Making laboratory measurements on a chip

The routes of miniaturisation of chemical and biologicalmeasurements can be traced back to the developmentof a silicon chip based gas chromatograph by Terry, Jerman and Angell 1. This work was important becauseit was the first instance that techniques used in themicroelectronics industry were borrowed for the fabrication of a structure for chemical analysis. After a hiatus, Manz andco-workers2 in 1990 introduced the concept of micro total-analysissystems (µTAS); this has triggered an increasing interest in the de-velopment of nano and microsystems that can carry out operationsthat would normally be performed in the laboratory. More generally, systems that involve manipulation of liquids, typically in the pL tomL range, in channels that are typically in the micrometric range are referred to as Lab-on-a-chip or microfluidic devices3.

Traditionally chemical analysis has been performed by skilled personalusing large specialised equipment in central laboratories. There is now,however, an increasing interest in making the analysis on-site or in-situ.

For example, in environmental analysis, it would be preferable to makethe measurement in the river water rather than in a central laboratory and in clinical analysis we would prefer to be able to make the measurementby the patient’s bedside. There is now also a trend for measurements tobe carried out by non specialised people. Examples of this are pregnancy tests or blood glucose concentration tests for diabetic patients. For on site or in-situ measurements there is a need for the equipment to be smaller, easier to operate and reliable. The use of nano and microfabrication approaches allows us to create miniaturisedanalytical devices that are inherently smaller, have lower powerconsumption, give lower cost of analysis, are more reproducibleand can be produced in high volumes. The reduction in the cost of analysis will arise from a decreasing cost of the device but also because smaller volumes of reagents will be used. As the manufacturing approaches are further advanced then the complexity andfunctionality of the devices that can be created will be increased. This will allow increased automation, so that the devices can be used with minimal human intervention, as well as increasing the sophistication and number of operations that can be performed.