Method and apparatus for controlling microfluidic flow

Abstract

An apparatus includes a pump; a gas pressure sensor; a microfluidic chip defining a microfluidic conduit; and a gas conduit providing fluid communication between the pump, the gas sensor and the microfluidic conduit; and a controller coupled to the pump and the gas pressure sensor, whereby the controller controls the pump, thereby controlling the gas pressure at the microfluidic conduit. An apparatus includes a microfluidic chip defining a microfluidic conduit extending from a microfluidic source electrode to a microfluidic ground electrode; a first resistor coupled to the microfluidic source electrode; a first and a second voltage divider, the first divider coupling a first power ground to a side of the first resistor opposite the microfluidic chip, the second divider coupling a second power ground to the lead between the first resistor and the microfluidic source electrode, and a first voltage sensor; and a second voltage sensor. Also included are methods of operating the apparatus.

Description

RELATED APPLICATION [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 656,237, filed on Feb. 25, 2005 the entire teachings of which are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] One goal of microfluidics is to provide precise, automated fluid processing on minimally sized samples. A key part of a microfluidic platform is the control instrumentation which manipulates the fluid samples in the microfluidic features (e.g., conduits and wells) of the microfluidic chip. Typically, fluid can be transported through the microfluidic features by an electrical or pressure gradient. [0003] Pressure-controlled fluid transport has been typically achieved with programmable syringe pumps, usually driven by stepper motors. Sample fluid can be loaded into a syringe pump and the output routed directly into a microfluidics chip. The syringe can be operated to create a pressure differential on the fluid, transporting it through the microfluidic c...

AI Technical Summary

Benefits of technology

[0023] The disclosed pressure control method and apparatus has several advantages. For example, in the disclosed pressure control method and apparatus, the pressures can be set by an analog control signal, allowing a number of pressure channels to be arranged in parallel. Also, the disclosed pressure control by nature can determine precise pressure at each channel, without the need for further equipment. The disclosed pressure control method and apparatus, being adaptable to analog control, can be adapted without any inherent pressure resolution limit by adjusting the feedback gain and choosing an appropriate gearing for the pump motor, in contrast to the inherent step size limit in syringe systems built with stepper motors. Thus, the resolution of the system is typically finer than the accuracy of the sensor, and thus pressure resolution typically is constrained only by the resolution and stability of the gas pressure sensor employed. Because the gas pressure sensor can be a macroscopic gas pressure sensor, many more options in price, range and precision can be available compared to special purpose miniature sensors. Also, it can be much easier to integrate off-chip pressure sensors, e.g., macroscopic gas pressure sensors into the disclosed pressure control than to embed a miniature gas pressure sensor in a microfluidics chip. Moreover, as shown in Example 1, pressure control can be achieved to better than the rated resolution of the pressure sensor. Further, the disclosed pressure control method and apparatus can also be employed with a passive channel for monitoring pressure. The disclosed pressure controller can be assembled from components that are generally simpler and cheaper than typical syringe pumps and their control systems. The disclosed pressure control method and apparatus can also be more compact and more easily networked than a comparable syringe pump system, especially for multi-channel systems.

[0024] The disclosed electrical control method and apparatus can provide closed loop control that can lead to more precise control in constant-current and constant-voltage modes, which can be chosen independently for each electrical channel. In either mode, continuous measurements of voltage and current can be made. Another feature is that the disclosed electrical control can be employed in combination with available programmable high voltage supplies, whereas previously such supplies were generally inadequate for microfluidics, for example because of the lack of precise current measurement capability.

Problems solved by technology

However, such programmable syringe pumps typically offer only open loop control without means to readily measure pressure differentials across the microfluidic features of the chip.

However, compared to the wide range of macroscopic pressure sensors available, such miniature pressure sensors can be expensive, limited in precision / range and difficult to integrate into microfluidic chips.

Moreover, syringe pump platforms can be difficult to adapt to multi-channel arrangements.

Also, operation and maintenance of a multiple syringe pump system can be labor intensive.

Moreover, dealing with several such high voltage electrical channels can present a challenge to measurement of an electrical channel's output current.

A conventional low-side current measurement can be impossible because a microfluidic chip typically has no common drain.

Also, non-contact “clamp” style current measurements typically would not be effective with direct currents in the microampere range.

Moreover, precise control of current and fluid transport can be difficult when employing high voltage supplies.

Although many basic regulated programmable high voltage power supplies are available, they are not typically useable in a microfluidics application without modifications or external measurement setups.

One reason for this is that many high voltage supplies are unable to sink current, which is generally not acceptable in a microfluidics chip where electrical channels can be directly interacting through the chip.

Another reason is that available high voltage supplies typically either have relatively coarse current monitoring or lack current monitoring altogether.

Commercially available electrical microfluidic controllers can be effective in some respects, but typically can be difficult or impossible to integrate with pressure control, which can be desirable for many experimental reasons (for example, for easily switching between fluids of widely different conductivities).

Moreover, many otherwise capable commercial controllers are not equipped to easily integrate with other typical lab instrumentation such as pressure controllers, heaters, spectroscopic detectors, microscopes, or the like.

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