Advances in Biosensors for In Vitro Diagnostics

Biosensing Techniques And Examples

It is helpful to develop a framework to organize a discussion of biosensors. The basic schematic block diagram of a biosensor is shown in Figure 1. The sensing platform typically consists of a molecule—often termed a “biorecognition element”—which has a particular affinity for another biomolecule to be detected (Prasad, 2003). Of the four principal families of organic biomolecules which contribute to life (proteins, nucleic acids, saccharides and lipids), proteins and nucleic acids have received a great deal of attention as biorecognition elements, given their high specificity of intermolecular interactions. Binding of the recognition element to a target biomolecule is transformed into a measurable signal via a transduction process; this process may be facilitated by an external excitation or stimulus. As an example, consider a target biomolecule which is tagged with a fluorescent molecule and bound to a biorecognition probe molecule immobilized onto a biosensor. In this case, an ultraviolet excitation signal might be used to excite a fluorescence emission which is sensed using a photodetector and transduced into an electrical current. The current is then converted to a detected voltage, processed and used for further analysis or display.

Figure 1.

Conceptual framework for biosensor implementation

Biosensor implementations can be organized and classified using various schemas, based on the form of the biorecognition element, the physicochemical or electrical property which is converted into a measurable signal, or the type of external stimulus used to obtain that transduced signal. This is illustrated in Table 1, which describes a number of factors which may be involved in the implementation of a particular form of biosensor.