Photothermal lateral flow immunoassay using microfiber long-period grating

Abstract

Paper-based biosensors are important analytical tools in biological and chemical fields. To increase the detection limit and range, here we demonstrated a microfiber long-period grating (mLPG) based biosensor for lateral flow immunoassay (mLPG-LFIA). Compared to conventional paper-based biosensor, the mLPG with strong evanescent wave functions as an ultrasensitive tool for detecting the refractive index changes induced by the localized plasmonic heating of antibody-conjugated gold nanoparticles. The LFIA concentration level is encoded into the refractive index modulation and can be subsequently read by measuring the spectral shift of the mLPG. As proof-of-concept demonstration, quantitative analysis of heavy-metal chromium-ion concentrations ranging from of 0.195 to 200 ng/mL is performed, and a detection limit of 0.219 ng/mL is achieved. The proposed technique is sensitive, easy-to-use, and can serve as a powerful tool to analyze trace chemicals or biochemicals for application in the area of medicine, foods safety and environment monitoring.