We demonstrate the first in-fiber light-induced bioactive biotin-functionalization via photobleaching fluo- rophore-conjugated biotin. Photobleaching the fluoro- phores generated free radicals that bind to the albumin- passivated inner surface of pure silica photonic crystal fiber. The subsequent attachment of dye-conjugated streptavidin to the bound biotin qualified the photo-immo- bilization process and demonstrated a potential for the construction of in-fiber macromolecular assemblies or mul- tiplexes. Compared with other in-fiber bioactive coating methods, the proposed light-induced technique requires only a low-power light source, without the need for addi- tional preactivation steps or toxic chemical reagents. This method, hence, enables a simple and compact implementation for potential biomedical applications.
Label-free, all-fiber immunosensors based separately on Mach–Zehnder interferometry (MZI) and Michelson interferometery (MI) implemented using only single mode fiber (SMF) are proposed and exper- imentally demonstrated. The proposed SMF–MZI and SMF–MI sensors rely on intermodal interference between the core mode and cladding modes to detect ambient refractive index changes due to protein absorption on the cladding–ambient interface. The fiber surfaces were functionalized with self-assembled polyelectrolyte layers (chitosan (CS)/polysodium styrene sulfonate (PSS)). Immunoglobulin G (IgG) was immobilized on the polyelectrolyte layer and anti-immunoglobulin G (anti-IgG) molecular binding events were monitored through measurement of wavelength shifts. The proposed immunosensors exhibit anti- IgG detection sensitivities of 27.37nm/(ng/mm2) and 5.91nm/(ng/mm2) with concentration detection limits of 0.181 nM and 4.941 nM for MZI and MI sensor respectively. The specificities of the sensors were investigated using correlated/non-correlated anti-IgG–IgG pairs. These results demonstrate the feasi- bility of these sensors for various bio/chemical applications such as DNA hybridization detection and immunosensing.
A label-free, layer-by-layer (LBL) modified, fiber- optic interferometry biosensor for real-time affinity-based protein sensing applications has been proposed. The proposed sensor al- lows real-time protein adsorption detection by monitoring inter- ference wavelength shifts, which offers better dynamic range and stability in comparison to current detection of changes in optical in- tensity. With a label-free sensing mechanism, it eliminates issues of progressive leaching of indicators, expensive and time-consuming labeling procedures and undesirable nonspecific interactions with target proteins. The unique Fabry–Perot cavity consists of an LBL coating layer of nanometre thickness deposited on the distal ends of a hollow core cavity spliced to a standard single-mode optical fiber (SMF). This novel configuration allows the LBL sensing el- ement to be enclosed by similar mediums, on both sides of the LBL multilayer film coat, thus surrounded by identical properties such as the same refractive index that improves the sensitivity of the proposed sensor. Furthermore, the LBL coat consisting of chi- tosan and polysodium styrene sulfonate, commonly used in drug delivery and cell culture, indicates good biocompatibility for future in vivo biomedical applications such as immunosensing and DNA hybridization detections.