Plasmonic Metamaterial-Based Label-Free Microfluidic Microwave Sensor for Aqueous Biological Applications

This paper reports a label-free, highly sensitive plasmonic metamaterial inspired multi-band planar microwave sensor for aqueous biological samples. The proposed sensor consists of a spoof surface whispering gallery mode (SS-WGM) resonator connected to a spoof surface plasmons polariton (SSPP) transmission line in a special arrangement. The SS-WGM resonator of the proposed sensor is capable of localizing the electromagnetic (EM) field into a specific region due to its slow-wave propagation characteristics. This feature enhances the interaction time of the sample under test (SUT) with EM wave and offers higher sensitivity. The EM wave localization enables the proposed design to sense the small volume of the bio-samples. This is required in the case of the aqueous samples because a large volume of SUT absorbs radio frequency (RF) signals and reduces the ${Q}$ -factor of the sensors. The microfluidic approach has been adopted as it supports a small sample size. The proposed sensor is numerically analyzed and optimized for multi-band capability using full-wave EM simulation. To ensure maximum sensitivity, the microfluidic channel is kept appropriately above the hot-spot of the sensor. Glucose aqueous solution is being used here as a biological sample. Experimental validation of the proposed approach has been done using different concentrations of the SUT. The proposed sensor offers a maximum measured sensitivity of 77.3e−02 MHz/mgml−1, which shows a fair improvement in the sensitivity as compared to the state-of-the-art. It is anticipated that the proposed microfluidic planar microwave sensor is paving the path for the development of the microwave-based modern lab-on-chip system arrangement.