Stretchable PEG-DA Hydrogel-Based Whispering-Gallery-Mode Microlaser with Humidity Responsiveness

Optical microcavities have been widely employed for sensing and detection, because of their ultrasensitive responsiveness to surrounding environment. Here we report an active disk-shaped whispering gallery mode (WGM) microcavity fabricated from a water-sensitive material of dye-doped PEG-DA hydrogel through two-photon polymerization. We demonstrate that as the environment humidity changes the microcavity can homogenously expand or shrink to keep the disk-shaped structure, producing stable WGM lasing emissions. We further show that the WGM wavelength of the microlaser shifts linearly as the humidity increases from 25% to 65%, resulting in a wavelength variation of about 1.72 nm, which indicates that the stretchable microlaser can be acted as a humidity sensor. Due to the "smart" response of humidity and biocompatibility of PEG-DA hydrogel material, our results provide a way to the design and fabrication of flexible PEG-DA hydrogel biochips for biomedical applications.