The future of biosensors

Since the development of the glucose sensor by Clark and Lyons in 1962, generally recognized as the first biosensor, many types of senso~ have been developed in which a physical or chemical transducer is provided with a layer containing a biological sensing elemenc The resulting device is called a biosensor, aimed to produce an electronic signal as a function of the concenuation of a chemical or biochemical constituent of a liquid, not necessarily of biological origin. Among the many proposed concepts, the integration of biologically active mae..':rials with a silicon chip is one of the most intriguing approaches, because it seems the most comprehensive integration between biology ~ electronics. In this paper the resulting biochips, mainly based on the field-effect principle as the coupling mechanism b~tween the two domains, will be described and discussed with an outlook on the future. Biosensors consist principally of two basic components, connected in series: a molecular recognition system and a physicochemical transducer, as schematically given in Fig. 1. The division into two parts is not limited to biosensors, because any chemical sensor can in fact be divided into a selector part and a transducer part, although they are not always recognized as such. For example, potentiometric electrodes make use of selective interracial chemical reactions between the electrode material and the liquid surroundings, leading to an inteffacial potential. The transducer part is in this case very simple: a thermodynamically well.defined electrical contact to make the inteffacial potential available for further handling. This action is usually called d~tection and the transducer is therefore also referred to as a detector, most often connected to an electronic amplifier. In the case of biosensors the word receptor is often used for the actual recognition part of the sensor, because in the natural chemical senses, such as olfaction, taste and neural biochemical pathways , the recognition phenomenon is performed by chemo-receptor cells. From a measurement point of view the interface between the receptor/selector and the transducer/detector part is very critical, because of the inherent sensitivity for interference from electrical fields in the case where the interface has a high electrical impedance. This becomes an even larger problem if relatively long leads are being used to connect the interface to a rumote amplifier ci" impedance converter. This measurement problem is one of the main reasons why in the field of chemical-sensor and bioscnsor research much attention is paid to the integration …