Simultaneous detection of two tumor markers using silver and gold nanoparticles decorated carbon nanospheres as labels

In this work, a multiplexed electrochemical immunosensor was developed for sensitive detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) using silver nanoparticles (Ag NPs) or gold nanoparticles (Au NPs) coated-carbon nanospheres (CNSs) as labels. CNSs were employed as the carrier for the immobilization of nanoparticles (Ag NPs or Au NPs), thionine (Thi), and secondary antibodies (Ab₂) due to their good monodispersity and uniform structure. Au NPs reduced graphene oxide (rGO) nanocomposites were used as sensing substrate for assembling two primary antibodies (Ab₁). In the presence of target proteins, two labels were attached onto the surface of the rGO/Au NPs nanocomposites via a sandwich immunoreaction. Two distinguishable peaks, one at +0.16 V (corresponding to Ag NPs) and another at −0.33 V (corresponding to Thi), were obtained in differential pulse voltammetry (DPV). The peak difference was approximately 490 mV, indicating that CEA and AFP can be simultaneously detected in a single run. Under optimal conditions, the peak currents were linearly related to the concentrations of CEA or AFP in the range of 0.01–80 ng ml⁻¹. The detection limits of CEA and AFP were 2.8 and 3.5 pg ml⁻¹, respectively (at a signal-to-noise ratio of 3). Moreover, when the immunosensor was applied to serum samples, the results obtained were in agreement with those of the reference method, indicating that the immunosensor would be promising in the application of clinical diagnosis and screening of biomarkers.