In this letter, we demonstrate a two step casting process to fabricate a bifunctional hydrogel-based microlens array, which responds to both temperature (becomes opaque above certain temperature) and pH (changes its focal length at different pH levels), and can be operated in air for an extended period of time. Each lens in the array is 1 mm in diameter and its focal length changes from 4.5 to 55 mm when the environmental pH is varied between 2.0 and 5.0. The light-switching capability is measured to be ~92% when temperature increases from 25 to 35C.
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