Non-enzyme Sensors Based On Nanocomposites For The Detection Of Small Biomolecules

Since glucose enzyme biosensor was first proposed by Clark in1962, enzyme biosensor because of its high sensitivity and good selectivity has been received considerable attention and widely applied in various fields including clinical diagnosis, environment monitoring and food industry. However, the enzyme is easy to inactivation in the loading process due to its poor internal structure as well as the influence of the environment temperature. This makes the stability of the enzyme sensors are not ideal. Therefore, constructing non-enzyme sensors has become a hot research.Small biomolecules play a very important role in human body. For example, dopamine (DA) is an important neurotransmitter. Abnormal levels of DA will lead to brain disorders such as Parkinson and schizophrenia diseases. A lot of small biomolecules widely coexist in our body fluids such as ascorbic acid (AA), uric acid (UA) nitrite ion (NO2-) and so on. These substances are electrically active. At bare electrode, the oxidations of these substances need high over-potential. Besides, the selective determination of AA, DA and UA is impossible because their oxidation potentials are very close. Furthermore, the stability and reproducibility of the bare electrode will be not so satisfied because of the surface fouling caused by the adsorption of oxidized products of AA on electrode surface. Therefore, how to build a modified electrode for simultaneous detection of the coexistence of small biological molecules appears extremely urgent. In recent years, nanomaterials due to its unique electrochemical properties, large specific surface area, high surface free energy, and good biological compatibility have been widely applied in the field of sensor. Based on the above consideration, in this paper, we have constructed a variety of non-enzyme sensors with high sensitivity and selectivity for the detection of small biomolecules.The main works are included as follows:1. Amperometric biosensor for nitrite and hydrogen peroxide based on hemoglobin immobilized on gold nanoparticles/polythionine/platinum nanoparticles modified glassy carbon electrodeIn this work, first, Pt nanoparticles (PtNPs) were electrodeposited on the glassy carbon electrode (GCE) surface, which promoted the electron transfer and largely enhanced the loading of poly-thionine (PTH). Subsequently, thionine (TH) was electropolymerized on the PtNPs/GCE. TH is not only a good mediator, in acidic solution it is also can effectively put NO2-adsorption to the surface of the electrode and catalysis oxidation in certain potential. Followed gold nanoparticles (AuNPs) were assembled onto the PTH film to improve the absorption capacity of hemoglobin (Hb) and further facilitate the electron transfer. Finally, Hb was immobilized onto the electrode through AuNPs. Cyclic voltammetry (CV) and scanning electron microscopy (SEM) have been used to characterize the fabrication process of the sensing surface. Under the optimum conditions, the biosensors can be used for the determination of NO2-in the concentration range from70nmol·L-1to1.2mmol·L-1, and of H2O2in the range from4.9μmol·L-1to6.8mmol·L-1. The detection limits (S/N=3) are20nmol·L-1and1.4μmolL-1, respectively. The biosensor exhibits good analytical performance, acceptable stability and good selectivity.2. Simultaneous voltammetric determination for DA, AA and NO2-based on graphene/poly-cyclodextrin/MWCNTs nanocomposite platformIn the present work, cyclodextrin prepolymer (pre-CD) was prepared first. Then it mixed together with CD, graphene sheets (GS) and multiwall carbon nanotubes (MWCNTs) by ultrasonication. CD cross-linked pre-CD (CDP) displays excellent film forming ability, and the mixture overcame the shortcomings of the CD soluble in water, which made the electrode more stable. MWCNTs effectively inhibited the stacking of individual GS and enhanced the utilization of GS based composites. The host-guest chemical reaction ability of CD and p-p stacking interaction between detected molecules and GS-MWCNTs surface were considered as the main reasons of the successfully simultaneous detection of DA, AA and NO2-. Cyclic voltammetry (CV), scanning electron microscopy (SEM) and different pulse voltammetry (DPV) were employed to characterize the biosensor. The linear response range for AA, DA and NO2-were5μmol·L-1-0.48mmol·L-1,0.15-21.65μmol·L-1and5μmol·L-1-6.75mmol·L-1, respectively and the detection limits were1.65μmol·L-1,0.05μmol·L-1and1.65μmol·L-13. Carbon nanotubes incorporated with sol-gel derived La(OH)3nanorods as platform to simultaneously determine ascorbic acid, dopamine, uric acid and nitriteThe rare earth materials with excellent optical, electrical, magnetic and other properties, widely used in the field of catalysts, lasers and light emitting materials, but in the field of electrochemistry its reports were less. In this work, we prepared a novel material, sol-gel derived La(OH)3nanorods (La(OH)3NRs) with excellent film forming ability and good electrical conductivity. MWCNTs can disperse well in its solution, which can effectively improve the electrode stability and the response performance. Cyclic voltammetry (CV), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were employed to characterize the sensor. Under optimal conditions, the linear response range for AA, DA, UA, and NO2-were0.5μmol·L-1-1.46mmol·L-1,50nmol·L-1-35.36μmol·L-1,50nmol·L-1-0.79mmol·L-1, and0.55μmol·L-1-0.72mmol·L-1, respectively and the detection limits were1.67μmol·L-1,1.67nmol·kL-1,1.67nmol·L-1, and0.18μmol·L-1. The sensor demonstrated well stability, high selectivity and sensitivity. More importance, this material can be extended to construct other electrochemical sensors by the immobilization of enzymes and antibodies.