Electrochemical Synthesis Of Fluorescent Carbon Nanodots And Its Applications In Biochemical Analysis

As a new fluorescent carbon nanomaterial, carbon nanodots(C-dots) exhibit excellent properties such as unique optical property, good biocompatibility and chemical stability, strong resistance to photobleaching and photodegradation, and low toxicity. Intensive efforts have been focused on the application of C-dots in biomedicine, biosensing and catalysis. However, improvements are needed in synthesis of C-dots due to complicated operation, extreme condition and high cost of the existed methods. Meanwhile, the excellent properties of C-dots are not adequately applied. Hence, to develop new synthesis methods and to explore the new applications of C-dots are meaningful. Electrochemical methods for preparation of nanomaterials are known for the controllability, environment-friendly, low-cost and facility. In this dissertation, different novel electrochemical methods were proposed to prepare C-dots with different properties. And based on the as-prepared C-dots, a couple of sensors for some biomolecules were constructed.1. A facile electrochemical method for C-dots was introduced. In the mixture of Na OH/water, monodisperse C-dots were obtained from graphite rod through an electrochemical oxidation. Transmission(TEM), selected area electron diffraction(SAED), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) were used to characterize the internal structure and surface status. The role of Na OH in synthesis was investigated. Hydroxyl and oxygen radicals were generated during the process and they are important for generation of C-dots. Appropriate amount of Na OH could make the synthesis more efficient. This study is meaningful for invesitigation of electrochemical synthesis of nanomaterials.2. A novel electrochemical synthesis for graphene quantum dots(GQD) with large scale from graphite oxide(GO) in pure water has been proposed. Unlike traditional electrochemical method using graphite-based materials as the electrodes, two Pt sheets were used as the anode and cathode here. GO aqeoussolution as reactant without any other chemical reagent. GQDs with different sizes and different emission properies were obtained with the yield of 65.5% in weight. Moreover, the resultant GQDs possess excellent peroxidase-like activity for the reduction of hydrogen peroxide, which were applied in the glucose detection successfully. This method is simple, easily controllable and readily scalable to industrial levels.3. A facile and general strategy using electrochemical carbonization of low-molecular weight organic compounds was proposed. As precursors, the organic molecules transformed into carbon-containing particles after being electrochemical carbonization in a basic condition. The resultant C-dots exhibited excellent excitation-dependent and size-dependent fluorescence without complicated purification and passivation. The size of as-prepared C-dots can be adjusted by the synthesization potential. C-dots of high quality were prepared from different small molecular alcohols successfully, suggesting that the research provides a new methods for preparation of fluorescent C-dots with high universality. In addition, the luminescence microscopy of the C-dots in human cancer cells is demonstrated, the results indicate that as-prepared C-dots are low-toxicity and can be used in imaging application. This method is simple and economical, and may give a new sight to synthesis of C-dots.4. N-doped carbon nanodots(NC-dots) with excellent fluorescence were synthesized through an electrochemical carbonization of ethanolamine. A novel nanosensor was developed to discriminate cysteine(Cys) from glutathione(GSH) and homocysteine(Hcy) with dual signals: colorimetric and photoluminescence(PL). The nanosensor(NC-dots/Au NPs) was constructed by NC-dots and Au nanoparticles(Au NPs) through assembling NC-dots “shell” on Au NPs and showed the obvious different response to Cys, Hcy and GSH with colorimetric and PL signals. The discrimination effect for Cys is originated from conformations and interaction difference of the thiols groups in Cys and Hcy and/or GSH with Au NPs. Among them, only Cys can quickly penetrate into the NC-dots “shell” of the composite and induce the dispersing of the aggregatedNC-dots/Au NPs, which led to the color change from purple to red and the recovery of PL of NC-dots. This assay was successfully applied for the detection of Cys in human serum with the detection limit of 4 n M. This study provides a simple, rapid and selective sensor for Cys with dual signals, which would widen the application of C-dots in biosensers.5. N-doped carbon nanodots(NC-dots) with excellent PL were prepared through an electrochemical carbonization of glycol and ethanediamine. In the presence of Fe2+, the PL intensity decreased apparently when H2O2 was added. H2O2 could react with Fe2+ to yield the hydroxyl radical(·OH) in acidic condtidion, which is called as the Fenton reaction. Hence, it is possible that the resultant ·OH can cause the quenching of NC-dots. Then, a simple biosensor for glucose was established based on NC-dots, which exhibited excellent sensitivity and selectivity. This study is important for constructing biosensors based on C-dots.