Quantitative detection of tetracycline residues in honey by a simple sensitive immunoassay.

Tetracyclines (TCs) are widely used for prevention and control of infectious diseases and have a great activity against variety of Gram-positive and Gram-negative bacteria. Due to the widespread use of TCs in animal husbandry, it can lead to an increase the risk of TCs remaining in human food. To protect consumers, many countries have set acceptable tolerance levels for these drugs. Therefore, it is necessary to establish a suitable analytical technique with specificity, sensitivity and simplicity. The biotin-avidin mediated ELISA method was performed to determine TC residues in honey quantitatively. By using PBS-EDTA assay buffer at pH 7.2, a honey solution of TC standard was prepared and diluted. And no additional pre-treatment of sample was required in this method. The limit of detection and limit of quantitation of the optimized method were 3.98 x 10(-10)M (0.19 mugL(-1)) and 7.94 x 10(-10)M (0.38 mugL(-1)), respectively, and the dynamic range was from 1.52 mugL(-1) to 152 mugL(-1) of TC in honey. No cross-reactivity was observed with the structurally similar compounds, and mean percent recoveries of TC spiked in honey ranged from 95% to 101%. Compared to other methods, this method was superior in terms of detection limit, dynamic range, and % recovery with simple sample-preparation.

Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum.

A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 microg mL(-1) of BSA-DA and 1/7500 dilution of anti-DA antibody. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0x10(-9) M (0.19 microg L(-1)) and five orders (3.2x10(-8) M to 3.2x10(-3) M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient (R(2) = 0.9947): Abs. (in serum) = 0.6128 x Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.