Anti-cortisol was encapsulated in optically transparent sol-gel silica matrices and competitive immunoassays for cortisol were conducted using the antibody-doped silica material as sensing elements. Calibration curves were derived in the physiological relevant range for cortisol of 1 to 100 mg dl 21 . Sensing elements were prepared in both monolith and thin-film forms, and results show that with thin films, accessibility of antigen to the encapsulated antibody was improved leading to a significant reduction in the required assay time. Moreover, non-specific binding to the sol-gel silica matrix was well controlled. ExperimentalReagents Tetramethylorthosilicate (TMOS) was obtained from Sigma-Aldrich Chemical Co. Anti-cortisol was purchased from East Coast Biologics. Cortisol standards in serum were obtained from Beckman Coulter (2 to 60 mg dl 21 cortisol concentration range) and ICN Pharmaceuticals (1 to 100 mg dl 21 cortisol concentration range). For cortisol, 1 mg dl 21 ~27.6 nM. Oregon Green conjugated to cortisol (OG-cortisol) was custom synthesized by Molecular Probes. 1X phosphate buffered saline (PBS) was obtained from Fisher Scientific.

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