In this context the term 'chip' is used loosely, unlike the 'traditional' silicon chip from electronics. LOC devices, or chips, can be fabricated from many types of material including various polymers (e.g. acrylic, polyester, and polycarbonate), glass, or silicon, as well as combinations of these materials. Unlike the 'traditional' silicon integrated circuit (IC) fabrication technologies, a broad variety of fabrication technologies are used for LOC device fabrication.
Almost all LOC systems have several common features including microfluidics and sensing capabilities. Microfluidics deals with fluid flow in small channels (e.g. sub-millimetre diameter) with flow control devices (e.g. channels, pumps, mixers and valves). Sensing capabilities including usually optical or electrochemical sensors are often integrated into the chip. Closely related fields to LOC systems are micro total analysis systems (μTAS), which focus primarily on the integration and miniaturization of analytical chemistry assays, and microelectromechanical systems (MEMS), which are the integration of mechanical and electrical elements (e.g. logical circuits, sensors, or actuators), can integrate decision-making capability with sensing and control elements on a chip. All of these technologies are based on the rapidly evolving field of microfabrication technology. LOC, μTAS and MEMS are overlapping technologies that often share the same elements (e.g. microfabrication, material, controls, and sensors).
It is a challenge to fully describe the fast-moving field of LOC in one publication. However, the two-volume work Lab-on-a-Chip Technology achieves this aim. It presents descriptions of some of the many types of LOC, including fabrication and application details, to give the reader a sense of the range of LOC technologies and the enormous potential that these devices possess.
A history of lab-on-a-chip technologyIn the early 1960s, several research groups started working on miniaturized silicon sensors. An early integrated LOC device was a complete gas chromatograph on a single 'chip' developed at Stanford University and published in 1979. This new tool was 'expected to find application in the areas of portable ambient air quality monitors, implanted biological experiments, and planetary probes'. The expectations for LOC have been realized repeatedly in the laboratory and commercial applications are beginning to be realized (Herold and Rasooly 2009. Lab-on-a-Chip Technology. Caister Academic Press ISBN: 978-1-904455-47-9).
In the 1980s and 1990s the LOC field moved rapidly and in the last decade approximately 3500 LOC related publications are indexed in Pubmed describing numerous fabrication methods and new applications using a broad array of technologies. The trend is towards more complex integrated multi-analyte LOC systems capable of more comprehensive analyses, utilizing advances in electronics and microfabrication that enable miniaturization and broader capabilities. The newest generation of LOC systems includes a miniaturized chip for isolation of rare circulating tumour cells in cancer patients and complex LOC devices utilizing valving technologies that provide dense fabrication and parallel pneumatic actuation of hundreds of valves.
- Lab-on-a-Chip Technology: Fabrication and Microfluidics
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