Resonance Scattering Assay for Trace Human Chorionic Gonadotrophin Using Gold-platinum Nanoalloy Immunoprobe as Catalyst

In the presence of sodium citrate as stabilizer, a gold-platinum nanoalloy (GP) in the mole ratio of 49∶1 was prepared by using NaBH4 as a reducing agent. The rabbit anti-human chorionic gonadotrophin antibody (RhCG) was labeled by the GP to obtain a stable immune GP probe (GP-RhCG) for the human chorionic gonadotrophin (hCG). In a pH 5.8 NaH2PO4-citric acid buffer solution and in the presence of KCl, the GP-RhCG probe was aggregated un-specifically to big particles that exhibited a resonance scattering (RS) peak at 590 nm. When the hCG was added, the GP-RhCG probe com- bined specifically with the hCG to form a dispersed GP-RhCG-hCG immunocomplex that resulted in the RS intensity de- creasing at 590 nm. The decreased RS intensity (ΔI590 nm) is linear with hCG concentration in the range of 6.67—86.7 ng/mL, with a detection limit of 3.7 ng/mL hCG. The immunocomplex exhibited a strong catalytic effect on the slow Cu2O particle reaction of glucose-Cu(II), and the particles appeared a RS peak at 610 nm. When the hCG concentration increased in the immune reaction system, the immunocomplex concentration increased, and the catalytic product of Cu2O particles increased, which caused the enhancement of RS intensity at 610 nm. The increased intensity (ΔI610 nm) is linear with the hCG concentra- tion in the range of 3.33—133 ng/mL, with a detection limit of 1.7 ng/mL hCG. In addition, the influence of foreign sub- stances on the determination of hCG was examined. The results show that 150 times of L-aspartic acid, urea, BSA, glycine, Ca(II) and Zn(II), 50 times of L-lysine and L-cysteine, 30 times of IgG and IgA, 40 times of IgM did not interfered with the determination of 80 ng/mL hCG. This indicates that this method has good selectivity. The hCG content in the serum sample was analyzed by the GP RS method and GP-catalytic RS method, the results are agreement with those of the chemilumines- cence experiments. Both RS methods are of some advantages including low-cost, simplicity, rapidity, high sensitivity and selectivity.