| Over the past several years, the three-dimensional ordered construction offunctional molecules on the electrode surfaces has attracted considerable attention,because this kind of multilayer films is the ideal model to study the process ofelectron and mass transfer in the films. Small dye molecules such asphthalocyanines, porphyrins and their related compounds have been extensivelyinvestigated due to their potential applications in the fields of nonlinear optics,photoelectrochemistry, molecular metal, catalysis, sensor, and so on. Theachievement of stable assemblies of such molecules in three-dimensional layeredstructures has become a hot point in recent years.In chapter 2 section 1, highly stable covalently attached multilayer filmscontaining diazoresins (DAR) and iron (Ⅲ) tetrasulfophthalocyanine (FeTsPc)were fabricated by an ionic self-assembly technique and a following photoreactioninduced by UV irradiation. UV irradiation converted the electrostatic interactionat the interfaces into covalent bonds. These changes had been further confirmedby UV-Vis spectra and FTIR spectra. Atomic force microscopy (AFM)experiments showed that the conversion of the interaction at the interfaces hadincreased the stability of the films dramatically. From the surface photovoltagespectra (SPS), it could be followed that the photovoltage response of the n-typesilicon increased by a factor of about 5 times when modified with 6 bilayers ofDAR/FeTsPc multilayer films. The electrode modified with DAR/FeTsPcmultilayer films not only has stable electrochemical behavior but also can catalysethe oxidation of cysteine and the reduction of trichloroacetic acid (TCA). Finally,the diffusion coefficient of TCA was also determined using chronoamperometry.Using weak interaction such as H-bonding attraction as the driving force tofabricate molecular-level layer-by-layer multilayer films was achievedsuccessfully in 1997. One of the advantages of H-bonding self-assemblytechnique is that the formation of the LbL films can be obtained in organicsolvents, which opened a way for preparing multilayer structures using nonionicand water-insoluble polymers. Unfortunately, the attraction of H-bonding is soweak that the fabricated films are easily destroyed. In chapter 2 section 2, wedescribed the fabrication of covalently attached self-assembly multilayer filmsbased on tetra(4-carboxylphenyl)porphyrin (TCPP) and diazoresins (DAR) viaH-bonding attraction and subsequent UV irradiation. First, we fabricated thephotosensitive films from TCPP and DAR via H-bonding attraction between –N2+of DAR and –COOH of TCPP in methanol. Then, the H-bond linkages of theDAR-based films were changed to covalent bonds when undergoing UVirradiation, thus dramatically increasing the films' stability towards polar solvents.The results of UV-Vis absorption showed that the deposition process wasprogressive and uniform. FTIR experiment preliminarily verified the conversionfrom H-bonding to covalent bonds. SPS studies suggested that the TCPP/DARmultilayer films could increase the photovoltage response of n-Si.Recently, research on metal nanoparticles is developed rapidly due to theirsize-dependent optical, magnetic, and catalytic properties, which are differentfrom bulk materials. Silver nanoparticles exhibited superior catalytic activity andimproved enhancement factors for SERS. In chapter 3, we described anothersimple and convenient method for the synthesis of silver nanoparticles, namelythe silver nanoparticles were prepared with mercaptosulfonic acid as the stabilizer,which made the resulting nanoparticles negatively charged in aqueous solution.Then, the silver nanoparticles were used as building blocks to constructself-assembled multilayer films with polycation (PDDA). The fabrication processwas monitored by UV-Vis and the morphology of the multilayer films was studiedby AFM. And the results of CV measurement also confirmed that the silvernanoparticles had successfully assembled into the multilayer films. Finally, thesilver nanoparticles were transferred onto a quartz slide by electrostatic attraction.And the silver nanoparticle films on the quartz slide can serve as SERS-activesubstrates.One of the enduring challenges in electrochemical research is achieving directelectron transfer of proteins or enzymes with electrode. The quest to achieve thisgoal is because direct electron transfer will firstly offer an electrochemical basisfor the investigation of the structure of proteins (enzymes), mechanisms of redoxtransformations of proteins (enzymes), and metabolic process involving redoxtransformations and secondly establish a foundation for fabricating biosensors,catalytic bioreactors, and biomedical devices. Introduction of noble metalnanoparticles to the construction of biosensor is of considerable interest, becausenanoparticles can play an important role in improving the biosensor performancedue to their large specific surface area, excellent biocompatibility andconductivity.In chapter 4, by vapor deposition method, both hemoglobin (Hb) and colloidalsilver nanoparticles (CSNs) were entrapped in a titania sol-gel matrix on thesurface of a glassy carbon electrode (GCE). CSNs could greatly enhance theelectron transfer reactivity of Hb and its catalytic ability toward nitrite. Direct fastelectron transfer between Hb and the GCE was achieved, and a pair ofwell-defined, quasi-reversible redox peaks was observed. The anodic and cathodicpeak potentials are located at –0.298 V and –0.364 V (vs. Ag/AgCl), respectively.The dependence of the formal potential on solution pH indicated that the directelectron transfer reaction of Hb was a one-electron transfer coupled with aone-proton transfer reaction process. Meanwhile, the catalytic ability of Hbtoward the reduction of NO2-was also studied. Accordingly, a NO2-biosensor wasprepared, with a linear range from 0.2 mM to 6.0 mM and a detection limit of 34.0μM. The apparent Michaelis-Menten constant was calculated to be 7.48 mM. Thisnovel method is simple, convenient and versatile. Moreover, the biosensor hadgood long-term stability. In addition, the biosensor also possesses high sensitivityand good chemical and mechanical stability.Extensive research has been done over the last twenty years to study the directelectron transfer of small redox proteins, such as cytochrome c, hemoglobin ormyoglobin. However, direct electron transfer of large redox enzymes has provedto be less successful. Glucose oxidase (GOD) is a homodimer with a molecularweight of about 150-180 kDa containing two tightly bound flavine adeninedinucleotide (FAD) cofactors and catalyzes the electron transfer from glucose tooxygen accompanying the production of gluconic acid and hydrogen peroxide.The most important application of GOD is in biosensors for the quantitativedetermination of glucose in body fluids, foodstuffs, beverages and fermentationliquor. Until now, only a few examples of quasi-reversible voltammograms fordirect electron transfer between the GOD active site and the electrode surface arereported. So developing novel and convenient method to fulfill the direct electrontransfer of GOD has great significance.In chapter 5, the direct electron transfer of GOD was achieved based on theimmobilization of GOD/colloidal gold nanoparticles on a glassy carbon electrodeby a Nafion film. The immobilized GOD displayed a pair of well-defined andnearly reversible redox peaks with a formal potential (E°') of –0.434 V in 0.1 MpH 7.0 phosphate buffer solution and the response showed a surface-controlledelectrode process. The dependence of E°' on solution pH indicated that the directelectron transfer reaction of GOD was a two-electron-transfer coupled with atwo-proton-transfer reaction process. The experimental results also demonstratedthat the immobilized GOD retained its electrocatalytic activity for the oxidation ofglucose. So the enzyme electrode can be used as an amperometric biosensor forthe determination of glucose. In addition, the biosensor also possesses highsensitivity and good chemical and mechanical stability.
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