An ultrasensitive immunosensor based on cellulose nanofibrils/polydopamine/Cu-Ag nanocomposite for the detection of AFP

• ● An enzyme-free immunosensor is developed for ultrasensitive detection of AFP. • ● CNFs/PDA/Cu-Ag nanocomposite exhibits high peroxidase-like catalytic activity. • ● This constructed immunosensor has a wide linear range and a low detection limit. • ● The novel immunosensor offers an approach for tumor markers in clinical diagnosis. In this work, an ultrasensitive immunosensor for amperometric determination of alpha-fetoprotein (AFP) was developed utilizing Ag and Cu nanoparticles on polydopamine (PDA) functionalized cellulose nanofibrils (CNFs) composite (CNFs/PDA/Cu-Ag) as signal amplifier. PDA was first prepared by self-polymerizing of dopamine, and then was adsorbed on CNFs. The obtained CNFs/PDA was applied as substrate to electrolessly deposit Cu-Ag nanoparticles, using NaBH 4 as reducing agent. The structure and morphology of the synthesized CNFs/PDA/Cu-Ag nanocomposite were analyzed through Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, particle size analyzer and transmission electron microscopy. The CNFs/PDA/Cu-Ag modified glassy carbon electrode can fix AFP antibody (Ab), and further capture AFP specifically. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the assembly process of immunosensor. The immunoreaction was amplified by electrocatalytical reduction of H 2 O 2 on Cu-Ag nanoparticles, through which AFP was quantitatively detected. The developed sensor exhibits wide linear range of 0.01−100 ng mL −1 (R 2 = 0.9963) with low detection limit of 4.27 pg mL −1 (S/N = 3). In addition, it has been used for the detection of AFP in human serum, manifesting its preeminent application prospect in early liver cancer diagnosis.