A mm-sized implantable glucose sensor using a fluorescent hydrogel

This work proposes a millimeter-sized implantable glucose sensor using a fluorescent hydrogel based on boronic acids. The readout system is configured to provide an efficient wireless power transfer to the implantable sensor at 920-MHz frequency. The 675×959-µm² die fabricated in 180-nm CMOS consists of a rectifier, a bandgap reference, two regulators, a trans-impedance amplifier, two voltage-controlled ring oscillators, and a digital control with the total power consumption of 150 µW. The die is assembled with a 2.2 × 2.5-mm² antenna on PCB, an off-chip decoupling capacitor, an LED, and a photodiode. When the implantable sensor is surrounded by the fluorescent hydrogel and powered by the reader, the frequency of backscattered signals is encoded with the light intensity of the fluorescent glucose sensor, informing the glucose concentration. The miniaturization of the sensor minimizes the invasiveness, the potential discomfort, and immunity reaction against sensor, making it suitable for a long-term use after the implantation.