(INVITED) Label-Free Detection of Antibodies Using Functionalised Long Period Grating Optical Fibre Sensors

Immunoglobulin A (IgA), IgG, and IgM immunosensors based on long period gratings (LPG) are developed in this work. An LPG has the advantages of being lightweight and small size, which provide possibility to design miniaturized immunosensors for point of care antibody tests. Poly (allylamine hydrochloride) (PAH) and silica nanoparticles (SiNPs) are deposited on the surface of an LPG using a layer-by-layer method. The PAH/SiNPs matrix on the surface of LPG provides a porous surface structure, which is used to immobilise bio-receptors. Anti-IgA, anti-IgG, and anti-IgM are immobilised on the surface of three LPGs to fabricate IgA, IgG, and IgM sensors respectively. The refractive index (RI) on the surface of the LPG increases with antibody concentration, which induces wavelength shifts of the LPG’s attenuation bands. The performance tests of IgA, IgG, and IgM sensors are carried out in the ranges of 10–200 μg/ml, 1–90 μg/ml, and 10–320 μg/ml respectively, and the minimum detected concentrations achieved for all the three sensors are 10 μg/ml. The selectivity of the platform is investigated based on an IgM sensor. Preliminary results obtained in this work demonstrate that LPG-based immunosensors can achieve sufficient selectivity and suitable detection range for human serum testing.