Plastic diagnostic lab-on-a-chip
A low-cost portable polymer tool that allows for quick diagnoses in remote environments is being developed by a group of researchers.
The Surface Enhanced Micro Optical Fluidic Systems (SEMOFS) project, sponsored by the European Sixth Framework Programme, is investigating cyclic olefin copolymer and polycarbonate labs-on-chips, which are cheaper than silicon or glass alternatives, making them ideal for disposable applications.
The chips are composed of a series of micrometre-sized channels through which a blood or serum sample is injected. Various antigens on the sensor surface bond to specific proteins in the sample. An integrated optical sensor detects any refractive index change that may be caused by the presence of the bound proteins.
Upon connection to a cartridge reader, the system provides a quick interpretation of the proteins found. Some, for example, can signal the early signs of cancer, explains Joerg Nestler of the Chemnitz University of Technology, in Germany, which is coordinating the project.
Slip and slide
One key element to the system is microfluidic transport of the sample and reagents through various channels. Hydrophilic and hydrophobic surfaces help control the fluid flow and reduce unwanted protein adsorption.
Oxygen-containing fluorocarbon polymer films are applied to the channels using plasma enhanced chemical vapour deposition. By increasing oxygen levels in the films, hydrophobic fluorocarbons within them are turned into hydrophilic materials. This allows for varying surfaces to be deposited, as required,by one machine, ‘although masking is necessary to deposit both materials side-by-side on one substrate’, says Jerome Gavillet of CEA Liten in Grenoble, France, who developed the channel surface modification process.
To help push the sample through a hydrophobic area, pressure is exerted from a hydrogen-oxygen gas mixture generated by a sodium polyacrylate-based hydrogel. Applying an electric voltage to the water in the hydrogel stored on the chip creates the gas. ‘We use the gel properties to allow for much simpler integration processes by stencil printing,’ explains Nestler.
For Tim Ryan, Managing Director of Epigem, a UK manufacturer of polymer-based microengineering products, this last innovation is the most novel aspect of the project. ‘I have not seen electrochemical generation of gas for pneumatic actuation before’, adding that this could be less energy demanding.
The aim of the project is to create a cheap and portable lab, notes Nestler. ‘This could be used in places where a central lab is too far away, such as in developing countries.’
However, Ryan says the chip may be expensive to make. ‘The cost of filling reservoirs and other assembly issues [can be high],’ he notes. ‘And the more complex the combination of technologies, the more concerns [there are] about yield and reliability.’
Nestler says the group has tried to keep the assembly process as simple as possible. It has created a working model of the microfluidics systems, though it is still working on the optical sensor aspect. When completed, the team aims to have a device that can be mass-manufactured using general techniques such as injection moulding, stencil or screen printing, or roll-to-roll adhesive tape structuring and assembly.
Further information: SEMOFS
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