Glucose monitoring is a powerful weapon in the fight against diabetes, but the usual method of checking a patient’s blood sugar levels is through an enzyme-based finger-pricking method. A proposed alternative utilizes a fully integrated active contact lens system, providing wireless monitoring of glucose levels using the tear fluid in the eye.
The novel approach was proposed by Yu-Te Liao of the National Chung-Cheng University in Taiwan, along with Huanfen Yao, Andrew Lingley, Babak Parviz, and Brian Otis from the University of Washington (Seattle, WA). Their on-lens glucose sensor system detects the tear glucose level and then wirelessly transmits the information to an external reader. The goal for the on-lens sensor was a noise level of less than 1 nA root mean square (RMS) at a power consumption level of less than 5 µW, in a sensor area of approximately 0.36 mm2. The sensor IC consists of a power management block, readout circuitry, wireless communications interface, LED driver, and energy storage capacitors in the compact CMOS chip.
A loop antenna was designed with a 5-mm radius and 0.5-mm trace width. Assuming ideal antenna-chip matching, it could provide minimum gain of 1.76 dBi. Experiments were performed for use in the Industrial-Scientific-Medical (ISM) band at 1.8 GHz with good results on power consumption (about 3 µW consumed during operation). See “A 3-µW CMOS Glucose Sensor for Wireless Contact-Lens Tear Glucose Monitoring,” IEEE Journal of Solid-State Circuits, Vol. 47, No. 1, January 2012, p. 335.