For the first time, proteins, a promising biocompatible and functionality-designable biomacromolecule material, acted as the host material to construct three-dimensional (3D) whispering-gallery-mode (WGM) microlasers by multiphoton femtosecond laser direct writing (FsLDW). Protein/Rhodamine B (RhB) composite biopolymer was used as optical gain medium innovatively. By adopting high-viscosity aqueous protein ink and optimized scanning mode, protein-based WGM microlasers were customized with exquisite true 3D geometry and smooth morphology. Comparable to previously reported artificial polymers, protein-based WGM microlasers here were endowed with valuable performances including steady operation in air and even in aqueous environments and a higher quality value (Q) of several thousands (without annealing). Due to the “smart” feature of protein hydrogel, lasing spectrum was responsively adjusted by step of ~0.4 nm blueshift per 0.83-mmol/L Na₂SO₄ concentration change (0 ~ 5-mmol/L in total leading to ~2.59-nm blueshift). Importantly, other performances including Q, FWHM, FSR, peak intensities, exhibited good stability during adjustments. So, these protein-based 3D WGM microlasers might have potential in applications like optical biosensing and tunable “smart” biolasers, useful in novel photonic biosystems and bioengineering.

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.