With the threat of a chemical or biological attack on the mainland heightened by the recent discovery of the chemical toxin ricin in North London, UK, the ability to detect the presence of such warfare agents has become paramount. Research being carried out at the Berkeley National Laboratory in California, USA, could pave the way for the development of a hand held device to analyse air, soil, or water samples for the presence of dangerous chemicals or biological toxins. Led by scientists Frantisek Svec and Jean Frechet the researchers have produced efficient microfluidic chips using novel monolithic polymer-based materials with the potential to detect biological and chemical weapons.
By combining two existing technologies - microfluidic chips and monolithic porous polymers - the Berkeley scientists have been able to substantially increase the amount of surface exposed to a sample, which in turn helps to extract a larger amount of substance.
Microfluidic chips are typically small rectangular plates of glass, silica, or plastic that feature narrow channels, which are used to isolate specific compounds from a sample. Most current microfluidic devices feature open channel architecture, so named because when a sample is injected for analysis into one of the narrow channels, the walls are the only part of the chip coated to extract the desired compound from the stream. The rest just flows through uncollected.
Increasing the Efficiency Using a Monolithic Polymer-Based Material
To increase the efficiency of current devices, Svec and Frechet filled the entire cross section of the channel with a monolithic polymer‑based material they invented together with Cong Yu and Thomas Rohr This not only greatly increased the surface-to-volume ratio, but also the channel’s loading capacity.
Preparation of the Monolithic Polymers
The porous monolithic polymers are prepared in situ by a UV initiated polymerisation process developed by the scientists, which is similar to the photolithographic patterning used in microelectronics. The chip’s channels are firstly filled with a liquid mixture of monomers and porogens. The mixture is then irradiated with ultraviolet light through a specifically designed mask. This triggers a polymerisation process that produces a solid but porous monolithic material, which completely fills the cross section of the channel. ‘The monolith itself is very easy to prepare in any lab,’ says Svec. ‘Since the number of potential applications and, therefore, the variety of shapes is rather broad, the monoliths must be prepared within the device in which they are used.’
How The Devices Works
A sample is then injected through this channel, and in a process called solid phase extraction, the porous polymer material absorbs the target compound while the remainder of the sample flows through. This absorbed material is later released using a solvent, allowing researchers to collect and analyse it. The technique can be used to prepare samples for DNA sequencing, protein mapping, enzyme, assays, chromatographic analysis, as well as evaluating the environment for pollutants.
Svec and his team are currently creating a toolbox of monolithic devices, such as mixers, preconcentrators, enzyme reactors, values and separate units. ‘These will eventually be combined within a microchip,’ he says. ‘This combination is not a trivial task since we must take into consideration a number of situations, such as the mutual compatibility of functions.’
Integrating the Technology into a Hand Held Device
The construction of a handheld device, however, will take a little longer to create. ‘The chip itself is certainly an important part of the hand held unit,’ says Svec. ‘The other parts include electronics, fluid distribution, programming and machining. The construction of the final device will require the combined efforts of numerous groups from very different areas.’ Although not a simple process, Svec believes that by working with several groups the instrument will be finished soon. This instrument would allow the analysis to be conducted onsite to determine the presence of a substance immediately.
One drawback to their current research is the inability to separate a compound from the polymer after it has been absorbed. However, in co‑operation with scientists from Sandia National Laboratory, the Berkeley Lab scientists are developing a more complex system called MicroChem. It will enable the collection of a compound using solid phase extraction, separation from the polymer using electrophoretic techniques, and, ultimately, the detection of specific compounds.