Electrochemical Biosensors Based On Functionalized Graphene Doped With Nanoparticles For Organophosphates Detection

Electrochemical acetylcholinesterase(ACh E) biosensors are widely used for detecting organophosphorus pesticides(OPs). In the fabrication of ACh E biosensors, the modified materials play an important role in improving the sensitivity and response signal of the biosensors. Ionic liquid functionalized graphene(IL-GR) doped with noble metal or metal oxide nanoparticles showed multiple advantages of graphene, ionic liquids, noble metal or metal oxide nanoparticles, which exhibited some tremendous characteristics such as large surface area, good electrical conductivity, high biocompatibility and catalytic performance. In this paper, IL-GR doped with Co3O4, Au-Pd and Ni O were chosen as modified materials, and a series of fast and sensitive electrochemical ACh E biosensors with good performance were fabricated for OPs detection. The main contents of this paper are as follows:1. Ionic liquid modified graphene(IL-GR) and Co3O4 were first dispersed in chitosan(CHI) and form IL-GR-Co3O4-CHI dispersion, then IL-GR-Co3O4-CHI and acetylcholinesterase(ACh E) was mixed evenly and was coated on the glass carbon electrode. Finally, glutaraldehyde was used as cross-linker to immobilize the ACh E, and a novel biosensor(ACh E-IL-GR-Co3O4/GCE) for detecting dimethoate was developed. The IL-GR and Co3O4 nanoparticles were synthesized and characterized by Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD) and Transmission electron microscopy(TEM), respectively. The nanocomposite of IL-GR and Co3O4 exhibited a strong synergetic effect on improving the performance of the biosensor. Linear relationship between the inhibition percentage(I%) and logarithm of concentration of dimethoate was found in the range of 1.0×10-15 ~ 1.0×10-6 mol/L and 1.0×10-4 ~ 4.0×10-4 mol/L, with a detection limit of 5.0×10-16 mol/L(S/N=3). The easily prepared electrochemical sensor had favorable stability and sensitivity, thus providing a promising tool for OPs detection.2. A fast and stable organophosphate pesticides(OPs) biosensor with enhanced sensitivity was developed for the detection of OPs by using Au-Pd bimetallic nanoparticle and ionic liquid functionalized graphene-chitosan nanocomposites(Au-Pd/IL-GR–CHI). An electrodeposition method was firstly applied to form Au-Pd nanoparticles on the surface of methods. The electron transfer resistance of the Au-Pd/IL-GR–CHI modified electrode was smaller than that of the Au/IL-GR–CHI(or Pd/IL-GR–CHI) modified electrode, indicating that the presence of Au-Pd/IL-GR–CHI hybrid nanocomposites on the electrode surface could improve the reactive site, reduce the interfacial resistance, and make the electron transfer easier. The Au-Pd/IL-GR–CHI hybrid nanocomposites with excellent conductivity, catalysis and biocompatibility offered an extremely hydrophilic surface for ACh E adhesion. Under optimal conditions, based on the inhibition of organophosphate pesticides(OPs) on the ACh E activity, using phorate as a model compound, the biosensor detected phorate in the linear range from 5.0×10-16 to 2.5×10-13 mol/L and from 4.9×10-13 to 9.5×10-6 mol/L, with a detection limit of 2.5×10-16 mol/L(S/N=3).3. Electrochemical deposition of Ni O on a glassy carbon electrode surface was first completed, then IL-GR and ACh E were immobilized on the modified electrode via chitosan film-froming effect, and a sensitive ACh E biosensor(ACh E-IL-GR/ Ni O/GCE) for the detection of dimethoate and monocrotophos was fabricated. The synergistic effect of Ni O and IL-GR promoted the rate of electron transfer. The biosensor could be successfully applied for the OPs detection. The inhibition percentages of monocrotophos was proportional to its concentration in the range of 5.0×10-12 to 2.5×10-5 mol/L, with a detection limit of 2.5×10-12 mol/L(S/N=3). And the inhibition percentages of phorate was proportional to its concentration in the range of 5.0×10-12 to 5.0×10-5 mol/L,with a detection limit of 2.5×10-12 mol/L(S/N=3). Meanwhile, the biosensor showed good reproducibility and stability, which plays an important role in the practical application.