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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. [ABSTRACT FROM AUTHOR]

Herein, by using maskless and noncontact femtosecond laser direct writing (FsLDW) form protein aqueous ink, protein-based Y-junction optical micro/nano-splitters (PYOMs) have been readily customized with environmental-stimulus-actuated light-splitting adjustments for the first time to our knowledge. Bio/eco-compatible protein-based biopolymer successfully acted as the ideal alternative of artificial polymers for optical waveguide devices. Based on flexibly programmable “one-step” FsLDW, applicable shape-symmetric PYOMs were facilely fabricated with tailorable light-power-splitting ratios (from ∼1:1 to ∼3:1 in air). Significantly, via environmental responses and sensitivity of protein hydrogels, another type of “heterogeneous” PYOMs exhibited “smart” dynamic adjustments of light-power-splitting ratios by simply tuning surrounding chemical stimuli for example of pH value (∼1:1 in air, ∼1.35:1 in pure water, and 1.48:1–1.85:1 under pH 2.0–6.0), showing their application promise for optical sensing and environment-signal-actuated tunable micro/nano-optics. [ABSTRACT FROM AUTHOR]