Immobilization of specific monoclonal antibody on Au nanoparticles for hGH detection by electrochemical impedance spectroscopy

A selective and sensitive electrochemical impedance immunosensor based on immobilization of a specific monoclonal antibody on Au nanoparticles modified gold electrode was developed for determination of human growth hormone (hGH). Colloidal gold nanoparticles were coated on the gold electrode through the thiol groups of 1,6-hexanedithiol monolayer as a cross-linker. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were utilized for characterization of various coating layers. The relative charge transfer resistance of the hGH antibody/Au-colloid/1,6-hexanedithiol modified gold electrode changes linearly with the concentration of the human growth hormone (hGH) solutions. The limit of detection (LOD) was about 0.64 pg mL−1 and the linear dynamic range was obtained from 3 to 100 pg mL−1. The affinity of hGH toward immobilized antibody was calculated to be 4.1 × 1011 M−1 by the slope of the calibration curve. The proposed immunosensor might be used as an accurate and applicable tool for specific diagnosis and evaluation in paraclinical tests, replacing the routine invasive and hazardous radio-immunoassay (RIA) method.