Integrated High-Voltage for Dielectrophoretic Sorting in Microfluidic Plastic Devices

 

The principle of DEP sorting involves creating a non-uniform electric field within a microchannel. Particles experience a force dependent on their size, shape, and dielectric properties relative to the medium. By carefully designing electrode geometries and applying specific AC voltages, particles of interest can be deflected into a collection channel, while others continue straight. The voltage requirements are significant. For aqueous media, which are conductive, high-frequency AC fields (from tens of kHz to tens of MHz) are used to avoid electrolysis and bubble formation. The peak-to-peak voltages can range from 10 V to over 100 V, depending on the electrode gap and the DEP force required.

 

Integrating a high-voltage source into a plastic microfluidic chip presents a radical departure from conventional electronics. The goal is to embed the voltage generation and switching directly onto or within the chip itself. This is achieved using a combination of advanced materials and fabrication techniques. One approach involves fabricating thin-film transistors (TFTs) or other high-voltage switches directly onto a glass or silicon substrate, which then forms the base of the microfluidic chip. This active-matrix DEP technology, analogous to an LCD display, allows for the creation of millions of individually addressable electrodes on the chip. The high-voltage supply for this matrix is still external, but the distribution and switching are on-chip.

 

A more integrated approach aims to embed the entire power conversion onto the chip. This requires the development of high-voltage-compatible materials within the microfabrication process. For instance, using electroplating or screen printing to create thick-film inductors and transformers, and depositing high-quality dielectric layers for capacitors. The active components (diodes, transistors) would be fabricated using thin-film silicon or emerging metal-oxide semiconductor technologies. This would result in a fully monolithic device: a plastic or glass chip with microfluidic channels on one side and a complete AC high-voltage generator on the other, powered by a low-voltage battery.

 

The design of such an integrated power source must address several challenges. The first is isolation. The high-voltage AC signal (e.g., 50 Vpp at 1 MHz) must be contained within the electrode region and not couple into the fluidic inlets or the detection optics. This requires careful layout, with guard rings and shielding layers integrated into the chip stack. The second is power efficiency. On-chip power sources are limited by the thermal budget of the plastic substrate. The DC-AC converter must have high efficiency ( > 90% ) to avoid overheating the chip. This favors resonant or switched-capacitor topologies.

 

The third challenge is programmability. A useful DEP sorter requires the ability to change the voltage amplitude, frequency, and waveform (sine, square, pulsed) to optimize sorting for different particle types. This demands an on-chip digital controller that can set the parameters of the high-voltage oscillator. The control interface could be as simple as a few digital lines from an external microcontroller, or fully wireless using an on-chip antenna for near-field communication.

 

The integration of the high-voltage source eliminates the need for external wiring and connectors, which are often a source of unreliability and noise. It drastically reduces the footprint and power consumption of the overall system, enabling truly portable, point-of-care devices. A patient sample could be inserted into a disposable chip, and the sorting protocol would be executed entirely on-chip, with the results read by an integrated optical or electrochemical sensor. This convergence of microfluidics and power electronics, enabled by the relentless scaling of high-voltage components, promises to democratize complex cell analysis, bringing it from the centralized laboratory to the bedside or the field.