Layer-by-Layer Assembly of Two-Dimensional Monolayer Films of Gold Nanoparticles for Electrochemical Determination of Melamine

L-Cysteine (L-Cys) and two-dimensional monolayer films of gold nanoparticles (2D MFGS) were employed to modify gold electrodes to build uniform and stable multilayer films by layer-by-layer (LbL) self-assembly, denoted by Au/(L-Cys/2D MFGS)n (n = number of layers). Electrochemical measurements showed that the specific surface area and current amplification capacity of the modified electrode increased with the value of n. In addition, considering the orderliness inside the multilayer 2D MFGS assembly and experimental accessibility, Au/(L-Cys/2D MFGS)n=4 was selected to be the working electrode and dopamine (DA) as the signal quantification molecule for the indirect detection of melamine (MA). The results showed that the oxidation current of DA was inhibited due to the competitive adsorption of melamine upon the working electrode. Under the optimal conditions, the decrease of the dopamine peak anode current is proportional to the melamine concentration from 10−12 to 10−3 M with a detection limit of 0.13 pM. The results demonstrate the potential of 2D MFGS for applications in food and biological analysis. The scheme for fabricating the multilayer electrodes is convenient and environment-friendly, without expensive instrumentation or complex modifications.