Non-contact detecting solution ionic strength in microfluidic channel utilizing GHz complementary split-ring resonator (CSRR)

This paper presents a novel microchip integrated with a GHz complementary split-ring resonator (CSRR) and a microfluidic channel for non-contact detecting the ionic strength of solutions. An upper C-ring resonator induced with an underneath linear micro-strip is used to generate the complementary resonance. The induced electromagnetic resonance is sensitive to surrounding material properties including complex permittivity and thickness of materials. The insertion loss of the GHz signal increases with the increasing material permittivity nearby the CSRR. Therefore, this technique is good to measure the ionic strength of solutions without using physical electrodes to contact the solutions. Results show that the developed CSRR chip is capable of detecting NaCl solutions of the concentration ranging in 10−3∼5.0 M with a sensitivity of 1.5 dB/M at high concentration range. The CSRR chip is also capable of distinguishing solutions of same concentration but different ionic charges. The developed CSRR chip has shown its potentials for remote monitoring the solution properties.