Model protein detection using antibody-immobilized tapered fiber optic biosensors (TFOBS) in a flow cell at 1310 nm and 1550 nm

In a recent study, we reported for the first time the detection of a model protein Bovine Serum Albumin (BSA) using antibody-immobilized tapered fiber optic biosensors (TFOBS) at 1550 nm under stagnant condition, with a detection limit of 10 fg/mL. In this study, we examine the detection of BSA in a flow cell configuration because flow reduces non-specific adsorption of contaminating proteins, eliminates transmission changes due to mechanical movements, and allows for quick switching between samples.TFOBS were fabricated with waist diameters of 5–10 μm and total lengths of 1000–1200 μm. They were housed in a specially constructed holder which served as a flow cell. The non-specific response of the TFOBS was measured by flowing in aqueous glucose solutions of various refractive indices at 0.5 mL/min. Detection experiments were conducted by immobilizing antibody to BSA on TFOBS surface, and then exposing them to 1 pg/mL–10 ng/mL of BSA at 0.5 mL/min and measuring the transmission at 1310 nm and 1550 nm. In addition, 1 pg/mL of BSA in the presence of 1 pg/mL of Ovalbumin (OVA) was measured successfully in the same apparatus.The transmission of TFOBS is a function of refractive index of the liquid surrounding the taper, and depends on the wavelength. Both pure BSA and BSA in the presence of OVA were detected in the flow cell arrangement. The transmission response and attachment rates were quantified and found to be similar for the two cases.