Charge-coupled devices assays

Fig. 5 NRL Array Biosensor mixed format immunoassays (modified from [119]). Schematic of (a) the sandwich and (b) the competitive immunoassay fonnats used in the detection of the Campylobacter jejuni and aflatoxin Bi (AFBi), respectively, (a) Sandwich format antigen captured by the immobilized antibody then quantified by passing a second, fluorescently labeled, antibody over the surface, (b) Competitive format competition for binding sites on the fluorescently labeled antibody occurs between the unlabeled antigen in solution and the surface-bound antigen analog, (c) Final charge-coupled devices image taken with the NRL Array Biosensor of a waveguide exposed simultaneously to the C. jejuni (5 x 10" cfu/mL) sandwich assay (SAND) and the aflatoxin Bj (AFBi-1 ng/mL) competitive assay (COMP) in various combinations...

Chemiluminescent assays are conventionally monitored using photomultiplier-based instruments. However, portable instruments are becoming available that use as photodetectors silicon photodiodes, charge-coupled devices, and instant photographic or x-ray film (58, 63-68). Spacially resolved, quantitative light measurements are pcirticularly advantageous for assays based on membranes or microtiter plates. 

Areas in which technological innovations have been accomplished include detection instruments [ranging from small portable luminometers (M3) to camera-type detectors (B32, K30) and charge-coupled devices (L3)], data analysis (E3, SI2), and assay formatting, e.g., immunofiltration (HI6). The so-called camera luminometers (B32) offer the joint advantages of ease of use, portability, and detectability without an electrical power supply. With fast film such as Polaroid 612 (20,000 ASA), exposure times can be as short as 5 sec. Examples of assays using enhanced chemiluminescence and Polaroid 612 film include a-fetoprotein (L9), albumin (L8), immunoglobulins and transferrin (J3), and ferritin (07). 

A. Dzgoev, M. Mecklenburg, B. Xie, A. Miyabayashi, P.O. Larsson, B. Danielsson, Optimization of a Charge Coupled Device Imaging Enzyme Linked Immunosorbent Assay and Snpports for the Simnlta-neous Determination of Mnltiple 2,4-D Samples , Anal. Chim. Acta, 347,87-93 (1997). 

Measurements are generally performed over the whole surface of the array (10) and changes in reflected intensity generally detected using a CCD (charged coupled device) camera (see Fig. 3). SPRi can also be used to assay kinetics by following the reflection pattern over time. 

Electrochemical immunoassays include a wide variety of devices based on the coupling of immunological reactions with electrochemical transduction. All of them involve the immobilization of an immunoreagent component on the surface of the electrode transducer. Electrochemical detection is based on the direct intrinsic redox behavior either of an analyte species or of some reporter molecule. For the detection no expensive equipment is needed, with the measurement of either a simple current or a voltage charge. Different electrochemical detection strategies are used, but ampero-metric detection is most widely used. Potentiometric and conductometric detection are applied in different assays as well. 

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