Nanoassembly Of Porphyrin And Its Biosensing

Porphyrins are important classes of conjugated organic molecules, which could mimic the active site of many important enzymes. A series of porphyrin molecules, such as planar porphyrin, picket-fence porphyrin, macroporphyrin and triphyrin, have been synthesized to mimic the catalytic activity of biological protein. The order nanoassembly of porphyrins on nanomaterials by covalent or noncovalent way can mimic metalloprotein enzymes and realize their functions. Metalloporphyrins have been well used as electron transfer mediators and exhibited good electrocatalytic activity toward the reduction or oxidation of many small molecules related to life process. Thus, the nanocomposites of metalloporphyrin-nanomaterials have been good candidates to construct novel electrochemical biosensors. Meanwhile, owing to the good photophysical and photochemical properties, the nanocomposites of metalloporphyrin-nanomaterials have also been employed to develop novel photochemical and photoelectrochemical biosensing platforms for detection of biomolecules. This thesis focuses on nanoassembly of porphyrins, and biosensing application of the as-prepared nanocomposite.1. Noncovalent nanoassembly of porphyrin on single-walled carbon nanotubes for electrocatalytic reduction of nitric oxide and oxygenWater-soluble iron(Ⅲ) meso-tetrakis(N-methylpyridinum-4-yl)porphyrin (FeTMPyP) was successfully immobilized on single-walled carbon nanotubes (SWNTs) via 1-pyrenebutyric acid (PBA). The formed SWNTs/PBA/FeTMPyP film showed an enhanced electrocatalytic peak at -0.70 V and -0.17 V towards reduction of nitric oxide and oxygen, respectively. SWNTs accelerated the electron transfer between FeTMPyP and electrode, and increased the amount of FeTMPyP adsorbed. FeTMPyP acted as a catalyst to decrease the reduction potential, exhibiting a synergy in electrocatalysis. The excellent electrocatalytic behaviors made SWNTs/porphyrin nanocomposite have a promising potential in fabricating new type of biosensors.2. Functionalization of carbon nanotubes with water-insoluble porphyrin in ionic liquid:direct electrochemistry and highly sensitive amperometric biosensing for trichloroacetic acidA functional composite of SWNTs with hematin, a water-insoluble porphyrin, was first prepared in 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF6]) ionic liquid. The novel composite in ionic liquid was characterized by scanning electron microscopy, ultraviolet absorption spectroscopy, and electrochemical impedance spectroscopy, and showed a pair of direct redox peaks of the FeⅢ/FeⅡcouple. The composite-[BMIM][PF6] modified glassy carbon electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid (TCA) in neutral media due to the synergic effect among SWNTs, [BMIM][PF6], and porphyrin, which led to a highly sensitive and stable amperometric biosensor for TCA with a linear range from 9.0×10-7 to 1.4×10-4 M. The detection limit was 3.8×10-7 M at a signal-to-noise ratio of 3. The TCA biosensor had good analytical performance, such as rapid response, good reproducibility, and acceptable accuracy, and could be successfully used for the detection of residual TCA in polluted water. The functional composite in ionic liquid provides a facile way to not only obtain the direct electrochemistry of water-insoluble porphyrin, but also construct novel biosensors for monitoring analytes in real environmental samples.3. Noncovalent assembly of picket-fence porphyrin on nitrogen-doped carbon nanotubes for highly efficient catalysis and biosensingWater-insoluble picket-fence porphyrin was first assembled on nitrogen-doped multiwalled carbon nanotubes (CNx-MWNTs) via the Fe-N coordination for highly efficient catalysis and biosensing. Scanning electron micrographs, Raman spectra, X-ray photoelectron spectrum, ultraviolet-visible absorption spectra, and electrochemical impedance spectra were employed to characterize this novel nanocomposite. The presence of CNx-MWNTs led to the direct electrochemistry of porphyrin to form high-valent Fe(IV) porphyrin at low potential in neutral aqueous solution, which produced excellent catalytic activity toward the oxidation of sulfite. Using sulfite that has been widely used as a versatile additive and preservative in the food and beverage as a model, a highly sensitive amperometric biosensor for sulfite was proposed. The biosensor showed a linear range of 4 orders of magnitude from 8.0×10-7 to 4.9×10-3 mol L-1 and a detection limit of 3.5×10-7 mol L-1 due to the highly efficient catalysis of the nanocomposite. The designed platform and method had good analytical performance and could be successfully applied in the determination of sulfite in beverage. The direct noncovalent assembly of porphyrin on CNx-MWNTs provided a facile way to design novel biofunctional materials for biosensing and photovoltaic devices.4. Characterization, direct electrochemistry and amperometric biosensing of graphene by noncovalent functionalization with picket-fence porphyrinReduced graphene oxide (RGO) was prepared and functionalized with picket-fence porphyrin,5,10,15,20-tetrakis [aaaa-2-trismethylammoniomethyl-phenyl] porphyrin iron(Ⅲ) pentachloride (FeTMAPP), viaπ-πinteractions. The resulting nanocomposite was characterized by atomic force microscopy, transmission electron microscopy, contact angle measurements, fluorescence and Raman, ultraviolet-visible absorption spectroscopy. Attributing to the introduction of positively-charged FeTMAPP, the functionalized RGO showed good dispersion in aqueous solution. The RGO could greatly accelerate the electron transfer of FeTMAPP to produce a well-defined redox couple of FeⅢ/FeⅡat -0.291 and -0.314 V. Due to the synergic effect between RGO and porphyrin, the nanocomposite showed excellent electrocatalytic activity toward the reduction of chlorite, leading to highly sensitive amperometric biosensing at low applied potential. The biosensor for chlorite showed a linear range from 5.0×10-8 to 1.2x10-4 mol L-1 with a detection limit of 2.4×10-8 mol L-1 at a signal to noise of 3. The picket-fence porphyrin could serve as an efficient species to functionalize graphene for electronic and optical applications.5. Sandwich nanohybrid of single-walled carbon nanohorns-TiO2-porphyrin for electrocatalysis and amperometric biosensing toward chloramphenicolA sandwich nanohybrid of single-walled canbon nanohorn-TiO2-porphyrin was prepared via the dentate binding of TiO2 nanoparticles to the carboxylate groups. Transmission electron microscopy, Raman, X-ray photoelectron, infrared spectroscopy and electrochemical impedance spectra were employed to characterize this novel nanohybrid. The direct electrochemistry corresponding to the redox couple of FeⅢ/FeⅡof porphyrin is realized. The SWNHs-TiO2-porphyrin modified electrode shows excellent electrocatalytic activity toward reduction of chloramphenicol (CAP) at -0.56 V in neutral media due to the synergic effect among SWNHs, TiO2 and porphyrin. The electroactive site of CAP is confirmed to be nitroaromatic group. Under optimal conditions, the proposed amperometric biosensor could detect CAP with analytical performance. The linear detection range could be up to 136μM with a detection limit of 0.9 nM at the signal to noise ratio of 3. The biosensor could be successfully used for detection of CAP in CAP injection without any need of sample pretreatment except an appropriate dilution of sample. The sandwich nanostructure of SWNHs-TiO2-porphyrin can be extended for the application in the photovoltaic- and photo-catalysis in solar cells.6. Low-potential photoelectrochemical biosensing using porphyrin-functionalized TiO2 nanoparticlesA novel photoelectrochemical biosensing platform for the detection of biomolecules at relatively low applied potentials was constructed using porphyrin-functionalized TiO2 nanoparticles. The functional TiO2 nanoparticles were prepared by dentate binding of TiO2 with sulfonic groups of water-soluble [meso-tetrakis(4-sulfonatophenyl)porphyrin] iron(III) monochloride (FeTPPS) and characterized by transmission electron microscopy; contact angle measurement; and Raman, X-ray photoelectron, and ultraviolet-visible absorption spectroscopies. The functional nanoparticles showed good dispersion in water and on indium tin oxide (ITO) surface. The resulting FeTPPS-TiO2-modified ITO electrode showed a photocurrent response at +0.2 V to a light excitation at 380 nm, which could be further sensitized through an oxidation process of biomolecules by the hole-injected FeTPPS. Using glutathione as a model, a methodology for sensitive photoelectrochemical biosensing at low potential was thus developed. Under optimal conditions, the proposed photoelectrochemical method could detect glutathione ranging from 0.05 to 2.4 mmol L-1 with a detection limit of 0.03 mmol L-1 at a signal-to-noise ratio of 3. The photoelectrochemical biosensor had an excellent specificity against anticancer drugs and could be successfully applied to the detection of reduced glutathione in gluthion injection, showing a promising application in photoelectrochemical biosensing.7. Photoelectrochemistry of free-Base porphyrin functionalized zinc oxide nanoparticles and its biosensing applicationThe photoelectrochemical properties of free-base porphyrin functionalized zinc oxide nanoparticles was studied. A universal photoelectrochemical biosensing platform was constructed on ITO using the functional nanohybrid. The nanohybrid was synthesized via dentate binding of ZnO nanoparticles with carboxylic groups of 4,4',4",4'''-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis (benzoic acid) (TCPP), and characterized with scanning electron microscopy, contact angle measurement, and spectral techniques. The nanohybrid coated ITO electrode showed an efficient photocurrent response under irradiation at the wavelength of 360 nm, which could be greatly improved upon addition of cysteine by its oxidation at +0.3 V. The possible mechanism was that cysteine acts as a sacrificial electron donor to scavenge the photogenerated holes locating on excited state of TCPP that then injects photoexcitation electrons into the conduction band of ZnO nanoparticles, leading to photoinduced electrons to the ITO electrode. Based on this enhanced photocurrent signal, a novel method for photoelectrochemical detection of cysteine was developed with a linear range of 0.6 to 157μmol L-1 in physiological media. The detection limit was 0.2μmol L-1 at a signal to noise ratio of 3. The novel strategy of cysteine analysis would provide an alternative method for monitoring of biomolecules and extend the application of porphyrin functional semiconductor nanoparticles.8. Photoelectrochemical immunosensing based on a nanocomposite of graphene-quantum dots using chemiluminescence reaction as light sourceReduced graphene oxide-CdS nanocomposite was prepared by a one-pot reaction. A dispersion of graphene oxide (GO) in an aqueous solution of Cd2+ was reacted with H2S gas, which acts as a sulphide source as well as a reducing agent, resulting in the formation of CdS quantum dots and simultaneous reduction of graphene oxide to RGO. Fluorescence, infrared spectra, Raman spectroscopy and electrochemical impedance spectra were employed to characterize this resulting nanocomposite and confirmed that GO has been simultaneously reduced to RGO during the deposition of CdS quantum dots. The surface related defect fluorescence emission shown of free CdS quantum dots are quenched in the nanocomposites after the interaction of the surface of the CdS quantum dots with RGO. On the other hand, luminol functional ized gold nanoparticles (AuNPs)-labeled (HRP) and (antibody)Ab was synthesized as detecting probe. Uminol-H2O2-horseradish peroxidase (HRP)-4-Iodophenol(PIP) was selected as a chemiluminescence system, which can produce appropriate exciting light excite and excite RGO-CdS nanocomposite. Using such specific interaction between antigen and antibody, a photoelectrochemical immunosening platform with chemiluminescence reaction as light source was constructed for detection of carcinoembryonic antigen (CEA). The proposed photoelectrochemical method could detect CEA ranging from 0.05 to 20 ng mL-1 with a detection limit of 0.01 ng mL-1 at a S/N ratio of 3. Using chemiluminescence reaction as light source extends the application of photoelectrochemical biosensor, especially for in situ or online monitoring.