The Origin of Microfuidics

The microfluidics based devices have intellectual roots in at least two diverse fields: microelectronics and bioanalytical chemistry. The computer chip paradigm inspired chemists and engineers to apply some of these same technologies to generate networks of channels through which fluids can be moved.

Not coincidentally, commercial microfluidics has its origins in California's Silicon Valley. The advent of microprocessors in the early 1970s and the subsequent development of highly integrated microelectronic devices later in the decade paved the way for microfluidics. The application of microfluidics to the bioanalytical realm derives from work done in the late 1980's by Andreas Manz, then an analytical chemist at Ciba Geigy (now Novartis), who originated the TAS , an early lab-on-a-chip. Manz envisioned the application of photolithography and chemical etching techniques for micromachining a complete microanalytical system on a chip to integrate sample preparation, chemical derivatization, electrophoretic separation, and detection using only nanoliters or picoliters of the test analyte.

In the course of investigating the TAS concept, Manz and his co-workers discovered that the phenomenon of electro-osmosis could be used to control the injection, flow and mixing of solutions.

Manz and coworkers joined forces with Jed Harrison's group (University of Alberta, Canada) to demonstrate the practicality of such a device. Their studies showed that channels 10m deep by 30m wide etched in glass could be used for capillary electrophoresis, offering high-resolution separations in as little as 15 seconds.

More importantly, they showed that creating electric potential differences across chip elements permitted the manipulation of flow and mixing of fluids. The combination of exceptionally fast separation times and miniscule sample sizes demonstrated that such micro-systems were not simply elegant curiosities, but had practical advantages as well.

The integration of nucleic acid sample preparation, amplification, and hybridization, became another technological goal for the microfluidics community during the 1990s.

The first major commercial thrust toward micro-scale nucleic acid target amplification originated from work done by Allen Northrup and co-workers (Lawrence Livermore Laboratory).2 They demonstrated that PCR reactions could run up to ten times faster in their micro-scale device than by conventional means.

Kricka and Wilding (University of Pennsylvania School of Medicine) independently devised a thermocycler capable of amplifying DNA contained in less than five microliters of solution.

In 1994, J. Michael Ramsey and co-workers (U.S. Department of Energy's Oak Ridge National Laboratory) began publishing a series of papers that extended the findings of Manz and Harrison and provided the fledgling microfluidics enterprise with some of its key intellectual property. The Ramsey group described a prototypical microfluidic device consisting of two perpendicular etched channels in the form of a cross with four reservoirs, one at each channel terminus.

Knowing About Microfluidic Chips

Although microfluidics has been a buzz word within industrial applications over the past 20 years, few developments in the point of care diagnostic sector have been transferred from the research setting to a commercial product that can be manufactured in high volume. The benefits of microfluidics are numerous: ease of use, reduced sample volumes and reaction times, higher data quality and reliable parameter control. The intricacy of the microfluidic chips means that little is required of the detection instrument and the integral automation means the user does not need to engage in multi-step reactions requiring a high level of skill. The challenge lies with validating the complex processes that deliver reagents in order, accurately and reproducibly.

Alongside the technical issues associated with microfluidic platforms the diagnostics industry also has difficulty in identifying a low cost manufacturing technique for the micro patterning needed. This article will explore these challenges and offer potential solutions.

Whilst the paramount requirement is result accuracy, any device designed for point of care also needs to be small, cheap, mobile, robust and fast to be successful. Microfluidic techniques allow manufacturers to produce devices which are lower cost, smaller and potentially hand-held. At the same time, all of the profit of a microfluidic diagnostic kit sits with the consumable device, so manufacturers need to focus on keeping unit costs low while maintaining efficacy.

‘Microfluidics as a basic processing technology clearly works at the proof of principle level but that is where most of the work ends, usually in a publication. Engineering the device into a manufacturable product requires some consideration of substrate material, device functionalisation, packaging and performance testing. Currently the biggest opportunity and largest potential barrier to moving micro and nano technology into the commercial environment lies in innovative manufacturing’, comments key opinion leader on lab-on-a-chip and microfluidic technology Professor Steve Haswell, University of Hull.

For polymer devices, two leading technologies can be applied to enable cost-effective mass production: Injection Moulding (IM) and Polymer Laminate Technology (PLT).

IM carries many advantages in addition to its rapid manufacture: it is low cost with secure supply chains and a large palette of polymers available.

Mass production of microfluidic chips using IM is perceived to be problematic because it lacks the precision to reproduce micro features reliably due to effects of polymer creep or shrinkage in the final products.

Looking to the horizon of next generation microfluidic diagnostics, research has been focused on microfluidic devices being produced on paper. Analogous to lateral flow diagnostics, these microfluidic devices use hydrophobic channel walls printed on paper to allow the liquid flow direction and speed to be controlled. These paper based devices are extremely low cost and readily disposable. Although currently limited to relatively simple device architectures, this new platform approach is certainly one to watch for the future.