Ultra-high resolution sensing of glucose concentration based on amplified half-integer localized surface plasmons mode

Since the half-integer order localized surface plasmons mode is more sensitive to the change of the surrounding materials, an active spoof plasmonic microfluidic sensor using the mode for detecting minute change of glucose aqueous solutions has been proposed at microwave frequencies. By introducing an active coupling circuit near the slit of the spoof plasmonic resonator, the measured quality factor of the half integer order mode (n  =  1.5) for the active spoof plasmonic resonator is increased from 148 to 40 000 and the dephasing time is increased to about 16.5 µs when the optimal bias voltage is applied, compared to the passive spoof plasmonic resonator. The resonance frequency changes from 2.45 GHz to 1.74 GHz, with a frequency shift of 710 MHz, when the microfluidic channel is filled with distilled water (about 12 µl). The experiments show that the resonance frequency increases almost linearly with the concentration of the glucose solution. The limit of detection of the active sensor is 9 mg dl⁻¹. The figure of merit reaches 2236 MHz/(mg/dl). The high-resolution active spoof plasmonic sensor could find more potential applications for biological and chemical sensing. (paper)