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Improved optical manufacturing technologies have stimulated the development of miniaturized bulk-measurement systems. The development of fiber-optic and planar-optical wave-guide technologies and the emergence of silicon micromachining technologies have further stimulated the development of microsensor systems. Broadly defined, optical transducer technologies can be divided into the following categories: • miniaturized versions of bulk optical systems • evanescent wave techniques • micro-optomechanical systems Current sensor approaches rely on assays, require multiple steps, and use multiple reagents, all of which are difficult in field applications and require trained personnel.

Cells-on-a-chip systems show promise as sensors of easily measured responses, such as beat rate (cardiac cells). Action potentials can be correlated with biologically anticipated responses to stimuli, such as pharmaceuticals and toxins. Issues to be overcome include cell-to-substrate adhesion, signal input/output interpretation, cell culture to cell culture consistency, cell culture chamber designs, increasing the variety of cell types, and keeping cultures alive and well in the field. Research is still at an early laboratory stage, and application of the technology to portable sensing devices is not likely in the near future.

One is competition, a technique in which proteins in a sample bind to a capture reagent, in the process bumping off a detectable molecule bound to the capture agent. Various techniques are then used to turn the detached molecule into an amplifiable signal. This technology is not common for protein chips. The second detection method is to capture the protein and then detect it with a direct or indirect label. , a fluorescent molecule chemically attached to the cysteine, an amino acid). One could, for example, label all of the proteins to make them fluorescent and then detect their binding by fluorescence at the surface.