Fabrication of Polymer Microfluidics: An Overview

Microfluidic platform technology has presented a new strategy to detect and analyze analytes and biological entities thanks to its reduced dimensions, which results in lower reagent consumption, fast reaction, multiplex, simplified procedure, and high portability. In addition, various forces, such as hydrodynamic force, electrokinetic force, and acoustic force, become available to manipulate particles to be focused and aligned, sorted, trapped, patterned, etc. To fabricate microfluidic chips, silicon was the first to be used as a substrate material because its processing is highly correlated to semiconductor fabrication techniques. Nevertheless, other materials, such as glass, polymers, ceramics, and metals, were also adopted during the emergence of microfluidics. Among numerous applications of microfluidics, where repeated short-time monitoring and one-time usage at an affordable price is required, polymer microfluidics has stood out to fulfill demand by making good use of its variety in material properties and processing techniques. In this paper, the primary fabrication techniques for polymer microfluidics were reviewed and classified into two categories, e.g., mold-based and non-mold-based approaches. For the mold-based approaches, micro-embossing, micro-injection molding, and casting were discussed. As for the non-mold-based approaches, CNC micromachining, laser micromachining, and 3D printing were discussed. This review provides researchers and the general audience with an overview of the fabrication techniques of polymer microfluidic devices, which could serve as a reference when one embarks on studies in this field and deals with polymer microfluidics.

Far Infrared-assisted Sample Extraction and Solvent Removal for Capillary Electrophoretic Determination of the Bioactive Constituents in Citri Reticulatae Pericarpium

Background:

Sample preparation is crucially important for the capillary electrophoretic measurement of the bioactive constituents in Citri Reticulatae Pericarpium because conventional solvent extraction is time-consuming and the solvent peaks seriously interfere with the measured capillary electropherograms.

Objective:

The objective of the present study is to establish far infrared-assisted sample preparation approaches for the analysis of Citri Reticulatae Pericarpium.

Methods:

Synephrine and hesperidin in Citri Reticulatae Pericarpium were determined by capillary electrophoresis in combination with far infrared-assisted sample extraction and solvent removal.

Results:

The effects of detection potentials, irradiation times and the voltages applied to the infrared generator were investigated to acquire the optimal assay conditions. Synephrine and hesperidin could be well separated within 6 min at a separation voltage of 9 kV in an alkaline borate solution. Satisfactory linearity was observed over the concentration range of 0.001 to 1 mM with the detection limits of 0.43 and 0.52 μM for synephrine and hesperidin, respectively. The results exhibited that far infrared irradiations could enhance the efficiencies of sample extraction and solvent removal during the sample preparation of Citri Reticulatae Pericarpium. The extraction time was significantly reduced to 6 min while the interference of the solvent peaks towards the electropherograms was eliminated.

Conclusion:

Far infrared-accelerated extraction and solvent removal were employed in the capillary electrophoretic determination of the bioactive constituents in Citri Reticulatae Pericarpium with satisfactory results. The ease, simplicity, efficiency and low cost of the novel sample preparation approaches indicate they may find a wide range of applications.

Far infrared-assisted removal of extraction solvent for capillary electrophoretic determination of the bioactive constituents in Plumula Nelumbinis

Far infrared radiation was employed in the rapid removal of the solvents in the extracts of Plumula Nelumbinis and standard mixture solutions to prevent the interference of the solvent peaks toward their capillary electrophoretic measurements. The sample solutions in small vials were exposed to far infrared ray at 60°C for 3 min to remove solvent. The dried samples in the vials were each dissolved into running buffer with the aid of ultrasonication for capillary electrophoresis analysis. The far infrared-assisted solvent removal approach was sucessfully applied in the rapid determination of neferine, liensinine, isoliensinine, rutin and hyperoside in Plumula Nelumbinis. The five analytes could be well separated within 12 min in a 40 cm long fused silica capillary at a separation voltage of 12 kV in a 50 mM borate buffer (pH 9.2). The results indicated that the interferences of the solvent peaks in the capillary electropherograms of the herbal drugs were eliminated completely.

Far infrared-assisted encapsulation of filter paper strips in poly(methyl methacrylate) for proteolysis

Filter paper strips were enclosed between two poly(methyl methacrylate) plates to fabricate paper-packed channel microchips under pressure in the presence of far infrared irradiation. After the enclosed paper strip was oxidized by periodate, trypsin was covalently immobilized in them to fabricate microfluidic proteolysis bioreactor. The feasibility and performance of the unique bioreactor were demonstrated by digesting BSA and lysozyme. The results were comparable to those of conventional in-solution proteolysis while the digestion time was significantly reduced to ∼18 s. The suitability of the microfluidic paper-based bioreactors to complex proteins was demonstrated by digesting human serum.

Ultrasonic bonding method for heterogeneous microstructures using self-balancing jig

Perfect sealing of heterogeneous microstructures in plastic-based microfluidic devices is a significant and urgent challenge to be able to apply them in various microfluidic-based applications, including biosensing, biofiltering, chemical reactors and lab-on-a-chip. In this study we report a simple but practical and effective method to bond a microstructure-incorporated microfluidic device using an ultrasonic bonding method. The specially designed hemisphere-shaped jig, which is called a self-balancing jig, provides a free motion in all x, y, and z directions. These unique properties of the jig allow us to precisely adjust and bond the heterogeneous microstructures in the device. A conventional jig shows in solution leakages around the heterogeneous microstructures while the self-balancing jig did not show any leakages in devices. Furthermore, the bonding performance was also confirmed by using a black ink and fluorescent dye solution. The micro-pillar arrays in the device also demonstrated its capability for selective filtering of microbeads. We believe that this technique would be a useful tool for producing microfluidic devices with heterogeneous microstructures.