Immunosensors additives

Furthermore, research efforts described herein, have resulted in at least a ten-fold improvement in the detection of Clostridium botulinum neurotoxin using a fiberoptic immunosensor. Additionally, the increased sensitivity of the assay by using affinity purified polyclonal antibodies as both the immobilized capture antibodies and the fluorescently labeled antibodies suggests that the investigation into additional assay systems may be worthwhile. 

There are mainly three types of transducers used in immunosensors electrochemical, optical, and microgravimetric transducers. The immunosensors may operate either as direct immunosensors or as indirect ones. For direct immunosensors, the transducers directly detect the physical or chemical effects resulting from the immunocomplex formation at the interfaces, with no additional labels used. The direct immunosensors detect the analytes in real time. For indirect immunosensors, one or multiple labeled bio-reagents are commonly used during the detection processes, and the transducers should detect the signals from the labels. These indirect detections used to need several washing and separation steps and are sometimes called immunoassays. Compared with the direct immunosensors, the indirect immunosensors may have higher sensitivity and better ability to defend interference from non-specific adsorption. 

Immunosensors have been developed commercially mostly for medical purposes but would appear to have considerable potential for food analysis. The Pharmacia company has developed an optical biosensor, which is a fully automated continuous-flow system which exploits the phenomenon of surface plasmon resonance (SPR) to detect and measure biomolecular interactions. The technique has been validated for determination of folic acid and biotin in fortified foods (Indyk, 2000 Bostrom and Lindeberg, 2000), and more recently for vitamin Bi2. This type of technique has great potential for application to a wide range of food additives but its advance will be linked to the availability of specific antibodies or other receptors for the various additives. It should be possible to analyse a whole range of additives by multi-channel continuous flow systems with further miniaturisation. 

The data shown here demonstrate the use of an NIR dye immobilized in a polymer matrix which is sensitive to changes in metal ion concentration and solution pH. Additionally, the utility of NIR dyes in immunosensors has been shown. Although the use of NIR dyes in fiber optic techniques has only recently been demonstrated, the range of potential applications is abundant. As functionalized NIR dyes become commercially available or new, large-scale syntheses are reported, the use of NIR dyes in bioanalytical applications will most certainly expand. 

A disposable immunosensor for AFBi determination in barley has been reported [203], this time using an SPCE bearing surface-immobilised AFBi antigen conjugated to BSA. After incubation of the sensor with the sample and an anti-AFBi monoclonal antibody, the addition of a secondary antibody labelled with alkaline phosphatase, enabled the generation of 1-naphthol from 1-NP, and its detection using DPY. The assay had a reported detection limit of 30pgml 1 in barley. 

Antibody-based, fully automated immunosensors for small molecules have been used to detect explosives (see Refs. [11,12]) and biological warfare agents (see Refs. [13,14]), and can be used to analyse drinking water and extracts at hazardous waste sites (for examples, see Refs. [15-17]). In the following section, we will discuss how the addition of electrochemical detection has broadened the capabilities of such devices. 

---