Abstract: In pH 7.4 Na₂HPO₄-NaH₂PO₄ buffer solution with the presence of human chorionic gonadotropin peptide (HCGP) probe, the AgNPs can be aggregated to bigger AgNPs clusters. However, AgNPs can be well dispersed into this solution when the human chorionic gonadotropin (HCG) is added to form stable HCGP-HCG composite. The well-dispersed AgNPs exhibits catalysis on the reaction of H₂O₂ reducting HAuCl₄ into AuNPs which appeares a strong surface plasmon resonance (SPR) peak at 550 nm. With the increase of HCG concentration, the SPR peak increases linearly at 550 nm. The increased SPR absorption (ΔA_{550 nm}) is linear to HCG in the range of 0.25～50 μg/L, with a regression equation of ΔA_{550 nm}=0.012 4C+0.02,a correlation coefficient of 0.987 8, and a detection limit of 0.2 μg/L. Thus, a simple, low-cost and sensitive nanosilver-catalytic SPR spectrometry was developed for the determination of HCG.

Key words: peptide probe, human chorionic gonadotropin, AgNPs, nanocatalysis, SPR absorption