Silicon microchips with immobilized antibodies were used to develop microfluidic enzyme immunoassays using chemiluminescence detection and horseradish peroxidase (HRP) as the enzyme label. Polyclonal anti-atrazine antibodies were coupled to the silicon microchip surface with an overall dimension of 13.1 x 3.2 mm, comprising 42 porous flow channels of 235-microm depth and 25-microm width. Different immobilization protocols based on covalent or noncovalent modification of the silica surface with 3-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GOPS), linear polyethylenimine (LPEI, MW 750,000), or branched polyethylenimine (BPEI, MW 25,000), followed by adsorption or covalent attachment of the antibody, were evaluated to reach the best reusability, stability, and sensitivity of the microfluidic enzyme immunoassay (microFEIA). Adsorption of antibodies on a LPEI-modified silica surface and covalent attachment to physically adsorbed BPEI lead to unstable antibody coatings. Covalent coupling of antibodies via glutaraldehyde (GA) to three different functionalized silica surfaces (APTES-GA, LPEI-GA, and GOPS-BPEI-GA) resulted in antibody coatings that could be completely regenerated using 0.4 M glycine/HCl, pH 2.2. The buffer composition was shown to have a dramatic effect on the assay stability, where the commonly used phosphate buffer saline was proved to be the least suitable choice. The best long-term stability was obtained for the LPEI-GA surface with no loss of antibody activity during one month. The detection limits in the microFEIA for the three different immuno surfaces were 45, 3.8, and 0.80 ng/L (209, 17.7, and 3.7 pM) for APTES-GA, LPEI-GA, and GOPS-BPEI-GA, respectively.

Fluorescence polarization immunoassay (FPIA) is a homogeneous (without separation) competitive immunoassay method based on the increase in fluorescence polarization (FP) of fluorescent-labeled small antigens when bound by specific antibody. The minimum detectable quantity of FPIAs with fluorescein label (about 0.1 ng analyte) is comparable with chromatography and ELISA methods, although this may be limited by sample matrix interference. Because of its simplicity and speed, FPIA is readily automated and therefore suitable for high-throughput screening (HTS) in a variety of application areas. Systems that involve binding of ligands to receptor proteins are also susceptible to analysis by analogous FP methods employing fluorescent-labeled ligand and HTS applications have been developed, notably for use in candidate drug screening.

A direct competitive enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody has been developed and optimized for detection of aflatoxin B1 (AFB1), and an ELISA kit has been designed. This immunoassay was highly specific, sensitive, rapid, simple, and suitable for aflatoxin monitoring. AFB1 concentrations determinable by ELISA ranged from 0.1 to 10 microg L(-1). The IC50 value was 0.62 microg L(-1). Recovery from spiked rice samples averaged between 94 and 113%. The effect of different reagents on the stability of HRP-AFB1 conjugate solution was studied. The performance of a stabilized enzyme tracer in ELISA was determined and compared with that of a freshly prepared control solution of HRP-AFB(1) conjugate. The results showed that stabilizing media containing 0.02% BSA, 0.1% Kathon CG, and 0.05 mol L(-1) calcium chloride in 0.05 mol L(-1) Tris-HCl buffer (pH 7.2) maintained the activity of HRP-AFB1 at a dilution of 1:1000 for a period of at least 12 months at room temperature whereas the reference conjugate solution without the additives lost its activity within a few days. Several additives were tested for their stabilizing effect on a monoclonal antibody (MAb) immobilized on the surface of polystyrene microtitre plates. It was shown that immobilized MAb, treated with post-coating solutions containing PVA, BSA, and combinations of these substances with trehalose, retained its activity for at least 4 months at 4 degrees C, whereas the untreated MAb-coated plate lost its activity within 2 days.

An immunochromatography (ICG) strip test for rapid detection of atrazine in water samples was developed. A monoclonal antibody (MAb) specific to atrazine was produced from the cloned hybridoma cell (AT-1-M3) and used to develop a direct competitive enzyme-linked immunosorbent assay (DC-ELISA) and ICG strip. MAb conjugated to colloidal gold, and that was applied to the conjugate pad of the ICG strip. The visual detection limit for the ICG strip was 3 ng/mL. This test required only 10 min to get results and one step of sample to perform the assay. The results of water samples spiked with 5, 10, 20, and 50 ng/mL of atrazine by ICG strip were in good agreement with those obtained by DC-ELISA. The ICG strip was sufficiently sensitive and accurate to be useful for rapid screening of atrazine in various water samples.