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Fabrication of nanostructures with a feature size much smaller than the laser wavelength is challenging due to the optical diffraction limit. It’s well known that the irradiation of polarized ultrafast laser generates periodic nanostructures, so called laser-induced periodic surface structures (LIPSS). Owing to the modulated field, the surface is periodically ablated to form specific patterns, which can be used for some photonic applications including surface-enhanced Raman scattering (SERS). In this paper, we investigate the morphologies of LIPSS on ZnO substrates by mask-less ultrafast laser processing. By adjusting the laser processing parameters, including fluence, pulse number, polarization, and pulse duration, the homogenous nanostrip array and nanopillar array are created. Furthermore, by adjusting the laser fluence, a single nanogroove with a width of ∼20 nm and a single nanocavity with a diameter of ∼24 nm are created. The gold nanoparticles are then coated on the ZnO nanopillar array for SERS application. We found that the concentration of defects in ZnO substrate is increased by the laser irradiation, which is beneficial for SERS performances to achieve an enhancement factor of SERS as high as 2.28 × 107.

In the last decades, research and development of microfluidics have made extraordinary progress, since they have revolutionized the biological and chemical fields as a backbone of lab-on-a-chip systems. Further advancement pushes to miniaturize the architectures to nanoscale in terms of both the sizes and the fluid dynamics for some specific applications including investigation of biological sub-cellular aspects and chemical analysis with much improved detection limits. In particular, nano-scale channels offer new opportunities for tests at single cell or even molecular levels. Thus, nanofluidics, which is a microfluidic system involving channels with nanometer dimensions typically smaller than several hundred nm, has been proposed as an ideal platform for investigating fundamental molecular events at the cell-extracellular milieu interface, biological sensing, and more recently for studying cancer cell migration in a space much narrower than the cell size. In addition, nanofluidics can be used for sample manipulation in analytical chemistry, such as sample injections, separation, purifications or for quantitative and qualitative determinations. Among the nanofabrication technologies, ultrafast laser manufacturing is a promising tool for fabrication of nanofluidics due to its flexibility, versatility, high fabrication resolution and three dimensional (3D) fabrication capability. In this paper, we review the technological advancements of nanofluidic systems, with emphasis on fabrication methods, in particular ultrafast laser manufacturing. We present the challenges for issues concerning channel sizes and fluid dynamics, and introduce the applications in physics, biology, chemistry and engineering with future prospects.

The extremely high peak intensity associated with ultrashort pulse width of femtosecond laser allows us to induce nonlinear interaction such as multiphoton absorption and tunneling ionization with materials that are transparent to the laser wavelength. More importantly, focusing the femtosecond laser beam inside the transparent materials confines the nonlinear interaction only within the focal volume, enabling three-dimensional (3D) micro- and nanofabrication. This 3D capability offers three different schemes, which involve undeformative, subtractive, and additive processing. The undeformative processing preforms internal refractive index modification to construct optical microcomponents including optical waveguides. Subtractive processing can realize the direct fabrication of 3D microfluidics, micromechanics, microelectronics, and photonic microcomponents in glass. Additive processing represented by two-photon polymerization enables the fabrication of 3D polymer micro- and nanostructures for photonic and microfluidic devices. These different schemes can be integrated to realize more functional microdevices including lab-on-a-chip devices, which are miniaturized laboratories that can perform reaction, detection, analysis, separation, and synthesis of biochemical materials with high efficiency, high speed, high sensitivity, low reagent consumption, and low waste production. This review paper describes the principles and applications of femtosecond laser 3D micro- and nanofabrication for lab-on-a-chip applications. A hybrid technique that promises to enhance functionality of lab-on-a-chip devices is also introduced.