Upconversion luminescence nanoparticles-based lateral flow immunochromatographic assay for cephalexin detection

Because of the near infrared excitation, upconversion luminescence (UCL) rare-earth nanoparticles are very suitable for biological applications in terms of low background interference. NaGdF4:Yb, Er nanoparticles were firstly synthesized through a replacement reaction at high temperature. To improve the upconversion luminescence efficiency, core-shell NaGdF4:Yb,Er@NaGdF4 nanoparticles were then prepared by a seed-mediated method. The core-shell architecture significantly improved the upconversion luminescence and more effectively retained the luminescence during the following phase transfer process by ligand exchange. Upon further coupling with anti-cephalexin monoclonal antibody via click reaction, the resultant upconversion luminescence probe was obtained and used in a lateral flow immunochromatographic assay (LFIA) to detect the antibiotic residue of cephalexin. The results were compared with those achieved by a nanoprobe assay based on gold nanoparticles. More quantitative results were extracted by luminescent intensity analysis. Under optimized conditions, the detection limit of UCL nanoparticles-based LFIA was considerably comparable with gold nanoparticles-based LFIA.