Nano-aquarium with microfluidic structures for dynamic analysis of Cryptomonas and Phormidium fabricated by femtosecond laser direct writing of photostructurable glass

We demonstrate fabrication of microchips with microfluidic structures for dynamic analysis of living cells using a femtosecond (fs) laser. Fs laser direct writing followed by annealing and successive wet etching in dilute hydrofluoric (HF) acid solution resulted in formation of three dimensional (3D) hollow microstructures embedded in photostructurable glass. The embedded microchannel structure enabled us to analyze unique phenomenon of Cryptomonas, which suddenly swims very fast under certain condition. Vector analysis of the driving force for the rapid motion was also carried out by introducing nano-beads into the microchannel, in which Cryptomonas was encapsulated. We also fabricated a microchip for observation of Phormidium moving toward a seedling root, which accelerates growth of the seedling. Using the embedded microchannel in the microchip, observation of Phormidium assemblage to the seedling root was easily carried out. Such microchips with microfluidic structures, referred to as a nano-aquarium, realize the efficient and highly functional observation of living cells.     

Microfluidic laser embedded in glass by three-dimensional femtosecond laser microprocessing

Microfluidic dye lasers three-dimensionally embedded in glass have been fabricated for what is believed to be the first time by integrating micro-optical and microfluidic components by use of a femtosecond laser. By pumping the microfluidic laser, in which the microfluidic chamber was filled with the laser dye Rhodamine 6G dissolved in ethanol, with a frequency-doubled Nd:yttrium aluminum garnet laser, lasing action was confirmed by analysis of the emission spectra at different pump powers. In addition, by arranging two microfluidic chambers serially in the glass, we built a microfluidic twin laser that produces an array of two simultaneous laser emissions with one pump laser.     

Fabrication of integrated microchip for optical sensing by femtosecond laser direct writing of Foturan glass

By the one-continuous fabrication procedure of hollow microstructures using femtosecond (fs) laser direct writing followed by thermal treatment, successive chemical wet etching and additional annealing, three-dimensional integration of microoptics with microfluidics, i.e., a planoconvex microlens with a microfluidic chamber, in a single Foturan glass chip was achieved. Further integration of an optical waveguide was performed through internal refractive index modification by fs laser direct writing after the fabrication of the microlens and the microchamber. An “all-in-one” microchip that is highly effective for on-chip photonic biosensing can be manufactured by the present technique with easy assembly of each microcomponent and without any cumbersome processes for stacking and joining substrates. Experimental demonstration of photonic biosensing using the integrated microchip has revealed that fluorescence analysis and absorption measurement of liquid samples can be performed with efficiencies enhanced by factors of 8 and 3, respectively.     

Three-dimensional microfluidic channel with arbitrary length and configuration fabricated inside glass by femtosecond laser direct writing

We demonstrate, for the first time to the best of our knowledge, fabrication of three-dimensional microfluidic channels with arbitrary lengths and configurations inside glass by femtosecond laser direct writing. The main fabrication process includes two steps: (1) direct formation of hollow microchannels in a porous glass substrate immersed in water by femtosecond laser ablation and (2) postannealing of the glass substrate at ～1150°C by which the porous glass can be consolidated. We show that a square-wavelike channel with a total length of ～1.4 cm and a diameter of ～64 μm can be easily produced ～250 μm beneath the glass surface.     

A microfluidic chip integrated with a microoptical lens fabricated by femtosecond laser micromachining

We report on the integration of microlens and microfluidic channels in fused silica glass chip using femtosecond laser micromachining. The main process includes three procedures: (1) femtosecond laser scanning for forming a hemispherical surface and a Y-shaped channel in the fused silica glass; (2) chemical etching of the sample for removal of the modified areas; and (3) oxyhydrogen (OH) flame polish for smoothening the surface of the microlens. In addition, we demonstrate that the fabricated microlens exhibits good imaging performance with a 5× magnification, showing great potential in future lab-on-a-chip applications.     

Water-assisted femtosecond laser ablation for fabricating three-dimensional microfluidic chips

When the femtosecond laser focused in the water, the breakdown will be induced. The generated high-speed jet and shock wave can be used to etch silica glass for fabricating three-dimensional (3D) microfluidic chips. We present a simple and practical method to produce 3D multilayer microfluidic chips in silica glass. This method offers high design flexibility and fabricating feasibility. We also introduce a convenient cleaning method for diluting and ejecting the ablated debris from microchannel. Therefore, the femtosecond laser induced high-speed jet and shock wave can be used to fabricate complex microfluidic chips in silica glass. Experimental results show that the diameter of microchannel is uniform and the complexity of the microfluidic chip is under control. As a proof of principle, we demonstrate the feasibility of the fabricating process by using the water-assisted femtosecond laser ablation.     

Three‐dimensional femtosecond laser micromachining of photosensitive glass for biomicrochips

Internal modification of transparent materials such as glass can be carried out using multiphoton absorption induced by a femtosecond (fs) laser. The fs‐laser modification followed by thermal treatment and successive chemical wet etching in a hydrofluoric (HF) acid solution forms three‐dimensional (3D) hollow microstructures embedded in photosensitive glass. This technique is a powerful method for directly fabricating 3D microfluidic structures inside a photosensitive glass microchip. We used fabricated microchips, referred to as a nanoaquarium, for dynamic observations of living microorganisms. In addition, the present technique can also be used to form microoptical components such as micromirrors and microlenses inside the photosensitive glass, since the fabricated structures have optically flat surfaces. The integration of microfluidics and microoptical components in a single glass chip yields biophotonic microchips, in other words, optofluidics, which provide high sensitivity in absorption and fluorescence measurements of small volumes of liquid samples.     

Femtosecond laser microprocessing with three-dimensionally isotropic spatial resolution using crossed-beam irradiation

We describe the use of a crossed-beam irradiation system in three-dimensional femtosecond laser microprocessing to obtain three-dimensionally isotropic spatial resolution. In the crossed-beam geometry, two orthogonal objective lenses are arranged to share a common focal point. The synthesized focal spot produces an isotropic illumination volume. We demonstrate that microfluidic channels with substantially circular cross-sectional shapes can be directly fabricated inside glass by using the crossed-beam irradiation system.     

Generating optical vortex with computer-generated hologram fabricated inside glass by femtosecond laser pulses

We introduce a novel method to generate the optical vortex with computer-generated hologram (CGH) fabricated inside glass by femtosecond laser pulses. The CGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre- or post-treatment of the material. We also realized the restructured optical vortex beams of both the transmission and reflection pattern with high fidelity using a collimated He-Ne laser beam. The total diffractive efficiency of both the transmission and reflection pattern is about 4.79%.     

飞秒激光湿法刻蚀微纳制造

飞秒激光微加工作为一种新型微纳制造技术,在复杂三维构型制作方面具有其独特的优势,但激光加工效率问题严重制约了飞秒激光微加工技术走向实际工程应用,提出一种飞秒激光湿法刻蚀微纳制造方法,以提高飞秒激光微加工的效率为突破口,通过调控激光与物质相互作用获得材料的目标靶向改性,进而结合化学湿法刻蚀实现硬质材料上的高效和高精度三维微加工,采用这一方法制作出的微透镜尺寸为80 m,球冠高6.7 m,表面粗糙度小于10 nm。利用这种方法,实现了不同结构与特性的高质量微透镜阵列的超精密制备,在石英内部也实现了螺旋微通道的复杂三维结构,螺旋通道直径为20 m,长径比超过100。     

Dynamic and Reversible Accumulation of Plasmonic Core‐Satellite Nanostructures in a Light‐Induced Temperature Gradient for In Situ SERS Detection

A surface‐enhanced Raman spectroscopy (SERS) detection method that allows dynamic on‐demand generation of SERS substrates at locations of interest for in situ molecular sensing is demonstrated. Thermal convection and thermophoresis, which are both generated in a laser‐induced temperature gradient, are used to accumulate suspended plasmonic nanostructures to form 3D SERS substrate. Raman signals of melamine, which is used as a model analyte, increase to ≈117‐fold within 2 min of laser irradiation because of the accumulation. In addition, it is demonstrated that the accumulation of the nanostructures is reversible, and that reproducible SERS effects can be obtained during a repeated heating and cooling process. Because of the capability of on‐demand generation of a high density of SERS hot spots at different locations in solution, this particle manipulation and SERS detection method is applicable to monitor temporal and spatial variations of the concentrations of molecules. The complexity of the detection system remains the same when using this method since all the measurements are performed with a conventional Raman system and simple fluid channels. The required temperature gradient is generated by the laser used to excite Raman signals, and no nanofabricated substrates and complicated microfluidic or optical components are needed.     

Fabrication and characterization of a granular film consisting of size-selected silver nanoparticles: application to a SERS substrate

Uniform-sized silver nanoparticles with average diameter of 13.7 nm have been prepared in the gas-phase by combining a pulsed laser ablation method with a low pressure-differential mobility analyzer (LP-DMA). By depositing the silver nanoparticles onto a silicon substrate, a granular film consisting of size-selected silver nanoparticles has been fabricated and its morphology and electronic properties have been examined using transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. This granular silver film serves as a highly active substrate for surface-enhanced Raman scattering (SERS).     

3D integration of microcomponents in a single glass chip by femtosecond laser direct writing for biochemical analysis

3D integration of microcomponents in a single glass chip by femtosecond laser direct writing followed by post annealing and successive wet etching is described for application to biochemical analysis. Integration of microfluidics and microoptics realized some functional microdevices like a μ-fluidic dye laser and a biosensor. As one of practical applications, we demonstrate inspection of living microorganisms using the microchip with 3D microfluidic structures fabricated by the present technique.     

Fabrication of three-dimensional microfluidic channels in glass by femtosecond pulses

Fabrication of three-dimensional microfluidic channels in glasses by water-assisted ablation with femtosecond laser pulses was investigated. The experimental results showed that formation of the photoinduced microchannels by femtosecond pulses depended on the incident laser power and the scanning speed. For the same scanning speed, the shape of cross-section of channels changed from ellipse to circle with increasing the laser power. Under the optimum condition of laser processing, we fabricated two layers of microfluidic channels with diameter of about 8 μm inside glass. The distance between two layers of microchannels was about 20 μm.     

Glass‐embedded silver nanoparticle patterns by masked ion‐exchange process for surface‐enhanced Raman scattering

Glass‐embedded silver nanoparticle patterns were fabricated by masked silver–sodium ion‐exchange process followed by etching to reveal the particles for surface‐enhanced Raman scattering (SERS). The intensity of the enhanced Raman signal is comparable to that of the fluorescence, and the detection limit of 1 nM for Rhodamine 6G has been achieved. Raman images at different etching depths and corresponding morphological images are compared to find optimal SERS signal. Our results demonstrate that silver nanoparticle patterns embedded in glass can be used as SERS‐active substrates. Nanoparticles can be formed in a glass of high optical quality and have potential to be integrated with optical waveguides for a sensor chip. Copyright © 2010 John Wiley & Sons, Ltd.     

Fabrication of 3D microfluidic structures inside glass by femtosecond laser micromachining

Femtosecond lasers have opened up new avenues in materials processing due to their unique characteristics of ultrashort pulse widths and extremely high peak intensities. One of the most important features of femtosecond laser processing is that a femtosecond laser beam can induce strong absorption in even transparent materials due to nonlinear multiphoton absorption. This makes it possible to directly create three-dimensional (3D) microfluidic structures in glass that are of great use for fabrication of biochips. For fabrication of the 3D microfluidic structures, two technical approaches are being attempted. One of them employs femtosecond laser-induced internal modification of glass followed by wet chemical etching using an acid solution (Femtosecond laser-assisted wet chemical etching), while the other one performs femtosecond laser 3D ablation of the glass in distilled water (liquid-assisted femtosecond laser drilling). This paper provides a review on these two techniques for fabrication of 3D micro and nanofluidic structures in glass based on our development and experimental results.     

以PAA为模板制备SERS基底及对三聚氰胺的检测

采用热蒸镀的方法直接在多孔氧化铝(porous anodic alumina,PAA)模板上蒸镀几微米的银膜,然后在HCl溶液中溶解掉模板,得到表面具有纳米尺度规则结构的银膜作为表面增强拉曼散射(surface-en-hanced Raman spectra,SERS)基底,并在该基底上测量了吡啶溶液(0.01 mol.L-1)的增强拉曼光谱,发现平均增强因子大于105。与直接在载玻片上蒸镀的银膜相比,具有纳米尺度规则结构银膜的增强效果提高了30倍。改变激发光功率测量吡啶的拉曼光谱,和普通拉曼散射一样,增强拉曼光谱的峰值强度随激发光强度线性变化,并在该基底上测量了三聚氰胺的拉曼光谱,发现在1 mW的激发功率下对于三聚氰胺的检出限为2.5 mg.L-1。     

The effects of heat treatment on microfluidic devices fabricated in silica glass by femtosecond lasers

We fabricated complex microfluidic devices in silica glass by water-assisted femtosecond laser ablation and subsequent heat treatment.The experimental results show that after heat treatment,the diameter of the microchannels is significantly reduced and the internal surface roughness is improved.The diameters of the fabricated microchannels can be modulated by changing the annealing temperature and the annealing time.During annealing,the temperature affects the diameter and shape of the protrusions in microfluidic devices very strongly,and these changes are mainly caused by uniform expansion and the action of surface tension.     

Self-assembled volume vortex grating induced by femtosecond laser pulses in glass

We presented a microfabrication process for optical volume vortex grating inside glass by femtosecond laser pulses. The self-trapped filament of femtosecond laser pulses can induce hundreds μm-long region refractive-index changes in glass. We realized the restructured optical vortex beams using a collimated He–Ne laser beam. The maximum first-order diffraction efficiency was about 19.6%. The volume vortex grating structure fabricated in glass is polarization dependent.     

Hybrid femtosecond laser microfabrication to achieve true 3D glass/polymer composite biochips with multiscale features and high performance: the concept of ship‐in‐a‐bottle biochip

True three‐dimensionally (3D) integrated biochips are crucial for realizing high performance biochemical analysis and cell engineering, which remain ultimate challenges. In this paper, a new method termed hybrid femtosecond laser microfabrication which consists of successive subtractive (femtosecond laser‐assisted wet etching of glass) and additive (two‐photon polymerization of polymer) 3D microprocessing was proposed for realizing 3D “ship‐in‐a‐bottle” microchip. Such novel microchips were fabricated by integrating various 3D polymer micro/nanostructures into flexible 3D glass microfluidic channels. The high quality of microchips was ensured by quantitatively investigating the experimental processes containing “line‐to‐line” scanning mode, improved annealing temperature (645°C), increased prebaking time (18 h for 1mm‐length channel), optimal laser power (1.9 times larger than that on the surface) and longer developing time (6 times larger). The ship‐in‐a‐bottle biochips show high capabilities to provide simultaneous filtering and mixing with 87% efficiency in a shorter distance and on‐chip synthesis of ZnO microflower particles.