Electrochemical Enzyme-based Biosensors Based On Two Dimensional Nanosheet Composites

Taking advantage of outstanding attributes, such as economical, sensitive, and simple-to-fabricate, in recent decades, quite a number of attentions have been devoted to the integration of bio-recognition elements with electronic elements to fabricate electrochemical biosensors. With outstanding achievements in nanotechnology and nanoscience, nanomaterial-based technology of electrochemical signal amplifications have promising potential on improving both selectivity and sensitivity for electrochemical biosensors. Two dimensional nanomaterials are attracting markedly increasing interest after graphene was prepared from graphite by using the mechanical cleavage method. At present, a lot of neoteric 2D nanomaterials has been used to fabricated electrochemical biosensors and obtained satisfied results. However, with the deepening of the research, scientists had found that the 2D nanocomposites, which was made via the reasonable assembling process, possessed more great electrochemical properties than his separate components, indicating the great collaborative advantage.In this paper, different 2D nanocomposites are used as modifiers to fabricate several electrochemical biosensors.1. Hemoglobin(Hb) was firstly immobilized into Zn2Al-LDH modified with amino functionalized ionic liquid(AFIL) through coprecipitation technique at pH 9.0 to fabricate the enzyme modified glass carbon electrode(AFIL-LDH-Hbcop/GCE) and study the direct electrochemistry of redox protein. The UV-Vis and FTIR spectroscopy of AFIL-LDH-Hbcop composite film illustrated that Hb maintained its natural structure and kept good stability. X-ray diffraction and scanning electron microscopy revealed that AFIL-LDH-Hbcop film had a featured layered structure and a uniform, roughness and porous morphology with Hb being strongly interlocked. Cyclic voltammetric results of AFIL-LDH-Hbcop/GCE showed a pair of well-defined redox peaks in PBS(pH 7.0) at the scan rate of 0.1 V s-1. The modified bioelectrode displayed good electrocatalytic activity toward the reduction of trichloroacetic acid in the concentration. The performance of fabricated electrochemical biosensor was investigated by CV and current-time curve with satisfactory results.2. A novel electrochemical biosensor based on the hybrid of graphene, exfoliated Co2 Al layered double hydroxide(ELDH) and hemoglobin has been fabricated. Transmiss electron microscopy, scanning electron microscopy and X-ray diffraction characterizations clearly exhibited that the ELDH was successfully incorporated with graphene nanosheets, which can greatly enhance its electrochemical performance. The spectroscopic analysis of UV-vis, FT-IR as well as fluorescence spectroscopy powerfully demonstrated that no obvious conformational changes of Hb immobilized on GR-ELDH nanocomposite. The performance of fabricated electrochemical biosensor was investigated by cyclic voltammetry(CV), electrochemical impendance spectra and square wave voltammetry(SWV), and the results showed that GR-ELDH-Hb nanocomposite modified carbon ionic liquid electrode(CILE) exhibited excellent electrocatalytic performance toward trichloroacetic acid.3. A facile method to obtain AFIL-GR-ELDH nanocomposite that were GO-ELDH hybrid covalently functionalized with AFIL was reported-the resulting nanocomposites, without any assistance from polymeric or surfactant stabilizers, can be stably dispersed in water. Then, the obtained nanocomposite was used to immobilize Hb and fabricate biosensor to realise the following electrochemical tests. TEM, SEM, FTIR, XRD and XPS characterization clearly demonstrated the exist of AFIL on the GR nanosheet. The spectroscopic analysis of UV-vis and FTIR indicated that no obvious conformational changes of Hb immobilized on GR-E LDH nanocomposite.4. A novel synthetic path was reported to fabricate a graphene-layered double hydroxide-graphitic-C3N4(GR-LDH-g-C3N4) nanocomposites. Firstly, the nanosheet of graphene oxide(GO) was combined with delaminated LDH layers by the electrostatic attraction. Then, the hydrothermally process was used to reduce GO existed in GO-ELDH hybrid to obtain the gel of GR-ELDH. Finally, the resultant gel product was calcined with melamine and then via a LDH recovery process to obtain the final product of GR-LDH-g-C3N4, which was used to immobilize Hb and fabricate biosensor to realise the following electrochemical tests. The spectroscopic analysis of UV-vis and FT-IR powerfully demonstrated that no obvious conformational changes of Hb immobilized of resultant hybrids. X-ray diffraction and scanning electron microscopy clearly exhibited that g-C3N4 uniformly grew on the layer surface of graphene without any distinct graphene layer restack. The performance of fabricated electrochemical biosensor was been thoroughly investigated by CV and EIS. The results showed that CTS/GR-LDH-g-C3N4-Hb/CILE ternary modified electrode have higher electrochemical performance than their binary counterparts.