Three dimensional passivated-electrode insulator-based dielectrophoresis.

In this study, a 3D passivated-electrode, insulator-based dielectrophoresis microchip (3D πDEP) is presented. This technology combines the benefits of electrode-based DEP, insulator-based DEP, and three dimensional insulating features with the goal of improving trapping efficiency of biological species at low applied signals and fostering wide frequency range operation of the microfluidic device. The 3D πDEP chips were fabricated by making 3D structures in silicon using reactive ion etching. The reusable electrodes are deposited on second glass substrate and then aligned to the microfluidic channel to capacitively couple the electric signal through a 100 µm glass slide. The 3D insulating structures generate high electric field gradients, which ultimately increases the DEP force. To demonstrate the capabilities of 3D πDEP, Staphylococcus aureus was trapped from water samples under varied electrical environments. Trapping efficiencies of 100% were obtained at flow rates as high as 350 µl/h and 70% at flow rates as high as 750 µl/h. Additionally, for live bacteria samples, 100% trapping was demonstrated over a wide frequency range from 50 to 400 kHz with an amplitude applied signal of 200 Vpp. 20% trapping of bacteria was observed at applied voltages as low as 50 Vpp. We demonstrate selective trapping of live and dead bacteria at frequencies ranging from 30 to 60 kHz at 400 Vpp with over 90% of the live bacteria trapped while most of the dead bacteria escape.

3D Insulator-based dielectrophoresis using DC-biased, AC electric fields for selective bacterial trapping.

Insulator-based dielectrophoresis (iDEP) is a well-known technique that harnesses electric fields for separating, moving, and trapping biological particle samples. Recent work has shown that utilizing DC-biased AC electric fields can enhance the performance of iDEP devices. In this study, an iDEP device with 3D varying insulating structures analyzed in combination with DC biased AC fields is presented for the first time. Using our unique reactive ion etch lag, the mold for the 3D microfluidic chip is created with a photolithographic mask. The 3D iDEP devices, whose largest dimensions are 1 cm long, 0.18 cm wide, and 90 µm deep are then rapidly fabricated by curing a PDMS polymer in the glass mold. The 3D nature of the insulating microstructures allows for high trapping efficiency at potentials as low as 200 Vpp. In this work, separation of Escherichia coli from 1 µm beads and selective trapping of live Staphylococcus aureus cells from dead S. aureus cells is demonstrated. This is the first reported use of DC-biased AC fields to selectively trap bacteria in 3D iDEP microfluidic device and to efficiently separate particles where selectivity of DC iDEP is limited.

Embedded passivated-electrode insulator-based dielectrophoresis (EπDEP).

Here, we introduce a new technique called embedded passivated-electrode insulator-based dielectrophoresis (EπDEP) for preconcentration, separation, or enrichment of bioparticles, including living cells. This new method combines traditional electrode-based DEP and insulator-based DEP with the objective of enhancing the electric field strength and capture efficiency within the microfluidic channel while alleviating direct contact between the electrode and the fluid. The EπDEP chip contains embedded electrodes within the microfluidic channel covered by a thin passivation layer of only 4 µm. The channel was designed with two nonaligned vertical columns of insulated microposts (200 µm diameter, 50 µm spacing) located between the electrodes (600 µm wide, 600 µm horizontal spacing) to generate nonuniform electric field lines to concentrate cells while maintaining steady flow in the channel. The performance of the chip was demonstrated using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial pathogens in aqueous media. Trapping efficiencies of 100% were obtained for both pathogens at an applied AC voltage of 50 V peak-to-peak and flow rates as high as 10 µl/min.

Off-chip passivated-electrode, insulator-based dielectrophoresis (OπDEP).

In this study, we report the first off-chip passivated-electrode, insulator-based dielectrophoresis microchip (OπDEP). This technique combines the sensitivity of electrode-based dielectrophoresis (eDEP) with the high-throughput and inexpensive device characteristics of insulator-based dielectrophoresis (iDEP). The device is composed of a permanent, reusable set of electrodes and a disposable, polymer microfluidic chip with microposts embedded in the microchannel. The device operates by capacitively coupling the electric fields into the microchannel; thus, no physical connections are made between the electrodes and the microfluidic device. During operation, the polydimethylsiloxan (PDMS) microfluidic chip fits onto the electrode substrate as a disposable cartridge. OπDEP uses insulting structures within the channel as well as parallel electrodes to create DEP forces by the same working principle that iDEP devices use. The resulting devices create DEP forces which are larger by two orders of magnitude for the same applied voltage when compared to off-chip eDEP designs from literature, which rely on parallel electrodes alone to produce the DEP forces. The larger DEP forces allow the OπDEP device to operate at high flow rates exceeding 1 mL/h. In order to demonstrate this technology, Escherichia coli (E. coli), a known waterborne pathogen, was trapped from water samples. Trapping efficiencies of 100% were obtained at flow rates as high as 400 µL/h and 60% at flow rates as high as 1200 µL/h. Additionally, bacteria were selectively concentrated from a suspension of polystyrene beads.