Two-step hybrid process of movable part inside glass substrate using ultrafast laser

We demonstrate a two-step hybrid process for fabricating movable parts inside glass substrate using the selective laser-induced etching (SLE) process that is consisted of laser-direct writing and wet chemical etching. To obtain an influence by the optical characteristics of a glass substrate when fabricating a 3D microstructure using the SLE, we analyzed the relationship of their dimensions between the designed and the fabricated devices. Two 3D microfluidic devices are designed and fabricated on glass substrates as the demonstrations of the hybrid process: a 3D microfluidic valve device with a movable plug and a 3D microfluidic mixer with a rotatable impeller and multilayer microchannels. The valving plug and the impeller of each device are successfully moved and rotated. The smallest structure is a pillar of the impeller device, and its size is 29 μm (diameter) × 277 μm (height). We expect this study to be extended to potential applications in 3D glass microfabrication and microfluidic systems.

Simple, Cost-Effective Fabrication, and Flow Dynamics Analysis of a Passive Microfluidic Mixer Using 3D Printing and Soft Lithography

Simple and low-cost fabrication of microfluidic devices has attracted considerable attention among researchers. The traditional soft lithography fabrication method requires expensive equipment like a UV exposure system and mask fabrication facility. In this work, an alternative and low-cost UV exposure system was introduced along with an alternative mask fabrication system. A previously reported passive microfluidic mixer was fabricated successfully using this modified soft lithography method. Challenges were presented during this modified fabrication method. Another emerging potential alternative for the fabrication of microfluidic mixers is 3D printing. It was also used in this experiment to fabricate a passive micromixer. This method is well known for rapid prototyping and the creations of complex structures. However, this method has several disadvantages like optical transparency, lower resolution fabrication, difficulties in flow characterization, etc. These problems were addressed, and the solutions were discussed in this work. Comparative analysis between 3D printing and soft lithography fabrication was presented. Flow characterization inside the 3D printed micromixer was carried out using the microparticulate image velocimetry (micro-PIV) system. It explains how the geometrical shape of the micromixer accelerates the natural diffusion process to mix the different fluid streams. Finally, a 3D numerical simulation of the passive micromixer was carried out to visualize the flow dynamics inside the micromixer. The flow pattern found from the numerical simulation and the experimental flow characterization is analogous. These observations could play an important role to design and fabricate cost-effective micromixers for lab-on-a-chip devices.

Rapid Microfluidic Mixing Method Based on Droplet Rotation Due to PDMS Deformation

Droplet-based micromixers have shown great prospects in chemical synthesis, pharmacology, biologics, and diagnostics. When compared with the active method, passive micromixer is widely used because it relies on the droplet movement in the microchannel without extra energy, which is more concise and easier to operate. Here we present a droplet rotation-based microfluidic mixer that allows rapid mixing within individual droplets efficiently. PDMS deformation is used to construct subsidence on the roof of the microchannel, which can deviate the trajectory of droplets. Thus, the droplet shows a rotation behavior due to the non-uniform distribution of the flow field, which can introduce turbulence and induce cross-flow enhancing 3D mixing inside the droplet, achieving rapid and homogenous fluid mixing. In order to evaluate the performance of the droplet rotation-based microfluidic mixer, droplets with highly viscous fluid (60% w/w PEGDA solution) were generated, half of which was seeded with fluorescent dye for imaging. Mixing efficiency was quantified using the mixing index (MI), which shows as high as 92% mixing index was achieved within 12 mm traveling. Here in this work, it has been demonstrated that the microfluidic mixing method based on the droplet rotation has shown the advantages of low-cost, easy to operate, and high mixing efficiency. It is expected to find wide applications in the field of pharmaceutics, chemical synthesis, and biologics.

Mixing Mechanism of Microfluidic Mixer with Staggered Virtual Electrode Based on Light-Actuated AC Electroosmosis

In this paper, we present a novel microfluidic mixer with staggered virtual electrode based on light-actuated AC electroosmosis (LACE). We solve the coupled system of the flow field described by Navier–Stokes equations, the described electric field by a Laplace equation, and the concentration field described by a convection–diffusion equation via a finite-element method (FEM). Moreover, we study the distribution of the flow, electric, and concentration fields in the microchannel, and reveal the generating mechanism of the rotating vortex on the cross-section of the microchannel and the mixing mechanism of the fluid sample. We also explore the influence of several key geometric parameters such as the length, width, and spacing of the virtual electrode, and the height of the microchannel on mixing performance; the relatively optimal mixer structure is thus obtained. The current micromixer provides a favorable fluid-mixing method based on an optical virtual electrode, and could promote the comprehensive integration of functions in modern microfluidic-analysis systems.

Development of Rapid and High-Precision Colorimetric Device for Organophosphorus Pesticide Detection Based on Microfluidic Mixer Chip

The excessive pesticide residues in cereals, fruit and vegetables is a big threat to human health, and it is necessary to develop a portable, low-cost and high-precision pesticide residue detection scheme to replace the large-scale laboratory testing equipment for rapid detection of pesticide residues. In this study, a colorimetric device for rapid detection of organophosphorus pesticide residues with high precision based on a microfluidic mixer chip was proposed. The microchannel structure with high mixing efficiency was determined by fluid dynamics simulation, while the corresponding microfluidic mixer chip was designed. The microfluidic mixer chip was prepared by a self-developed liquid crystal display (LCD) mask photo-curing machine. The influence of printing parameters on the accuracy of the prepared chip was investigated. The light source with the optimal wavelength of the device was determined by absorption spectrum measurement, and the relationship between the liquid reservoir depth and detection limit was studied by experiments. The correspondence between pesticide concentration and induced voltage was derived. The minimum detection concentration of the device could reach 0.045 mg·L−1 and the average detection time was reduced to 60 s. The results provide a theoretical and experimental basis for portable and high-precision detection of pesticide residues.