Electrochemical immunoassay detection limits

Instead of immobilizing the antibody onto the transducer, it is possible to use a bare (amperometric or potentiometric) electrode for probing enzyme immunoassay reactions (42). In this case, the content of the immunoassay reaction vessel is injected to an appropriate flow system containing an electrochemical detector, or the electrode can be inserted into the reaction vessel. Remarkably low (femtomolar) detection limits have been reported in connection with the use of the alkaline phosphatase label (43,44). This enzyme catalyzes the hydrolysis of phosphate esters to liberate easily oxidizable phenolic products. 

A sandwich electrochemical enzyme immunoassay has been described for IgG Alkaline phosphatase was again used as the enzyme label with the conversion of phenyl phosphate to phenol being determined electrochemically by LCEC. A detection limit of 10 pg/mL was reported. 

One of the most exciting new applications for electrochemistry in the last decade has been in the area of immunoassay. With more than a hundred million immunoassays being performed world-wide each year, researchers have begun to carve out new immunoassay strategies which exploit the excellent detection limits that can be achieved with modem electrochemical techniques. 

Because of this lack of resolving power, much electroanalytical research is aimed at providing increased selectivity. This can be accomplished in two ways. First, electrochemistry can be combined with another technique, which provides the selectivity. Examples of this approach are liquid chromatography with electrochemical detection and electrochemical enzyme immunoassay. The second approach is to modify the electrochemical reaction at the electrode to enhance selectivity. This approach is exemplified by modified electrode methods where reaction at the electrode surface is limited beyond mere electrochemical considerations to include physical and chemical properties. The following discussion will illustrate in detail how these approaches can provide analytical techniques with both high selectivity and low detection limits. 

Khan et al have used Ti02-chitosan nanocomposite film for an electrochemical immunoassay protocol. The concept has been demonstrated for a simultaneous immunoassay of rabbit-IgGs, bovine serum albumin protein, Ti02-chitosan nanocomposite film and detection limit of 7.5 mM has been obtained [86],... 

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