Highly sensitive detection of rabbit IgG by electron spin resonance using CuS nanoparticles as probe

Abstract Water soluble copper sulfide (CuS) nanoparticles were synthesized using l -cysteine as the ligand. Multiple biotins were conjugated to the antibody of rabbit IgG, and the streptavidin was attached to the CuS nanoparticles. The Cu2+ ions enclosed in the nanoparticles were used as the electron spin resonance (ESR) probes and detected with ESR spectrometer. The immunoassay reaction was resulted in the formation of the coating antibody attached to the microplate well, the detecting antibody labeled with the biotins, and the streptavidin attached to the CuS nanoparticles. After the immunoassay reaction was performed, large amount of Cu2+/Cu+ ions inside the nanoparticles were released with the help of diethyldithiocarbamate (DDC) and the Cu2+-DDC complex formed. The Cu2+-DDC complex was extracted into n-butanol, which was used as the analytical sample. Both ESR and UV–vis signals were collected for the analytical sample. The double logarithm standard curve was well simulated with a linear regression equation. The limits of detection of the rabbit IgG were 1.76 pg/mL and 2.36 pg/mL by ESR and UV–vis method, respectively. The detection range using ESR as the detector was from 8.8 pg/mL to 500 ng/mL, covering almost 5 magnitude orders of the rabbit IgG concentrations. The rabbit serum was analyzed and the rabbit IgG concentration was found to be 7.76 mg/mL. The reproducibility of the present method was good enough with the intra-assay error within 3.4 % and the inter-assay error within 11.2 %. The spiked serum samples were analyzed and the experimental results indicated that the recoveries were from 108.2 to 113.7%.