Probing solid-liquid interfaces using radiotracer technology: Characterization of functionalized microspheres

This study explores the use of nuclear probes (radiolabeling techniques) for the quantification of available, reactive groups on solid surfaces and their role in the engineering of materials for biosensor applications. Microspheres were synthesized with reactive carboxylate groups as conjugation sites for proteins. The carboxylate groups were reacted with three bifunctional ligands, sarar, aminobenzyl-cyclen, and aminobenzyl-dota. The reaction conditions used were similar to that employed for the conjugation of proteins and optimized for the concentration of reactants (bifunctional ligand and EDC), pH, and time at °21 °C. Of the three bifunctional ligands conjugated to the microsphere, sarar proved to be the most efficient. Optimum reaction conditions employed molar ratios of 1:20:100 for microspheres (estimated carboxylate groups of 1.1 × 10^-7 per milligram of microspheres):sarar:EDC at pH 5.0 for 1 h, followed by ^57/natCo radiolabeling at pH 7.0. The study demonstrates how nuclear probes with high specificity and sensitiviy can provide invaluable information on available reactive sites on solid surfaces at extremely low concentrations (>10^-10 M) in a range of media. More importantly the nuclear probes enable the characterization of the surfaces of new materials in a non-destructive manner under conditions relevant to the engineering of the materials and ultimately the desired biosensor.