Huanfen Yao

A 3-

This paper presents a noninvasive wireless sensor platform for continuous health monitoring. The sensor system integrates a loop antenna, wireless sensor interface chip, and glucose sensor on a polymer substrate. The IC consists of power management, readout circuitry, wireless communication interface, LED driver, and energy storage capacitors in a 0.36-mm2 CMOS chip with no external components. The sensitivity of our glucose sensor is 0.18 μA·mm-2·mM-1. The system is wirelessly powered and achieves a measured glucose range of 0.05-1 mM with a sensitivity of 400 Hz/mM while consuming 3 μW from a regulated 1.2-V supply.

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We report the design, construction, and testing of a contact lens with an integrated amperometric glucose sensor, proposing the possibility of in situ human health monitoring simply by wearing a contact lens. The glucose sensor was constructed by creating microstructures on a polymer substrate, which was subsequently shaped into a contact lens. Titania sol-gel film was applied to immobilize glucose oxidase, and Nafion® was used to decrease several potential interferences (ascorbic acid, lactate, and urea) present in the tear film. The sensor exhibits a fast response (20s), a high sensitivity (240 μA cm(-2) mM(-1)) and a good reproducibility after testing a number of sensors. It shows good linearity for the typical range of glucose concentrations in the tear film (0.1-0.6 mM), and acceptable accuracy in the presence of interfering agents. The sensor can attain a minimum detection of less than 0.01 mM glucose.

CMOS Glucose Sensor for Wireless Contact-Lens Tear Glucose Monitoring

The increase in the diabetes population makes glucose monitoring a pressing demand for clinical and continuous use. Non-invasive sensing would allow a painless, convenient solution compared to traditional skin-piercing glucose meters. Among various body fluids, tear fluid, which is correlated to the glucose concentration in blood [1], is directly accessible on the eye and can provide a unique opportunity to develop an interface between a sensor and the human body. The current technique is to collect tear fluid samples in capillary tubes and assay the samples for glucose ex situusing standard laboratory instrumentation. Integrating sensors into a contact lens would provide a way to continuously and reliably sense metabolites in tear fluids.

A contact lens with embedded sensor for monitoring tear glucose level

We report a hydrogel-based contact lens with an encapsulated glucose sensor. The sensor is fabricated on a flexible transparent parylene film. The parylene-based sensor is then encased inside a soft contact lens made of poly(hydroxyethyl methacrylate) (polyHEMA) hydrogel. We test the glucose sensor with different concentrations of glucose and interfering chemicals found in tear film, such as ascorbic acid. The rapid response, good linearity and repeatability demonstrate the basic functionality of this soft contact lens.

A 3μW wirelessly powered CMOS glucose sensor for an active contact lens

We report a microscale dual (signal and control) glucose sensor on a contact lens, and test its performance using a physiologically accurate eye model built on a polymer platform complete with fluidic channels mimicking tear ducts. We show that the sensor incorporated into a contact lens has enough sensitivity to detect glucose at levels found in the tear film. We also demonstrate that the differential design can be used to reject the impact of interfering chemicals found in the tear film such as ascorbic acid, lactate and urea. The test platform presented here enables the testing of contact lenses in a controlled environment that mimics the surface of the eye.

A soft hydrogel contact lens with an encapsulated sensor for tear glucose monitoring

This work proposes a new time-domain integration method to realize Electrochemical Impedance Spectroscopy (EIS). Unlike traditional EIS systems which use a quadrature sinusoid stimulus, we propose a low-frequency, low-amplitude sinusoid stimulus, which is realized through a sinusoid DAC without the need for analog filter. The error caused by harmonic generation can be suppressed through integration in detection. The response current is sensed by a switched capacitor integrator with control synchronized with sinusoid DAC. The integration output is sampled and digitized by an 8-bit SAR ADC. The (1×1.1)mm2 prototype is fabricated in a 130nm CMOS process. It consumes 10μA from a 1.2V supply.

A dual microscale glucose sensor on a contact lens, tested in conditions mimicking the eye

Building an interface between a nano-scale system and the larger-scale world is of utmost importance in implementing and testing the system utility. By taking advantage of the enzyme function at the nano-scale, our group is developing functional contact lenses integrating electronic biosensors that can detect and report the level of glucose on the surface of the eye. In order to verify the functionality of the contact lenses we have developed a physiologically accurate mechanical model of a human eye which allows sensor characterization under thin-film conditions, in a controlled chemical environment. The polymer eye model replicates the geometry of an eye, the blinking motion of an eyelid, as well as the tear fluid input and output microchannels. Liquid used in the experiments was prepared to closely mimic the chemical and mechanical properties of biological tear fluid.