Detection systems electrochemical type

Requirements with respect to the label used to mark one of the immunoreagents are comparable to those in other postcolumn reaction detection systems [4]. The label should preferably allow sensitive and rapid detection and be nontoxic, stable, and commercially available. So far, mainly fluorescence labels have been employed (e.g., fluorescein), although, in principle, also liposomes, time-resolved fluorescence, and electrochemical or enzymatic labels are feasible. On the other hand, labels providing a slow response, including radioactive isotopes and glow-type chemiluminescence, are less suitable for immunodetection. 

Several implanted biosensors have been developed and evaluated in both animals and humans (see Chapter 4). Detection systems are based on enzymes, electrodes, or fluorescence. The most widely studied method is an electrochemical sensor that uses glucose oxidase. This sensor can be implanted intravenously or subcutaneously. Intravenous implantation in dogs for up to 3 months has demonstrated the feasibility of this approach. Alternatives to enzymes are being developed, including artificial glucose receptors. Less success has been achieved with subcutaneous implants. Implantation of a needle type of sensor into the subcutaneous tissue induces a host of inflammatory responses that alters the sensitivity of the device. Microdialysis with hoUow fibers or ultrafiltration with biologically inert material can decrease this problem. 

Spectroelectrochemistry [99] Is a hybrid technique resulting from the association of electrochemistry with spectroscopy via the use of cells with optically transparent electrodes [100-103]. The potential of this technique lies in the possibility of Identifying both the type and the amount of the species generated In an electrochemical step. The Intrinsic characteristics of spectroelectrochemistry require the use of fast measuring systems —spectroscopic image detectors in most cases [104-107]— and the consequent acquisition of the large number of data provided by the detection system In a short time by means of an oscilloscope or, even better, of a computer also allowing the subsequent exhaustive treatment of the raw data. 

Microfluidic devices that use electrical fields for fluidic propulsion perform successfully for a variety of electrically driven separations, and thus, present unique opportunities to the analytical and biomedical community. The availability of a broad range of microfluidic functional elements, materials, and processes facilitated the miniaturization of most types of electrically driven separations that use optical and electrochemical detection systems capillary electrochromatography... 

The improved commercial availability of solid-phase reaction systems, immobilized enzyme reactors and photochemical derivatization instruments is one such direction for a brief outline of some of these see [34]. There will undoubtedly be new developments in the application of analytical methods, particularly in liquid chromatography, that will exploit the practical advantages of these devices when they are linked to the most sensitive detection modes, particularly the fluorescence and electrochemical types of detector. 

Through the choice of stationary phase and eluent composition, the selectivity can be modulated, but the eluent must meet the requirements of the detection system. Although the conductivity detector is still the most popular, other types of detection can be applied for different analytes. These include electrochemical (amperometric, pulsed and integrated amperometric, potentiometric), photometric (UV-Vis, indirect photometric following post column derivatisation, chemiluminescence, refractive index), and fluorescence. 

The detection methods used include spectrophotometry, chemiluminescence, fluorescence, amperometry, conductometry, thermometry and potentiometry with ion-selective electrodes or gas sensors. We have focused our attention only on the electrochemical detectors. Some examples of applications of reactor biosensors with the specification of enzyme used, reactor type and detection system are summarized in Table 5. 

---