Layered graphene nanostructures functionalized with NH2-rich polyelectrolytes through selfassembly: construction and their application in trace Cu(II) detection

Layer-by-layer (LBL) self-assembled graphene nanosheets, noncovalently functionalized with evenly spread-NH2 groups attached on the linear polyelectrolyte of polyallylamine hydrochloride (PAH), were produced successfully. The fabrication process consisted of two steps. At first, completely exfoliated graphite oxide (GO) species were highly stacked on the surface of a pretreated glassy carbon electrode as a result of the sequential adsorption of the cationic layer of PAH and the anionic layer of oxygencontaining GO through electrostatic and/or hydrophobic interactions. Then, the GO species were chemically reduced by a strong reducing agent, NaBH4. The structural morphology and electrochemical properties of the as-prepared graphene-based multilayer LBL composite electrodes were thoroughly characterized by techniques such as ultraviolet visible (UV-vis) spectroscopy, high-resolution X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, and cyclic voltammetry. Combined with differential pulse anodic stripping voltammetry (DPASV), the obtained -NH2 functional group modified nanocomposite electrodes with highly ordered multilayer superconductive graphene showed improved performance for trace detection of heavy metal ions such as Cu(II), resulting in sensitive electrochemical sensors. A linear dynamic range from 0.5 to 50 mu M for Cu( II) was obtained under optimized conditions with a relatively low detection limit (S/N = 3) of around 0.35 mu M. Our results provide valuable insight for the facile design of highly ordered graphene nanostructures with specific functionality of interest in a vast range, leading to a versatile nanoplatform for environmental or biomedical applications.