Universal Multilayer Assemblies of Graphene in Chemically Resistant Microtubes for Microextraction

Graphene is a new kind of two-dimensional carbon nanomaterial with excellent properties and is promising for solid-phase microextraction (SPME). Plastic microtubes such as poly(tetrafluoroethylene) (PTFE) and poly(ether ether ketone) are ideal substrates for in-tube SPME. However, immobilization of graphene layers onto these materials is still a problem due to their nature of chemical resistance. In order to solve the problem, we proposed a novel method based on universal mussel-inspired polydopamine (PD) and layer-by-layer assembly of graphene in this work. To make a graphene assembly layer inside PTFE, the strategy includes two major steps. First, a PD layer is made on the PTFE surface by noncovalent interaction. Second, multilayer graphene is assembled on the PD layer by covalent interaction. By repeating these two steps, a functional graphene oxide (FGO)-modified PTFE tube with a controllable number of layers can be obtained. Morphology of the multilayer structure of graphene has been confirmed by scanning electronic microscopy. Formation of the covalent layer has also been characterized by Foourier transform infrared and X-ray photoelectron spectroscopy. It is very interesting that (FGO-PD)3-PTFE shows exceptional efficiency for SPME. Enrichment from 1082- to 2331-fold was achieved for six polyaromatic hydrocarbons (PAHs). An online SPME-HPLC-fluorescent detection method has been developed on the basis of (FGO-PD)3-PTFE. For qualitative analysis of PAHs, the method has low limits of detection of 0.05-0.1 pg/mL, which is significantly lower (up to 1000 times) than that reported in literature. The method shows wide linear range (0.3-200 pg/mL), good linearity (R(2) ≥ 0.9968), and good reproducibility (relative standard deviation < 3.4%). The method has been applied to determine PAHs in environmental samples. Good recoveries were obtained, ranging from 85.1% to 96.7%.