Chemistry: electrical and wave energy – Apparatus – Electrophoretic or electro-osmotic apparatus
Reexamination Certificate
2002-07-30
2004-03-23
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrophoretic or electro-osmotic apparatus
C204S601000, C422S105000, C436S180000
Reexamination Certificate
active
06709559
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to microfluidic systems and devices and methods for their use. More particularly, the present invention provides structures and methods which facilitate the introduction of fluids into devices having microfluidic channels.
Considerable work is now underway to develop “microfluidic” systems, particularly for performing chemical, clinical, and environmental analysis of chemical and biological specimens. The term microfluidic refers to a system or device having a network of chambers connected by channels, in which the channels have mesoscale dimensions, e.g., having at least one cross-sectional dimension in the range from about 0.1 &mgr;m to about 500 &mgr;m. Microfluidic substrates are often fabricated using photolithography, wet chemical etching, and other techniques similar to those employed in the semiconductor industry. The resulting devices can be used to perform a variety of sophisticated chemical and biological analytical techniques.
Microfluidic analytical systems have a number of advantages over conventional chemical or physical laboratory techniques. For example, microfluidic systems are particularly well adapted for analyzing small sample sizes, typically making use of samples on the order of nanoliters and even picoliters. The substrates may be produced at relatively low cost, and the channels can be arranged to perform numerous specific analytical operations, including mixing, dispensing, valving, reactions, detections, electrophoresis, and the like. The analytical capabilities of microfluidic systems are generally enhanced by increasing the number and complexity of network channels, reaction chambers, and the like.
Substantial advances have recently been made in the general areas of flow control and physical interactions between the samples and the supporting analytical structures. Flow control management may make use of a variety of mechanisms, including the patterned application of voltage, current, or electrical power to the substrate (for example, to induce and/or control electrokinetic flow or electrophoretic separations). Alternatively, fluid flows may be induced mechanically through the application of differential pressure, acoustic energy, or the like. Selective heating, cooling, exposure to light or other radiation, or other inputs may be provided at selected locations distributed about the substrate to promote the desired chemical and/or biological interactions. Similarly, measurements of light or other emissions, electrical/electrochemical signals, and pH may be taken from the substrate to provide analytical results. As work has progressed in each of these areas, the channel size has gradually decreased while the channel network has increased in complexity, significantly enhancing the overall capabilities of microfluidic systems.
Unfortunately, work in connection with the present invention has found that the structures and methods used to introduce samples and other fluids into microfluidic substrates can limit the capabilities of known microfluidic systems. Fluid introduction ports provide an interface between the surrounding world and the microfluidic channel network. The total number of samples and other fluids which can be processed on a microfluidic substrate is now limited by the size and/or the number of ports through which these fluids are introduced to the microfluidic system. Known structures and methods for introduction of fluids into microfluidic systems also generally result in the transfer of a much greater volume of fluid than is needed for microfluidic analysis.
Work in connection with the present invention has also identified unexpected failure modes associated with known methods for introducing fluids to microfluidic channels. These failure modes may result in less than desirable overall reliability for microfluidic systems. Finally, a need has been identified for some mechanism to accurately pre-position different fluids within a contiguous microfluidic network, so as to facilitate a variety of microfluidic analyses.
It would therefore be desirable to provide improved structures, systems, and methods which overcome or substantially mitigate at least some of the problems set forth above. In particular it would be desirable to provide microfluidic systems which facilitated the transfer of small volumes of fluids to an introduction port of a microfluidic substrate, and to increase the number of fluids which can be manipulated within the substrate without increasing the overall size of the substrate itself. It would be particularly desirable to provide microfluidic introduction ports which could accept multiple fluid samples, and which were less prone to failure than known introduction port structures. Finally, it would be advantageous to provide microfluidic channel networks which are adapted to controllably pre-position differing liquids within adjoining channels for analysis of samples using differing fluid media.
SUMMARY OF THE INVENTION
The present invention overcomes at least some of the deficiencies of known structures and methods for introducing fluids into microfluidic substrates. In some embodiments, fluid introduction can be facilitated through the use of a port which extends entirely through the substrate structure. Capillary forces can be used to retain the fluid within such a through-hole port, rather than relying on gravity to hold the fluid within a cup-like blind hole. A series of samples or other fluids may be introduced through a single through-hole port by sequentially blowing the fluid out of the port, and replacing the removed fluid with different fluid. Advantageously, an array of such through-hole ports can wick fluids from the surfaces of a corresponding array of pins, thereby avoiding the need for complex pipette systems. In another aspect, the present invention provides microfluidic substrates having channels which vary in cross-sectional dimension so that capillary action spreads a fluid only within a limited portion of the channel network. In yet another aspect, the introduction ports of the present invention may include a multiplicity of very small channels leading from the port to a larger microfluidic fluid channel. These small channels filter out particles or other contaminants which might other vise block the microfluidic channel.
In a first aspect, the present invention provides a microfluidic system comprising a substrate having an upper surface, a lower surface, and a microfluidic channel disposed between these surfaces. A wall of the substrate borders a port for receiving fluid. The port is in fluid communication with the channel, and the port is open at both the upper surface of the substrate, and at the lower surface of the substrate.
Generally, the port has a cross-sectional dimension which is sufficiently small so that capillary forces restrain the fluid within the port. The specific size of the port will depend in part on the properties of the material along its border. The capillary forces between the port and the fluid can also be used to transfer the fluid from the outer surface of a pin, rather than relying on a complex pipette system. The use of a through-hole port also facilitates the removal of the fluid from the port, as the fluid can be blown through the substrate with differential pressure, or simply displaced from the port with an alternate fluid. Optionally, the lower surface of the substrate may have a hydrophobic material to prevent the sample from spreading along the lower surface, while a hydrophilic rod or capillary tube may facilitate decanting of the fluid from the port.
In another aspect, the present invention provides a method for introducing a fluid into a microfluidic channel of a substrate. The method comprises transporting the fluid from outside the substrate to a port of the substrate through a first surface. The port extends through the substrate, and opens on a second surface of the substrate. The microfluidic channel of the substrate is in fluid communication with the port between the first and second
Chow Calvin Y. H.
Parce J. Wallace
Sundberg Steven A.
Caliper Technologies Corp.
Filler Andrew L.
Olsen Kaj K.
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