A contact lens with embedded sensor for monitoring tear glucose level

Abstract

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.

Published by Elsevier B.V.

Figures

Fig. 1

The sensor fabrication process and results: (a) a clean PET substrate is prepared; (b) the substrate is covered by photoresist and exposed to UV light through a mask; (c) the photoresist is developed; (d) thin metal films are evaporated on the sample; (e) after lift-off the metal pattern remains on the surface. After this step, the sensor is cut out of the polymer substrate and heat molded to the contact lens shape and functionalized with enzymes; (f) images of a sensor after it has been cut of the substrate ; (g) image of a completed sensor after molding held on a finger; (h) the sensor may be hardwired for testing.

Fig. 2

Images of the sensor as it goes through surface functionalization and the related measured responses. (a) sequential images of sensor pre-treatment with GOD/titania/Nafion®; (b) measured amperometric response for the sensor just incubated with GOD; (c) measured amperometric response for the sensor prepared with GOD/titania sol-gel film; (d) measured amperometric response for the sensor prepared with GOD/titania/Nafion®; (e) three controls (signals for buffer) for the same pretreatment of (b), (c), and (d); (f) the enlarged view of curve (b) and control of (b) for 120–360 sec.

Fig. 3

Measured amperometric response and calibration curve of the sensor: (a) current signals for successive addition of 0.1 mM glucose (G); (b) current signals for the same amount of buffer (no glucose); (c) calibration curve for glucose signals generated by averaging current values of 30–50 sec after each addition.

Fig. 4

Measured sensor repeatability and interference rejection. The results are based on typical amperometric measurements with three different sensors (n=3). The current signals here are generated by averaging current values of 30–50 sec after each addition. The interference solution ALU includes 50 µM ascorbic acid (A), 10 mM lactate (L) and 10 mM urea (U).

Fig. 5

Measured amperometric response for very low concentrations (0.01–0.07 mM) of glucose: (a) the amperometric response for successive addition of 0.01 mM glucose and addition of the same amount of buffer; (b) calibration currents based on three different sensors (n=3). The current signals here are generated by averaging current values of 30–50 sec after each addition.

Fig. 6

Measured amperometric response for glucose 0.1–0.6 mM for the same sensor: (a) right after preparation; (b) 2 days later; (c) 4 days later. The last step is the addition of the interference solution ALU, including 50 µM ascorbic acid (A), 10 mM lactate (L) and 10 mM urea (U).