Abstract
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.
Highlights
Environmental responsiveness[3,4], bio-illumination[8,10], tailorable soft mechanical characteristics[2,5,6,8], biocatalysis[14], and specific recognition[11,15]
Q > 2000 and full width at half maximum (FWHM) of ~0.25 nm were achieved in air even without annealing processing, better than similar WGM microlasers based on artificial polymers[27]
Even for protein-based 3D WGM microlasers operated in aqueous solutions, which was rarely reported previously using artificial polymers to our knowledge, Q was up to ~3300 and FWHM was as small as ~0.18 nm
Summary
Environmental responsiveness[3,4], bio-illumination[8,10], tailorable soft mechanical characteristics[2,5,6,8], biocatalysis[14], and specific recognition[11,15]. Facile and flexible functionalization is another significant advantage of biomacromolecule-based/-derived biomaterials via multi-methods like blending[11], chemical modification[16,17], and even gene-engineering customization[16,17] It offers a huge “module library” of natural functional biomaterials to select from as needed for applications in various fields, for example, bionics of structures and material-composition. The existing WGM optical microcavities and microlasers are built generally with silicon dioxide (SiO2)[18,19,20,21,22,23], semiconductors[24,25], artificial polymers[26,27], and synthetic organic crystals[28] These WGM-based optical microdevices are of great advantages including facile integration, high Q (related to photo-confinement in the cavities), and high detection sensitivity[29]. Along with increasing involvement in bio-related edge-cutting fields like label-free high-sensitivity detection[18,19,20,21,22] and optical micromanipulation[36], protein-based 3D WGM microlasers might open new opportunities for biological and medical applications such as optical biosensing, diagnosis, tunable “smart” biophotonics
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