Studies Of Electrochemical (Bio) Sensors Based On Novel Micro/Nano-materials

Nanomaterials, with their size in the range of 1-100 nm, have recently become one of themost exciting forefront fields in material science. Due to their small size, these materialsexhibit quanta-size effect, small-size effect, surface effect and tunneling effect that differfrom both bulk material and the individual atoms from which they comprised. With theseunique properties, they are widely used in the fields of catalysis, optical absorption,medicine, magnetic medium, new materials synthesis and particularly attractive in sensorapplications. Introduction of nanomaterials to the system of electrochemical sensors andbiosensors is of considerable interest, since they can play an important role in improvingthe sensor performance due to their large specific surface area, good conductivity specialcatalytic property and excellent biocompatibility.In chapter 2, an enzyme-free glucose sensor has been developed using a threedimensionalinverse-opal gold film electrode (3DGFE) obtained by electrochemicaldeposition of gold in the interspaces of polystyrene templates. The gold films werecharacterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Theelectrochemical oxidation of glucose in the presence of interferents (ascorbic acid, and so on) at different operating potentials on the 3DGFE has been investigated in detail. A lowoperating potential of -0.30 V was chosen for glucose detection, since the interferencecould be well avoided at this potential, whereas the current response for glucose oxidationwas still sensitive. The amperometric response of the sensor increased with the increase ofglucose concentration with a linear range of 5×10-6 ~ 10-2 mol/L and a detection limit of3.2μmol/L (signal-to-noise ratio of 3). The glucose sensor exhibited a high sensitivity of46.6μA (mmol/L)-1 cm-2, which could be ascribed to the unique surface structure of thethree-dimensionally interconnected porous structured gold films. The sensor with highsensitivity, good selectivity and stability is attractive for the practical glucose detection.In chapter 3, Pt-Pb nanowire array was directly synthesized by electrochemicaldeposition of Pt-Pb alloy into the pores of macroporous polycarbonate template andsubsequent chemical etching of the template. The morphology and the composition of thePt-Pb nanowires were characterized by scanning electron microscopy (SEM) and X-rayphotoelectron spectroscopy (XPS), respectively. Cyclic voltammetry (CV) was used toevaluate the electrochemical performance of the Pt-Pb nanowire array electrode. Directglucose oxidation at such Pt-Pb nanowire array electrode was investigated detailedly bydiscussing the effect of the structure and materials of the electrode on electrocatalyticoxidation of glucose. As a result, we found that the Pt-Pb nanowire array electrode with athree-dimensional structure exhibited high electrocatalytic activity to glucose oxidation inneutral condition and could be used for the development of nonenzymatic glucose sensor.To effectively avoid the interference coming from ascorbic acid, a negative potential of -0.20 V was chosen for glucose detection, and the sensitivity of the sensor to glucoseoxidation was 11.25μA (mmol/L)-1 cm-2 with linearity up to 11 mmol/L, and a detectionlimit of 8 ?mol/L estimated at a signal-to-noise ratio of 3.Mesoporous silicas (MPSs) due to their good mechanical, thermal, chemical stability and large surface area have been proven to be promising as biomaterial immobilizationmatrix. It is worth noting that both the proper surface characteristics of the MPSs and goodmatching of the sizes of the enzyme molecules to the pore diameters of the MPSs arenecessary to the immobilization of enzyme. Unless the two factors are satisfied, theimmobilization of enzymes on MPSs will hardly reach. In addition, the poor conductivityof MPSs is also an important drawback of the materials, which might influence theperformance of the biosensor in amperometric detection. Gold nanoparticles (GNPs) havebeen exploited in biomolecule immobilization. Thus, the introduction of GNPs to MPSs isexpected to conquer the drawbacks of MPSs in enzyme immobilization. In chapter 4, goldnanoparticles-mesoporous silica composite (GNPs-MPS) is developed as a novel enzymeimmobilization matrix for biosensor construction. The mesoporous silica SBA-15 ischosen and the GNPs-SBA-15 is formed from AuCl4- adsorbed H2N-SBA-15 by NaBH4reduction. The synthesis process of the composite is monitored by UV-vis spectroscopyand the product is characterized by transmission electron microscopy (TEM) measurement.An amperometric glucose biosensor is built by immobilizing IO4--oxidized-glucoseoxidase (CHO-GOD) on GNPs-MPS modified Au electrode using 2-aminoethanethiol as across-linker. Cyclic voltammetry (CV) and amperometry are employed to investigate thecatalytic behavior of the biosensor to the oxidation of glucose. As a result, the biosensorexhibits an excellent bioelectrocatalytic response to glucose with a fast response time lessthan 7 s, a broad linear range of 0.02～14 mmol/L , high sensitivity of 6.1μA (mmol/L)-1cm-2, as well as good long-term stability and reproducibility. These performances could beascribed to the GNPs-MPS's features, such as excellent conductivity, large surface areaand good biocompatibility.The design, fabrication, study and application of nanoparticle-based nanostructuredfilms are currently intensely investigated research areas in materials chemistry. Thepotential utility of such thin films includes catalysis, optics, electrics and biosensors. The electrostatic layer-by-layer assembly of nanoparticles and polyelectrolytes is regarded asone of the most simple and versatile method for the construction of ultrathin organizedmultilayers. One of the key advantages of this approach has proved to be a rapid andexperimentally very convenient way to produce complex layered structures with precisecontrol of layer composition and thickness. However, the main defect of the multilayerfilms from electrostatic force is less stability toward polar solvents or electrolyte aqueoussolution, which limits its application range. However, electrostatic layer-by-layerassembled multilayers containing diazo-resins can be converted to covalent bonding at theinterfaces by UV irradiation. This method combines the simplicity of the ionic selfassemblytechnique and high stability of the covalently attached multilayer films. Inchapter 5, by using an ionic layer-by-layer self-assembly technique, the fabrication ofhighly stable diazo-resins/colloidal gold nanoparticles multilayer films on quartz wafer, Sislide and glassy carbon electrodes (GCEs) was achieved by the UV irradiation of layer-bylayerself-assemble multilayer films consisting of diazo-resins (DAR) and citrate-cappedcolloidal gold nanoparticles. UV irradiation converted the electrostatic interaction intocovalent bonds at the interfaces. These fabricating processes were followed and furtherconfirmed by UV-Vis spectrometry, Fourier transform infrared spectrometer (FTIR),cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Atomicforce microscopy (AFM) shows that these assemblies of colloidal gold nanoparticlesmultilayer films are highly stable and can be kept for a long time, only being removed byphysical scrape. As a biocompatible substrate, the result gold nanoparticles multiplayerfilm can be modified with dopamine, and used for ascorbic acid detection.