, 37.4% of incoming microwave power is converted to heat within a 3-nL droplet. Increasing the permittivity of the chip material increases the heating efficiency. The sensing performance of the component shows that a 3-nL droplet generates a shift of 330 MHz (11.3%) in the resonance frequency. There is an optimum chip material permittivity that maximizes the shift in the resonance frequency. Increasing the passivation layer thickness reduces the sensitivity. Results provide a guideline for microwave heater and sensor designs in microfluidic platforms.

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