Research Of Optical Sensors Based On Graphene And Its Nanocomposites

Graphene, a novel two-dimension material consist of sp2-hybridized carbon atoms, exhibits high specific surface area, excellent electron transfer ability, superlative mechanical strength, high transparency, and high thermal conductivity. Thanks to these extraordinary and superior properties, graphene has already revealed a great number of potential applications with possible uses in fields of energy, environment, medical, sensors etc. Especially, in the chemical analytical area, graphene perfectly meets the requirements for designing sensors with high sensitivity. Graphene oxide could act as peroxidase mimics; graphene could quench the fluorescent moieties due to fluorescence resonance energy transfer; moreover, graphene is promising material for surface-enhanced Raman scattering （SERS）. These specific and intrinsic optical properties of graphene contributes to widely applications in photochemical sensors. The development of optical sensors for the detection of heavy metal ions and sugars with easy operation, fast response, high sensitivity and selectivity, is highly desirable in many areas, including environmental protection and disease prevention.In this dissertation, we aim to develop optical sensors with excellent performance for the detection of heavy metal ions and sugars based on the extraordinary properties of functional graphene nanocomposites. The dissertation includes five chapters:Chapter 1. OverviewThis chapter gives the outlines and reviews of structure, property, synthesis, functional methods, and applications of graphene. Finally, the purpose and significance of our work are indicated.Chapter 2. A label-free SERS Sensor for Pb²⁺ detection Based on Graphene/gold nanoparticles/cucurbit[7]urilIn this work, we develop a novel surface-enhanced Raman scattering （SERS）-based sensor for the selective trace analysis of Pb²⁺. The SERS-based sensor is assembled from gold nanoparticles （AuNPs） and graphene using cucurbit[7]uril （CB[7]） as a precise molecular glue and a local SERS reporter. Upon the addition of Pb²⁺, CB[7]s form stronger complexes with Pb²⁺and desorb from AuNPs, resulting in a sensitive "turn-off" of SERS signals. This SERS-based assay shows a limit of detection （LOD） of 0.3 nM and a linear detection range from 1 nM to 0.3 μM for Pb²⁺.Chapter 3. A Sensitive Pb²⁺ Probe Based on the FRET of Graphene Oxide and Enhancement Leaching of Gold NanoparticlesIn this work, fluorescence reporter AP was grafted on AuNPs through Au-N bond. In presence of GO, the system shows fluorescence quenching because of fluorescence resonance energy transfer （FRET） through π-π stacking between AP and GO. With the addition of Pb²⁺ and S2O32-, the system displays fluorescence recovery, which is attributed to the fact that Pb²⁺ could accelerate the leaching of the AuNPs from GO surfaces and releasing of AP into aqueous solution. Under the optimal condition, the fluorescence Pb²⁺ sensor shows a linear range of 1 nM to 0.2 μM with a detection limit of 0.6 nM.Chapter 4. A Label-free Colorimetric Sensor for Pb²⁺ Detection Based on the Acceleration of Gold Leaching by Graphene OxideIn this work, we developed a novel, label-free, colorimetric sensor for Pb²⁺ detection based on the acceleration of gold leaching by graphene oxide （GO） at room temperature. Gold nanoparticles （AuNPs） can be dissolved in thiosulfate （S2O32-） aqueous environment in the presence of oxygen, however, the leaching rate is very slow due to the high activation energy （27.99 kJ/mol）. In order to enhance the reaction, some accelerators should be added. Compared with the traditional accelerators （metal ions or middle ligands）, we found that GO could efficiently accelerate the gold leaching reaction. Kinetic data demonstrate that the dissolution rate of gold in the Pb²⁺-S2O32--GO system is 5 times faster than that without GO at room temperature. In addition, the effects of surface modification and the nanoparticle size on the gold etching were investigated. Based on GO-accelerated concentration-dependent colour changes of AuNPs, a colorimetric sensor for the Pb²⁺ detection was developed with a linear range from 0.1 to 20 μM and the limit of detection （LOD） was evaluated to be 0.05 μM.Chapter 5. Research of Sugar Sensor Based on the Mimic Peroxidase Ability of Graphene/ABAGraphene oxide（GO） displays well mimic peroxidase ability, which is usually evaluated through the oxidation of TMB by H2O2. This work studies the influence of the mimic enzyme ability of GO by aromatic compounds with different numbers of benzene rings and substituent groups. As a result, the π-π interaction is found to well inhibit the catalytic efficiency of GO, with an inhibit effect enhanced by the numbers of benzene rings. In addition, aromatic amine compounds shows extremely inhibit effect due to the active lone pair electrons. According to this phenomena, we develop a fructose sensor based on the 3-amino phenyl boronic acid（ABA） and GO. This sensor show displays a detection limit of 0.08 mM with a linear detection range from 0.2 mM to 15 mM.