Yun-Lu Sun

Dynamically tunable protein microlenses.

Proteins have been utilized in numerous photonic and optoelectronic devices, for example, in optical computation, organic light emitting diodes (OLEDs), waveguides, biomicro/nanolasers, organic field effect transistors (OFETs), and memory devices, because their unique optical, mechanical, electrical, and chemical properties are easily tailored to each application. The performance of as-prepared proteinbased photonic devices has been demonstrated to exceed that of devices that are made with currently available organic materials. The underlying motivation for the use of proteins in microdevices is not only abundance, inexpensiveness, and biodegradability, but also biocompatibility and the capacity to tune their properties through appropriate external stimuli. These features are highly desirable for biologically inspired microdevices, for example delicate miniaturized lenses that are similar to the “camera-type” eyes of human beings, the compound eyes of insects, the photosensitive microlens arrays of brittlestars, or the infrared-sensitive microlens receptor arrays of the fire beetle (Melanophila acuminata). Scientists have been highly motivated to fabricate these lens-like micro/nanostructures with the aim of producing small, multifunctional, artificial eyes by using dynamically adjustable and fully biocompatible proteins. However, the preparation of protein microlenses that have controlled geometry and precise positioning still poses a challenge. Herein, we report a promising approach for the production of biomimetic protein microlenses by facile and rapid maskless femtosecond laser direct writing (FsLDW). FsLDW is a well-known method for producing complicated 3D structures with nanometric resolution. Recently, pioneering work from Shear and co-workers demonstrated that protein hydrogel-based microstructures fabricated by FsLDWexhibit a unique responsiveness to chemical signals. This responsiveness could result in rapid and reversible changes in the size and shape of the structures after stimulation by environmental triggers. However, to our knowledge there are few reports on the development of practical and useful devices, such as a tunable microlens, that are made from this class of proteins. In this study, commercial bovine serum albumin (BSA, 300–500 mgmL 1 in aqueous solution) and a photosensitizer (methylene blue, MB, 0.6 mgmL ) were used to fabricate micro/nanoarchitectures. The cross-linking reaction is initiated through the excitation of photosensitive molecules to their triplet states. The photoexcited molecules then react directly with oxidizable moieties (type I process) or transfer the energy to ground state molecular oxygen (type II process) to form a reactive oxygen species, such as singlet oxygen (O2). In either case, excited-state intermediates catalyze the inter or intramolecular covalent cross-linking of oxidizable protein residues (see Scheme S1 in the Supporting Information). In other words, proteins with photooxidizable groups, such as Tyr, Trp, His, Met, and Cys, can absorb infrared or UV light to form reactive or ionized species that are capable of cross-linking with other oxidizable moieties. This mechanism appears to play a role in the formation of some types of cataracts and in the aging of skin. BSA and other proteins with oxidizable side chains “inherit” this photo-cross-linking ability, and can thus be used for multiphoton fabrication (Figure 1). Proof-of-concept protein microlenses were fabricated by using a FsLDW system of our own construction (Figure 1). The system was composed of a femtosecond titanium/ sapphire laser (Spectra Physics 3960-X1BB), a piezo stage with a precision of 1 nm (Physik Instrumente P-622.ZCD), and a set of two galvano mirrors. The 3D shapes of the microstructures were designed by using 3Ds Max and then the designs were converted into computer processing programs. Prior to the photo-cross-linking of the proteins at the focal spot, the beam from the femtosecond laser (80 MHz repetition rate, 120 fs pulse width, 780 nm central wavelength) was tightly focused by a high-numerical-aperture (NA= 1.35) oilimmersion objective lens (60 ). The horizontal and vertical scanning movements of the focused laser spot were achieved simultaneously by the two-galvano-mirror set and the piezo stage. After cross-linking, the sample was rinsed in water several times to remove unreacted proteins. Then the asformed protein microstructures were left on the chip. Surface topography (shape and roughness) plays an important role in the optical properties of protein microoptics. However, the surface roughness of BSA microstruc[*] Y. L. Sun, Prof. Dr. W. F. Dong, R. Z. Yang, X. Meng, L. Zhang, Prof. Dr. Q. D. Chen, Prof. Dr. H. B. Sun State Key Laboratory on Integrated Optoelectronics College of Electronic Science and Engineering Jilin University, 2699 Qianjin Street Changchun 130012 (China) E-mail: dongwf@jlu.edu.cn hbsun@jlu.edu.cn

Aqueous multiphoton lithography with multifunctional silk-centred bio-resists.

Silk and silk fibroin, the biomaterial from nature, nowadays are being widely utilized in many cutting-edge micro/nanodevices/systems via advanced micro/nanofabrication techniques. Herein, for the first time to our knowledge, we report aqueous multiphoton lithography of diversiform-regenerated-silk-fibroin-centric inks using noncontact and maskless femtosecond laser direct writing (FsLDW). Initially, silk fibroin was FsLDW-crosslinked into arbitrary two/three-dimensional micro/nanostructures with good elastic properties merely using proper photosensitizers. More interestingly, silk/metal composite micro/nanodevices with multidimension-controllable metal content can be FsLDW-customized through laser-induced simultaneous fibroin oxidation/crosslinking and metal photoreduction using the simplest silk/Ag+ or silk/[AuCl4]− aqueous resists. Noticeably, during FsLDW, fibroin functions as biological reductant and matrix, while metal ions act as the oxidant. A FsLDW-fabricated prototyping silk/Ag microelectrode exhibited 104-Ω−1 m−1-scale adjustable electric conductivity. This work not only provides a powerful development to silk micro/nanoprocessing techniques but also creates a novel way to fabricate multifunctional metal/biomacromolecule complex micro/nanodevices for applications such as micro/nanoscale mechanical and electrical bioengineering and biosystems.

High-performance magnetic antimicrobial Janus nanorods decorated with Ag nanoparticles

Silver nanoparticle-decorated magnetic-silica Janus nanorods, synthesized by an environmentally friendly in situ approach, show superior magnetic sensitivity, strong affinity binding to bacteria, and highly effective and long-term antimicrobial activity against bacteria. Such antibacterial nanomaterials could have great potential in biomedical applications due to their excellent biocompatibility and non-hemolytic property.

Magnetic colloidosomes fabricated by Fe3O4–SiO2 hetero-nanorods

Magnetic colloidosomes were fabricated by directing self-assembly of magnetic-mesoporous hetero-nanorods at the interface of water-in-oil droplets. Emulsions stabilized by the adsorbed particles without any surfactant indicate that such rod-like nanoparticles have specific advantages in making stable and intact shells than spherical particles. The integrity and emulsion stability of the colloidosomes were strongly influenced by the geometric shape of the hetero-nanorods. The optimum length of the nanorods to construct the colloidosomes was studied and demonstrated. The as-formed magnetic colloidosomes can exhibit unique encapsulation behaviors and show strong magnetic response properties, which will find huge potential application in multicompartment reactor, drug delivery and other biomedical fields.

Nanoporous TiO2/polyion thin-film-coated long-period grating sensors for the direct measurement of low-molecular-weight analytes.

We present novel nanoporous TiO(2)/polyion thin-film-coated long-period fiber grating (LPFG) sensors for the direct measurement of low-molecular-weight chemicals by monitoring the resonance wavelength shift. The hybrid overlay films are prepared by a simple layer-by-layer deposition approach, which is mainly based on the electrostatic interaction of TiO(2) nanoparticles and polyions. By the alternate immersion of LPFG into dispersions of TiO(2) nanoparticles and polyions, respectively, the so-formed TiO(2)/polyion thin film exhibits a unique nanoporous internal structure and has a relative higher refractive index than LPFG cladding. In particular, the porosity of the thin film reduces the diffusion coefficient and enhances the permeability retention of low-molecular-weight analytes within the porous film. The increases in the refractive index of the LPFG overlay results in a distinguished modulation of the resonance wavelength. Therefore, the detection sensitivity of LPFG sensors has been greatly improved, according to theoretical simulation. After the structure of the TiO(2)/polyion thin film was optimized, glucose solutions as an example with a low concentration of 10(-7) M was easily detected and monitored at room temperature.

Protein - Based Three-Dimensional Whispering-Gallery-Mode Micro-Lasers with Stimulus-Responsiveness

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.

Customization of Protein Single Nanowires for Optical Biosensing

An all-protein single-nanowire optical biosensor is constructed by a facile and general femtosecond laser direct writing approach with nanoscale structural customization. As-formed protein single nanowires show excellent optical properties (fine waveguiding performance and bio-applicable transmission windows), and are utilized as evanescent optical nanobiosensors for label-free biotin detection.

Sapphire-Based Fresnel Zone Plate Fabricated by Femtosecond Laser Direct Writing and Wet Etching

Here, we report a sapphire-based Fresnel zone plate (FZP), which is fabricated by femtosecond laser direct writing assisted with subsequent wet etching. With this method, we solved the problem of high surface roughness caused by ultrafast femtosecond laser processing. We have obtained ~12-nm average surface roughness smaller than 1/25 of the optical working wavelength. As-formed sapphire FZP also exhibited a well-defined geometry. More importantly, ultraviolet (UV) light focusing and imaging can be easily achieved. Due to the high material hardness, thermal and chemical stabilities of sapphire, such sapphire FZP, may have great potential in UV imaging and focusing under some harsh environments.

Fabrication of an anti-reflective microstructure on sapphire by femtosecond laser direct writing

Herein, we report a facile approach for the maskless production of subwavelength-structured antireflective surfaces on sapphire with high and broadband transmittance in the mid-IR: femtosecond laser direct writing assist with wet etching. With this method, inverted pyramid and cone arrays with a pitch of about 2 μm and a total height of near 900 nm on the sapphire were produced. The resulting subwavelength structures greatly suppress specular reflection at normal incidence. The transmission measurements between 3 and 5 μm are in agreement with the simulations performed using VirtualLab, and the transmittance reached a maximum value of 92.5% at 4 μm. The sapphire with subwavelength structures also exhibits angle-independent transmittance characteristics up to a high θ=60°. Therefore, these subwavelength structures on sapphire are of great technological importance in mid-IR optics, especially for the harsh-condition-applicable windows of military mid-IR devices.

Integrated optofluidic-microfluidic twin channels: toward diverse application of lab-on-a-chip systems

Optofluidics, which integrates microfluidics and micro-optical components, is crucial for optical sensing, fluorescence analysis, and cell detection. However, the realization of an integrated system from optofluidic manipulation and a microfluidic channel is often hampered by the lack of a universal substrate for achieving monolithic integration. In this study, we report on an integrated optofluidic-microfluidic twin channels chip fabricated by one-time exposure photolithography, in which the twin microchannels on both surfaces of the substrate were exactly aligned in the vertical direction. The twin microchannels can be controlled independently, meaning that fluids could flow through both microchannels simultaneously without interfering with each other. As representative examples, a tunable hydrogel microlens was integrated into the optofluidic channel by femtosecond laser direct writing, which responds to the salt solution concentration and could be used to detect the microstructure at different depths. The integration of such optofluidic and microfluidic channels provides an opportunity to apply optofluidic detection practically and may lead to great promise for the integration and miniaturization of Lab-on-a-Chip systems.