A Minimally Invasive Implantable Sensor for Continuous Wireless Glucose Monitoring Based on a Passive Resonator

An implantable biosensor for the long-range continuous glucose monitoring is proposed in this letter. A fully passive, miniaturized circuit composed of an
LC
(inductor–capacitor) tank resonator with a volume of 16 mm
$^3$
is developed. This passive circuit can be implanted under the human skin, where the interstitial dermal fluid surrounds the
LC
tank resonator. Variations in glucose concentration result in variations in the permittivity of the fluid. In turn, this variation changes the capacitance of the
LC
tank resonator and, thus, its resonant frequency. The change in the resonant frequency is observed by the inductively coupled reader antenna located outside the tissue. Measurements are performed for various glucose concentrations in deionized water and human serum albumin, to check the validity of the proposed method in the presence of skin and fat phantom tissues. The results indicate a linear variation of the sensor's resonant frequency with respect to the glucose concentration within the range 0–500 mg/dL and a sensitivity of about 150 kHz/(mg/dL). Measurement results are reliable up to a distance of 10 mm between the reader and the sensor.