Assembly Of Porphyrin-gold Nanoparticles And Electrochemical Biosensing

Porphyrins as the mimics of many important enzymes are an important class of organic molecules in nature. Especially, metalloporphyrins, which have the high catalytic activities, are orderly assembled onto many nanomaterials with well-defined shapes and sizes to mimic metalloprotein enzymes and realize their functions. Indeed, metalloporphyrins are excellent electron transfer mediators and exhibit good electrocatalytic activity toward the reduction or oxidation of many biomolecules related to life process. Moreover, metalloporphyrins can interact with DNA functionalized nanomaterials for preparation of detection probe, which leads to the enhanced current and realizes their signal amplification. Thus based on the bionic catalysis of porphyrins, the nanocomposites of metalloporphyrin-nanomaterials can be employed to design the novel detection probe and electrochemical biosensor. This thesis focuses on the preparation of detection probe and the application of porphyrin-gold nanoparticle nanocomposite in electrochemical biosensing.1. Porphyrin-functionalized gold nanoparticles for selective electrochemical detection of peroxyacetic acidTwo layers of cationic iron(III) meso-tetrakis (N-methylpyridinum-4-yl)porphyrin (FeTMPyP) and anionic gold nanoparticles (GNPs) were alternately assembled on a poly(diallyldimethylammonium chloride)-wrapped carbon nanotube (PDDA-CNT)-modified electrode via electrostatic interactions. The porphyrin-functionalized gold nanoparticles were characterized by scanning electron microscopy and UV-vis absorption spectrometry. The (FeTMPyP-GNP)2/PDDA-CNT modified electrode showed two stable and well-defined peaks at-0.112V and-0.154V, which were attributed to the GNP-accelerated redox process of Fe(III)TMPyP/Fe(II)TMPyP. The modified electrode possessed excellent electrocatalytic behavior for the reduction of peroxyacetic acid (PAA). The resulting biosensor exhibited a fast amperometric response to PAA (-3s), with a wide linear range from2.5×10-6M to1.1×10-3M and a detection limit of0.50μM at a signal-to-noise ratio of3. More importantly, H2O2did not interfere with the detection. Thus, this biosensor enabled highly sensitive detection of PAA without removing H2O2and showed a promising potential in practical applications.2. Bionic catalysis of porphyrin for electrochemical detection of DNAA novel electrochemical strategy was designed for the detection of DNA based on the bionic catalysis of porphyrin. The detection probe was prepared via the assembly of thiolated double strand DNA (dsDNA) with gold nanoparticles (GNPs), and then interacted with cationic iron (III) meso-tetrakis (N-methylphyridinum-4-yl) porphyrin (FeTMPyP) via groove binding along the dsDNA surface. The resulting nanocomplex was characterized with transmission electron microscopy, UV-vis absorption and circular dichroism spectroscopy. The FeTMPyP-DNA-GNPs probe on gold electrode demonstrated the excellent electrocatalytic behaviors toward the reduction of O2, since both GNPs and DNA accelerated the electron transfer between FeTMPyP and the electrode, and increased the amount of adsorbed FeTMPyP. Based on the bionic catalysis of porphyrin for the reduction of O2, the resulting biosensor exhibited a good performance for the detection of DNA with a wide linear range from1.0pM to10nM and detection limit of0.25pM at the signal/noise of3. More importantly, the biosensor presented excellent ability to discriminate the perfectly complementary target and the mismatched stand. This strategy could be conveniently extended for detection of other biomolecules. To the best of our knowledge, this is the first application of bionic catalysis of porphyrin as detection probe and opens new opportunities for sensitive detection of biorecognition events.