| Photoelectrochemical bioassay by coupling photoelectrochemical reaction with bio-catalytic reaction is a new emerging technology which has wide applications in the fields of biomedicine and environmental monitoring.The quantitative detection principle is based on the photocurrent variation caused by the direct or indirect reaction between the photogenerated electrons/holes and analytes.Photoelectrochemical bioassay not only possesses the characteristics of electrochemical bioassay,such as economy,sensitivity and portability,but also a low background noise and high sensitivity due to the completely separation of the excitation source and the detection signal.Due to the good specificity,oxidase-based photoelectrochemical bioassay has received comprehensive attention.In typical oxidase-based photoelectrochemical bioassay systems,oxidases can oxidize their substrates in the presence of oxygen,producing a proportional amount of hydrogen peroxide,which can be oxidized by photogenerated holes at the photoanode.Based on the detection principle,a series of high-performance bioassays have been developed.However,conventional bioassay systems have a solid-liquid diphase electrode/electrolyte interface where the oxygen concentration is liquid phase dependent.The significantly low and fluctuating oxygen levels in the liquid phase restrict the kinetics and stability of the oxidase catalytic reaction,limiting the photoelectrochemical bioassay performance.On the other hand,the low charge transport ability and collection efficiency of nanoparticle based photoelectrode restrict the efficiency of photoelectrochemical reaction.The efficiency of the coupled oxidase catalytic and photoelectrochemical reaction affect the performance of oxidase-based photoelectrochemical bioassay including linear detection range,sensitivity and minimum detection limit.In this thesis,we rationally design the reaction interface microenvironment through constructing a solid-liquid-air triphase interface based on superhydrophobic substrate with fast electron transport ability,simultaneously to improve oxidase catalytic reaction and photoelectrochemical reaction kinetics.Relying on the triphase reaction interface,we fabricated several photoelectrochemical bioassay based on hydrogen peroxide oxidation and reduction reaction.Then using glucose as a model analyte to evaluate the performance of fabricated photoelectrochemical bioassay.The main points were summarized as follows:(1)We report the synthesis of one-dimensional single crystal TiO2 nano wire arrays on transparent fluorine-doped tin oxide substrates by a hydrothermal method.Then a photoelectrochemical bioassay system containing a triphase joint interface is constructed by immobilizing oxidases on the top of superhydrophobic TiO2 nanowire arrays.Such triphase reaction systems allow sufficient oxygen to constantly and rapidly transport to the reaction zone from the air phase directly,which greatly enhances and stabilizes the oxidase catalytic reaction,leading to 100-fold wider linear detection range and a higher detection accuracy compared with conventional solid-liquid diphase systems in the detection of glucose.In addition,the one-dimensional single crystal nanowire structure processes rapid photogenerated charge transport ability,which giving the nanowire based triphase system a 32 times lower detection limit and a 13 times higher sensitivity compared with that of a randomly packed nanoparticle based system.The photoelectrochemical bioassay system presents universal applicability.(2)We synthesize one-dimensional single crystal TiO2 nanowire array,and then modified the nanowires with Au nanoparticles by adsorption-reduction method,resulting the formation of Au nanoparticle modified one-dimensional TiO2(Au-TiO2)nanowire arrays.A visible light responsive photoelectrochemical bioassay system is constructed with a triphase photoanode that fabricated by immobilizing glucose oxidase on superhydrophobic Au-TiO2.Au nanoparticles can absorb visible light with its surface plasmon resonance effect to generate holes to react with oxidase catalytic reaction product hydrogen peroxide;the unique architecture of the photoanode enables fast electron transport and convenient oxygen accessibility,resulting in excellent analytical performance of the visible light responsive photoelectrochemical bioassay system with wide linear detection range,low detection limit,high sensitivity and stability.(3)We develop a novel photoelectrochemical bioassay system upon cathodic measurement of enzymatic product hydrogen peroxide.The system contains a TiO2 nanowire photoanode and a bio-cathode with a solid-liquid-air triphase interface constructed by assembling an oxidase layer on the surface of superhydrophobic single crystal TiO2 nanowire arrays.One-dimensional TiO2 nanowire photoanode can effectively absorb the incident light,the resulting photogenerated electrons can spontaneously transfer to the bio-cathode and participate in the reduction reaction of hydrogen peroxide.The solid-liquid-gas triphase bio-cathode can enable oxygen rapidly diffusing from the air phase to the bioassay reaction zone,leading to the interface oxygen concentration and background photocurrent keeping constant,offering a unique opportunity for accurately measuring hydrogen peroxide by photoelectrochemical reduction method.The cathodic measurement enables PEC bioassay system exhibiting remarkably high detection selectivity,and compared with a normal diphase solid-liquid photoelectrochemical bioassay system a 100-fold extended linear detection range.The rapid electron transport in the single crystal TiO2 nanowire arrays endows the bioassay system an 845-fold enhanced sensitivity,and three orders of magnitude lower minimum detection limit compared with TiO2 nanoparticle based ones.The detection principle is general and thus applicable for quantification of other bio-species.In addition,the bioassay can proceed without external bias,a behavior ideally suited for wearable and implanted electronic devices. |
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