This paper presents an electromagnetically actuated platform for automated sample preparation and detection of nucleic acids. The proposed platform integrates nucleic acid extraction using silica-coated magnetic particles with real-time polymerase chain reaction (PCR) on a single cartridge. Extraction of genomic material was automated by manipulating magnetic particles in droplets using a series of planar coil electromagnets assisted by topographical features, enabling efficient fluidic processing over a variety of buffers and reagents. The functionality of the platform was demonstrated by performing nucleic acid extraction from whole blood, followed by real-time PCR detection of KRAS oncogene. Automated sample processing from whole blood to PCR-ready droplet was performed in 15 minutes. We took a modular approach of decoupling the modules of magnetic manipulation and optical detection from the device itself, enabling a low-complexity cartridge that operates in tandem with simple external instruments.

This paper presents a minimal dead-volume micro-connector fabricated using poly-dimethylsiloxane (PDMS) casting techniques for microfluidic applications. A simple and versatile method of fabricating a micro-connector to have an efficient interconnection to external large-scale fluid equipment was demonstrated. To eliminate the dead volume, a capillary was bridged to a micro-channel via a connection channel, which was formed by the removal of a metal wire after the PDMS casting process. The new method does not require any adhesive, precise drilling, delicate alignment procedure and micromachining processes. It could also effectively prevent blocking of the capillaries which was commonly observed while using adhesives. With this approach, detachable and reusable micro-connectors with a minimal dead volume could be achieved. According to leakage tests, the micro-connector could withstand pressures up to 150 psi and a maximum flow rate of 50 µl min −1 . The pull-out tests indicated that the PDMS fitting could provide enough mechanical strength for practical applications. Not only does this micro-connector significantly eliminate the dead volume, but it also increases the detection signal. While compared with more conventional Teflon tubing fitting, the micro-connector could reduce by at least 50% the dilution effect for sample loading analysis due to substantial elimination of the dead volume. Most importantly, this micro-connector has greater versatility for coupling capillaries to various kinds of microfluidic chips made of different materials.

This study reports new three-dimensional (3D) micromachined magnetic tweezers consisting of micro-electromagnets and a ring-trap structure, fabricated using MEMS (micro-electro-mechanical systems) technology, for manipulating a single 2 nm diameter DNA molecule. The new apparatus uses magnetic forces to exert over 20 pN with less heating, allowing the extension of the DNA molecule over its whole contour length to investigate its entropic and elastic regions. To improve the localized DNA immobilization efficiency, a novel ring-trapper structure was used to handle the vertical movement of magnetic beads which were adhered to the DNA molecules. One extremity of the DNA molecule, which was bound to the thiol-modified magnetic bead, could be immobilized covalently on a gold surface. The other extremity, which was bound to another unmodified magnetic bead, could be manipulated under a magnetic field generated by micro-electromagnets. The important elastic modulus of DNA has been explored to be 453 pN at a low ionic strength. This result reveals that DNA becomes more susceptible to elastic elongation at a low ionic strength due to electrostatic repulsion. The force-extension curve for DNA molecules is found to be consistent with theoretical models. In addition to a single DNA stretching, this study also successfully demonstrates the stretching of two parallel DNA molecules.

A micromachine-based DNA manipulation platform for stretching and rotation of a single DNA molecule is reported. The DNA molecule with a 2 nm diameter could be successfully manipulated using magnetic forces generated by arrayed microcoils fabricated by MEMS (micro-electro-mechanical systems) technology. Key platform technologies including localized DNA immobilization, microcoil fabrication and microfluidics, have been integrated to form the DNA magnetic tweezers. One end of a single DNA molecule is specifically bonded onto a magnetic bead and the other end onto a gold surface. It is then manipulated under a magnetic field generated by built-in hexagonally aligned microcoils. Design and simulation of the magnetic tweezers are carried out by using numerical software. A highly effective and strong binding method for the construction of two sticky ends of a DNA is developed, which is compatible with MEMS technologies. To quantify the magnitude of magnetic forces acting on the DNA, force calibration is performed and further verified by the worm-like chain (WLC) model. The measured DNA stretching forces are found to be in reasonable agreement with the theoretical values. We have successfully demonstrated the stretching and rotation of the tethered-bead DNA molecule linked to a gold pattern using the developed method. The spring constant of the DNA molecule is experimentally found to be about 10−8–10−7 N m−1. The development of the proposed method could be useful for investigation of DNA biophysical properties.

This study demonstrated the feasibility of utilizing electrokinesis in an electrodeless dielectrophoresis chip to separate and concentrate microparticles such as biosamples. Numerical simulations and experimental observations were facilitated to investigate the phenomena of electrokinetics, i.e., electroosmosis, dielectrophoresis, and electrothermosis. Moreover, the proposed operating mode can be used to simultaneously convey microparticles through a microfluidic device by using electroosmotic flow, eliminating the need for an additional micropump. These results not only revealed that the directions of fluids could be controlled with a forward/backward electroosmotic flow but also categorized the optimum separating parameters for various microparticle sizes (0.5, 1.0 and 2.0 μm). Separation of microparticles can be achieved by tuning driving frequencies at a specific electric potential (90 Vpp·cm−1). Certainly, the device can be designed as a single automated device that carries out multiple functions such as transportation, separation, and detection for the realization of the envisioned Lab-on-a-Chip idea.