Coverage degrees of colloids on electrochemical electrodes and signal amplification for anti-citrullinated peptide antibody detection

Gold nanoparticles (AuNPs) have been used to increase the power of electrochemical biosensors. However, densities and pattern distributions of AuNPs colloids have not been determined yet. In this report, we attempt identifying coverable densities of AuNPs on interdigitated electrodes (IDEs) and increasing the sensing signal by using cyclic antigen (CCP)-coated-AuNPs in impedance biosensors. IDEs were covalently functionalized with CCP-coated AuNPs and used for detection of anti-CCP antibody (ACPA), a remarkable biomarker for rheumatoid arthritis. 36% and 82% of ACPA in human commercial serum were captured by a low CCP (300 CCP per 40-nm nanoparticles) and high CCP (17 × 10⁵ CCP per 40-nm nanoparticles) densities of colloids, respectively. Coverage of the colloids on gaps between two digits of IDEs were observed about at 2.7 × 10⁶ AuNPs (30 nm) per 1 μm² for low signal-to-noise ratio (SNR). The enzyme-catalyzed deposition of silver nanocrystal increased the SNR of the impedance signal up to 7.8 folds of magnitude higher than un-deposited counterparts. Sensitivity and limit of detection were determined at 1.3 ng/mL and 0.12 ng/mL, respectively, at a frequency 900 kHz in the range of 200–2000 kHz. Finally, Principal Component Analysis (PCA) showed the ability of the biosensor to follow variation over time of the number of CCP and therefore also the quantify of ACPA in the samples.