This paper describes the design of new controlled delivery systems consisting of a mesoporous support functionalized on the pore outlets with a certain hapten able to interact with an antibody that acts as a nanoscopic cap. The opening protocol and delivery of the entrapped guest is related by a displacement reaction involving the presence in the solution of the antigen to which the antibody is selective. As a proof-of-the-concept, the solid MCM-41 was selected as support and was loaded with the dye [Ru(bipy)(3)]Cl(2). Then a suitable derivative of the hapten 4-(4-aminobenzenesulfonylamino)benzoic acid was anchored on the outer surface of the mesoporous support (solid S1). Finally the pores were capped with a polyclonal antibody for sulfathiazole (solid S1-AB). Delivery of the dye in the presence of a family of sulfonamides was studied in phosphate-buffered saline (PBS; pH 7.5). A selective uncapping of the pores and dye delivery was observed for sulfathiazole. This delivery behavior was compared with that shown by other solids that were prepared as models to assess the effect of the hapten and its interaction with antibody in the dye delivery control in the presence of the antigen.

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The state of the art of immunoanalysis for the determination of tetracycline and sulfonamide residues in food products is reviewed. Special attention is paid to the design and synthesis of haptens, providing an overview of the efforts spent on developing antibiotic screening methods to determine residue levels in agreement with the legislation. The results and observations published, focused on tetracycline and sulfonamide enzyme-linked immunosorbent assays, are discussed.

A highly sensitive and specific enzyme-linked immunosorbent assay has been developed for detection of sulfathiazole (STZ, 4-amino- N-thiazol-2-yl-benzenesulfonamide). A set of haptens was synthesized in order to produce polyclonal antibodies against sulfonamides. Two ELISA formats (antibody-coated and conjugate-coated) were also investigated using all the serum/coating conjugate combinations that showed specific recognition. The developed ELISA succeeded in detection of STZ at concentrations as low as 0.03 ng mL(-1) over a measurable range of 0.12-6.71 ng mL(-1). Selectivity studies have demonstrated that other sulfonamides do not interfere significantly (<10%) with analysis of STZ by this immunochemical technique. Analysis of spiked bee honey samples by the developed ELISA method showed recoveries were good. The selectivity and sensitivity (IC(50)=1.6 ng mL(-1)) make it a suitable screening method for determination of low levels of STZ in food samples.