TABLE OF CONTENTS An ideal sensor is a device that will only detect a desired target analyte that is present within a given sample. Unfortunately, most samples usually contain many other analytes that may interfere with the sensor's ability to detect the target analyte. As a result it becomes necessary to design sensors which are as specific as possible for an analyte so that the sensor will discriminate against any interferents present. This is achieved using molecular recognition, where the sensor contains what is called a host molecule or chemoreceptor that will selectively bind the target analyte (which is quite often referred to as a guest). Once a suitable host-guest chemistry has been found, the host molecules need to be immobilized or incorporated in some way into the sensor. Finally, a means of signaling that the binding/recognition event has occurred has to be found (transduction).
One of the key requirements for molecular recognition is the existence of pre-organized groups within the host molecule that can selectively enclose or bind the guest ion (single atom) or molecule. Examples of this kind of host-guest recognition can be seen in everyday living processes. All living organisms use enzymes, which are proteins that contain "pockets" that are designed to recognize a specific analyte. This means that only one specific analyte is capable of entering into the enzyme pocket. Enzymes can be used in sensors (biosensors), but they are commonly unstable and may not be readily available.
