Construction of microfluidic biochips with enhanced functionalities using 3D femtosecond laser direct writing

The extreme nonlinear interaction betweenfemtosecond laser pulses and large-band-gapmaterials has enabled three-dimensional (3D)microfabrication inside transparent materials. In thepast decade, this technique has been used forcreating a variety of functional components in glassmaterials, including microoptics, microfluidics,microelectronics, micromechanics, etc. Using thesebuilding blocks, femtosecond laser microfabricationalso allows for construction of highly integratedmicrodevices. Here, we provide an overview of ourlatest progress made along this direction, includingfocal spot engineering and nanofluidic fabrication.In particular, we show that 3D micro-/nano-fluidiccomponents with arbitrary geometries can bedirectly formed inside glass. This opens uppromising prospects for a broad spectrum ofapplications based on compact and complex 3Dmicrofluidic networks. Our work shows that thistechnique holds promise for fabricating 3D hybridmicro-systems, such as Lab-on-a-chip devices andMicro Total Analysis Systems in the future

Femtosecond laser nanostructuring in glass with sub-50nm feature sizes

We report on controllable production of nanostructures embedded in a porous glass substrate by femtosecond laser direct writing. We show that a hollow nano-void with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. Our finding enables direct construction of 3D nanofluidics inside glass.Comment: 15 pages, 4 figure

Cost-effective microfabrication of sub-micron-depth channels by femto-laser anti-stiction texturing

Micro Electro Mechanical Systems (MEMS) and microfluidic devices have found numerous applications in the industrial sector. However, they require a fast, cost-effective and reliable manufacturing process in order to compete with conventional methods. Particularly, at the sub-micron scale, the manufacturing of devices are limited by the dimensional complexity. A proper bonding and stiction prevention of these sub-micron channels are two of the main challenges faced during the fabrication process of low aspect ratio channels. Especially, in the case of using flexible materials such as polydimethylsiloxane (PDMS). This study presents a direct laser microfabrication method of sub-micron channels using an infrared (IR) ultrashort pulse (femtosecond), capable of manufacturing extremely low aspect ratio channels. These microchannels are manufactured and tested varying their depth from 0.5 µm to 2 µm and width of 15, 20, 25, and 30 µm. The roughness of each pattern was measured by an interferometric microscope. Additionally, the static contact angle of each depth was studied to evaluate the influence of femtosecond laser fabrication method on the wettability of the glass substrate. PDMS, which is a biocompatible polymer, was used to provide a watertight property to the sub-micron channels and also to assist the assembly of external microfluidic hose connections. A 750 nm depth watertight channel was built using this methodology and successfully used as a blood plasma separator (BPS). The device was able to achieve 100% pure plasma without stiction of the PDMS layer to the sub-micron channel within an adequate time. This method provides a novel manufacturing approach useful for various applications such as point-of-care devicesPeer ReviewedPostprint (author's final draft

On the Formation of Nanogratings in Commercial Oxide Glasses by Femtosecond Laser Direct Writing

Nanogratings (NGs) are self-assembled subwavelength and birefringent nanostructures created by femtosecond laser direct writing (FLDW) in glass, which are of high interest for photonics, sensing, five-dimensional (5D) optical data storage, or microfluidics applications. In this work, NG formation windows were investigated in nine commercial glasses and as a function of glass viscosity and chemical composition. The NG windows were studied in an energy—frequency laser parameter landscape and characterized by polarizing optical microscopy and scanning electron microscopy (SEM). Pure silica glass (Suprasil) exhibits the largest NG window, whereas alkali borosilicate glasses (7059 and BK7) present the smallest one. Moreover, the NG formation windows progressively reduced in the following order: ULE, GeO2, B33, AF32, and Eagle XG. The NG formation window in glasses was found to decrease with the increase of alkali and alkaline earth content and was correlated to the temperature dependence of the viscosity in these glasses. This work provides guidelines to the formation of NGs in commercial oxide glasses by FLDW

In-chip direct laser writing of a centimeter-scale acoustic micromixer

A centimeter-scale micromixer was fabricated by two-photon polymerization inside a closed microchannel using direct laser writing. The structure consists of a repeating pattern of 20  μm×20  μm×155  μm acrylate pillars and extends over 1.2 cm. Using external ultrasonic actuation, the micropillars locally induce streaming with flow speeds of 30  μm s −1 . The fabrication method allows for large flexibility and more complex design

Fabrication of micro-/nanofluidic models and their applications for enhanced oil recovery mechanism study

”Micro-/nanofluidic model, as a potential powerful tool, has been used for decades for investigating fluid flow at pore-scale in energy field. It is still increasingly imperative nowadays to use different micromodels to direct observe pore-level fluid flow and analyze mechanisms of different enhanced oil recovery methods. In this work, three main tasks including three dimensional micromodels (1D,2D,3D) are proposed to fabricate and use for investigating different mechanisms of different enhanced oil recovery methods. For 1D capillary tube micromodel, we fabricate and use it to investigate the dynamics of a trapped oil droplet under seismic vibration. Seismic stimulation is a promising technology aimed to mobilize the entrapped non-wetting fluids in the subsurface. The applications include enhanced oil recovery or CO2 sequestration. For 2D micromodel, we fabricate to mimic unconventional dual-porosity shale-like tight porous media and investigate the fluid flow behavior under such conditions. Unconventional oil reservoirs have become significant sources of petroleum production and have even better potential in the future. Many shale oil systems consist of nanoscale pores and micro-scale fractures that are significantly smaller than those from conventional reservoirs. Therefore, it is increasingly important to investigate fluid flow behaviors in nanoscale channels. For 3D micromodel, we packed and sintered glass beads into quartz tubes to mimic 3D porous media. Because of difficulties for direct visualization, almost all the micromodels available are two-dimensional models which cannot represent real interconnected pore network of a real reservoir porous media. Thus, we build fully transparent 3D models to direct visualize and investigate the in-situ emulsification mechanism for nanogel flooding”--Abstract, page iv

Nanoscale local modification of PMMA refractive index by tip-enhanced femtosecond pulsed laser irradiation

Investigation techniques based on tip-enhanced optical effects, capable to yield spatial resolutions down to nanometers level, have enabled a wide palette of important discoveries over the past twenty years. Recently, their underlying optical setups are beginning to emerge as useful tools to modify and manipulate matter with nanoscale spatial resolution. We try to contribute to these efforts by reporting a method that we found viable to modify the surface refractive index of polymethyl methacrylate (PMMA), an acrylic polymer material. The changes in the refractive index are accomplished by focusing a femtosecond pulsed near-infrared laser beam on the apex of a metalized nano-sized tip, traditionally used in scanning probe microscopy (SPM) applications. The adopted illumination strategy yields circular-shaped modifications of the refractive index occurring at the surface of the PMMA sample, exhibiting a lateral size <200 nm, under 790 nm illumination, representing a four-fold increase in precision compared to the current state-of-the-art. The light intensity enhancement effects taking place at the tip apex makes possible achieving refractive index changes at low laser pulse energies (<0.5 nJ), which represents two orders of magnitude advantage over the current state-of-the art. The presented nanoimprinting method is very flexible, as it can be used with different power levels and can potentially be operated with other materials. Besides enabling modifications of the refractive index with high lateral resolution, this method can pave the way towards other important applications such the fabrication of photonic crystal lattices or surface waveguides

Microfluidics and Nanofluidics: Science, Fabrication Technology (From Cleanrooms to 3D Printing) and Their Application to Chemical Analysis by Battery-Operated Microplasmas-On-Chips

The science and phenomena that become important when fluid-flow is confined in microfluidic channels are initially discussed. Then, technologies for channel fabrication (ranging from photolithography and chemical etching, to imprinting, and to 3D-printing) are reviewed. The reference list is extensive and (within each topic) it is arranged chronologically. Examples (with emphasis on those from the authors’ laboratory) are highlighted. Among them, they involve plasma miniaturization via microplasma formation inside micro-fluidic (and in some cases millifluidic) channels fabricated on 2D and 3D-chips. Questions addressed include: How small plasmas can be made? What defines their fundamental size-limit? How small analytical plasmas should be made? And what is their ignition voltage? The discussion then continues with the science, technology and applications of nanofluidics. The conclusions include predictions on potential future development of portable instruments employing either micro or nanofluidic channels. Such portable (or mobile) instruments are expected to be controlled by a smartphone; to have (some) energy autonomy; to employ Artificial Intelligence and Deep Learning, and to have wireless connectivity for their inclusion in the Internet-of-Things (IoT). In essence, those that can be used for chemical analysis in the field for “bringing part of the lab to the sample” types of applications