Portland, Ore. -- While microfluidic devices that enable such popular applications as laboratories-on-a-chip are still mostly in the research stage, some companies are making strides toward commercial-grade applications.
Microfluidics enables chips to pipe fluids around their surfaces in micron-sized channels, either to perform a test hitherto only possible in a lab, or just to remove heat and cool a chip. The premiere application--labs-on-a-chip--enables battery-powered sensor-based devices to quickly detect trace amounts of almost any substance.
What are the blocks to volume production today? That depends on whom you ask, but three reasons loom large--a lack of chip-sized microfluidic pumps; a mismatch between micro-sized fluidic channels and the rest of a lab's equipment; and a lack of standards for interoperability among labs-on-a-chip from rival manufacturers.
Admittedly, a few companies are beginning to make commercial microfluidic devices, such as the integrated fluidic circuits (IFC) from Fluidigm Corp. (San Francisco). However, handheld labs-on-a-chip have so far only been realized by the U.S. Army, which has a lab-on-a-chip that enables soldiers to test for anthrax in the field.
Other companies like Caliper Life Sciences Inc. and Upchurch Scientific have actually cut back on their research efforts, said analyst Steven Bodovitz, a principal at BioPerspectives. "You need an application that cannot be done in any other way, to make it worth going to the trouble of using a lab-on-a-chip today," he said.
The first problem--a lack of chip-sized microfluidic pumps--was addressed recently by two new architectures for micropumps (see page 34). One from the University of Utah uses a "squeeze bottle" approach that houses the micropumps in a disposable polymer test card. The other from the Massachusetts Institute of Technology (Cambridge, Mass.) uses a novel photolithographic technique to gain electronic control over micropumping.
"The holy grail is an electrical function, where you apply a little current and all of a sudden fluids move," said professor Bruce Gale, the bioengineer at the University of Utah (Salt Lake City) who invented the "squeeze bottle" method of micropumping.
The second problem--mismatches between micron-scale labs-on-a-chip and the millimeter scale of most laboratory equipment--is being addressed by Cascade Microtech Inc. (Beaverton, Ore.). The company is the only maker of precision testers for microfluidic devices. Its research in microfluidic channel characterization, mostly for cooling chips, has just surpassed labs-on-a-chip. Fluid-cooled integrated circuits are at least five years away from widespread commercialization, however.
Cascade Microtech's L-Series introduced last year is the only available tester for engineers building microfluidic devices. The L-Series transfers the high-precision positioning possible with Cascade Microtech's wafer probes to its precision "microports" for fluidic input/output to chips. Each microport can deliver or receive fluid, electricity or both.
"Ours is the only development system available for characterizing chips with microfluidic channels--that is, without having to build fixtures or manifolds, and without having to permanently attach to the chips being characterized," said Cali Sartor, senior program manager for Cascade Microtech.
"Cascade Microtech's L-Series is greatly simplifying microfluidic development work today," said Bodovitz.
"Labs-on-a-chip are very elegant--they move fluids quickly in very, very small volumes. They are smaller, cheaper, faster, more accurate," said Bodovitz. "But the challenge is that it is difficult to get fluids onto and off of these chips--they are just so much smaller than the rest of the laboratory equipment available today."
Consequently, even if testing can be performed by a Cascade Microtech L-Series, manufacturing environments still require special fixtures to be built that adapt the millimeter-scale production equipment to the smaller micro scale of microfluidic devices.
"When the rest of the lab has been microminiaturized, and there are a wide variety of labs-on-a-chip available, that's when we will see much wider adoption of microfluidics than today," said Bodovitz.
The main advantage of microfluidic devices is that they can perform the same operations as a normal lab, but require only nanoliters of reagents and samples, thus speeding up reactions. The hope is that many of the tests that have to be performed in a lab overnight by skilled personnel, can someday be performed in minutes in the field by unskilled workers.
Sartor said the element holding back manufacturers from mass production is the inability to reliably reproduce results. Results achieved with one microfluidic device are not easily reproduced when the same operation is preformed by a microfluidic device from a different maker.
"What is preventing commercial adoption today, is unrepeatability," said Sartor. "Some chips are made out of brass, others are made from different kinds of plastic, and even if two devices are made from the same materials, there are specific properties regarding how the microchannels interact with the fluid--all of these need to be standardized in order for the test results from one lab-on-a-chip to match the results given by a lab-on-a-chip from a different manufacturer."
To that end, both the National Institute of Standards and Technology (NIST) and Semiconductor Equipment and Materials International (SEMI) have task forces working on interoperability standards. The goal of the NIST Microfluidics Metrology Task Force is to enable the widespread adoption of microfluidics.
"The NIST Fluidics Interface Task Force on interface standards is specifically targeting lab-on-a-chip with standards for materials and channels so that there can be repeatability among different manufacturers," said Sartor.
The SEMI MEMS Fluidics Interface Task Force, on the other hand, is working toward standardization of the fabrication of microchannels on semiconductor devices, the main use of which is for thermal cooling of integrated circuits.
"The SEMI Task Force is defining basic design criteria for microfluidic interconnections among chips, considering factors such as fluid type, pressure, flow rate, surface conditions, materials and their compatibilities," Sartor said.