Biconical tapered optical fiber biosensor for real-time monitoring of bovine serum albumin at femtogram/mL levels on antibody-immobilized tapered fibers

A single-mode tapered fiber optics biosensor was utilized for the real-time attachment of model protein bovine serum albumin (BSA) to the antibody-immobilized surface of the taper. The applied fiber tapers were fabricated with waist diameter of 6-7μm and of 3mm waist length using heat-pulling method. The surfaces of the tapers were modified with an amine group to allow for the formation of a covalent bond between the amine and one of the carboxylic groups of the antibody. The attachment of BSA to the antibody-immobilized surface of the taper at (20-25ºC) temperature was monitored by transmission of a 1558.17nm distributed feedback (DFB) laser through the tapered fiber. While cuvette measurements established that BSA was non-absorbing at 1558 nm showing no significant changes in optical throughput through the cuvette, tapered fibers with antibody-immobilized surfaces showed changes in optical throughput at bulk concentrations down to100 fg/mL of BSA. We postulate that the adsorption of the protein to the tapered fiber leads to changes in the optical characteristics of the taper. This affects the evanescent field leading to changes in optical throughput.