High Resolution Glucose Sensor Based on Spoof LSPs Mode

Spoof localized surface plasmonics (LSPs) have emerged as promising candidates for high-resolution microwave sensing due to their strongly localized electromagnetic field characteristics. This study first investigates the sensing behavior and underlying mechanisms of the asymmetric mode (ASM) and symmetric mode (SM), which result from the mode splitting of a single spoof LSPs mode. Subsequently, a dual-mode injection-locked oscillator (ILO) is designed, where the spoof LSPs resonator serves as a narrowband frequency-selective element and is connected to gain-assisted circuits via coupling arms. By precisely tuning two phase shifters to appropriate values, both ASM and SM modes are simultaneously locked and their resonance intensities are significantly enhanced, with corresponding quality factors (Q) reaching 13,821.65 for ASM and 548.01 for SM. Furthermore, the sensor's performance is evaluated by varying the glucose concentration in a capillary tube. Both theoretical analysis and experimental results confirm that the ASM exhibits superior sensing performance compared to the SM. When the glucose concentration ranges from 40 to 150  mg/dL, the active ASM mode achieves a resolution as high as 5  mg/dL. These findings demonstrate that active microwave sensors based on the ASM of spoof LSPs hold significant potential for high-sensitivity biochemical sensing applications.