The manipulation of biological cells is essential to many biomedical applications. Insulator-based dielectrophoresis (iDEP) trapping consists of insulating structures which squeeze the electric field in a conductive solution to create a non-uniform electric field. The iDEP trapping microchip with the open-top microstructures was designed and fabricated in this work. For retaining the merit of microfabrication, the microelectrodes were deposited on the substrate to reduce the voltage required, due to the shortened spacing between them. The dielectrophoretic responses of both live and dead HeLa cells under different frequencies (100 Hz, 1 kHz and 1 MHz) have been investigated herein. The live cells exhibited negative dielectrophoresis at low frequencies of 100 Hz and 1 kHz, but a positive dielectrophoretic response with the frequency at 1 MHz. As for dead cells, positive dielectrophoretic responses were shown at all the frequencies applied. Therefore, selective trapping of dead HeLa cells from live cells was achieved experimentally at the frequency of 1 kHz. The open-top microstructures are suitable for trapping cells or biological samples, and easily proceeding to further treatment for cells, such as culturing or contact detection. The intensity of the emitted light during fluorescent detection will not suffer interference by a cover, as it does not exist herein.

The ability to manipulate biological cells is a fundamental need of many biological and medical applications. Insulator-based dielectrophoresis (iDEP) trapping involves the use of insulating structures that squeeze the electric field in a conductive solution to create a nonuniform electric field. In this work, a microchip was designed and fabricated for iDEP trapping with open-top microstructures. Microelectrodes were deposited on the substrate and the voltage required was minimized by reducing the distance between them. Human carcinoma (HeLa) cells were trapped under different frequencies to demonstrate the usability of the present microchip. Negative and positive dielectrophoresis (DEP) of cells were observed at low and high frequencies, respectively. The open-top microstructures are suitable for trapping cells and biological samples that can then easily undergo further treatment, such as culturing or contact detection. Since the cover is absent in open-top microstructures, there is no interference in the intensity of the emitted light during fluorescent detection. Furthermore, the Joule heat, which is generated by the application of high voltage in the open-top microstructure, can be dissipated more effectively.

Cell Trapping Utilizing Insulator-based Dielectrophoresis in The Open-Top Microchannels(1) II. DIELECTROPHORETIC(DEP) FORCE THEORYThe phenomenon ofDEP is first defined by Pohl (1978) as the motion of neutral particles caused by dielectric polarization effects in non-uniform electric fields that alternating fields of a wide range of frequencies were used. The DEP force F DEP acting on a spherical particle of radius r suspended in a fluid of permittivity Em is given:) application to automation because DEP traps consist of scalable electrode arrays be designed to pattern thousands of cells on a single glass slide. DEP have been using as cell trapping [13], levitation [14], separation [15], and sorting [16] on an electrode array by varying electrode shape and arrangement. DEP on micro-fabricated electrodes has been proved especially suitable for its relative ease of micro-scale generation and structuring of an electric field on microchips.DEP force field could also be generated by using dielectric constrictions or insulating obstacles, therefore, these methods further extend the scope of DEP applications. These approaches have been termed electrodeless dielectrophoresis (EDEP) [17] or insulator-based dielectrophoresis (iDEP) [18], respectively, in distinguishing from the method conventionally employed by metal electrodes-based DEP for force generation.In this study, a lower conductive material of photoresist (JSR, THB I5IN) was adopted as a structure in open-top microchannel instead ofa metallic wire to squeeze the electric field in a conducting solution, therefore, creating a high field gradient with a local maximum. The microchip with the open-top microchannels was designed and fabricated herein. The schematic illustration of the trapping device is shown in Fig 1. This trapping microchip is suitable for trapping cells or biological samples and easily proceeding further treatment for cells, such as culturing or contact detection. Biological sample and buffer loading before analysis and cleaning after analysis in the proposed microchip with the open-top microchannels could become easier and faster, hence, it is beneficial in high-speed sequential multiple measurements. Furthermore, the Joule heat generated by applying high voltage in the open-top microchannel could dissipate more effectively than that in the enclosed microchannel, because that it is open to the air. When the fluorescent detection is used, the intensity ofthe emitted light will not be interfered by the cover, which is absent in the microchip with open-top microchannels.