Competitive immunoassay systems

FIGURE 5.2 Schematic representation of (a) competitive and (b) non-competitive immunoassay formats. 

FIGURE 53 A schematic illustrating a competitive immunoassay format used for the detection of estradiol. (Reprinted from [11] with permission from Elsevier.) 

Electrochemical Sensors, Biosensors and Their Biomedical Applications 

Competitive immunoassays may also be used to determine small chemical substances [10, 11], An electrochemical immunosensor based on a competitive immunoassay for the small molecule estradiol has recently been reported [11]. A schematic diagram of this immunoassay is depicted in Fig. 5.3. In this system, anti-mouse IgG was physisorbed onto the surface of an SPCE. This was used to bind monoclonal mouse anti-estradiol antibody. The antibody coated SPCE was then exposed to a standard solution of estradiol (E2), followed by a solution of AP-labeled estradiol (AP-E2). The E2 and AP-E2 competed for a limited number of antigen binding sites of the immobilized anti-estradiol antibody. Quantitative analysis was based on differential pulse voltammetry of 1-naphthol, which is produced from the enzymatic hydrolysis of the enzyme substrate 1-naphthyl phosphate by AP-E2. The analytical range of this sensor was between 25 and 500 pg mL of E2. 

There are many other examples of competitive electrochemical immunoassays and immunosensors for detecting clinically important analytes [12-14]. Despite simplicity, a disadvantage of competitive immunoassays is that labeling the analyte may reduce, or totally remove, its binding affinity for antibody. This would occur if the analyte were labeled at a site that is closely associated with an epitope. 

---

Competitive immunoassay systems 5.3.2 Non-competitive immunoassay systems... 

---