Synthesis And Self-assembly Of Functionalized Graphene Quantum Dots And Their Applications In Bioanalysis

Graphene Quantum Dots(GQDs)as multifunctional fluorescent probes and labeling platforms have been at the center of researches in a wide range of fields such as materials science,bioimaging,and analytical chemistry.This is mainly due to their excellent light stability and biocompatibility.GQDs which are prepared from graphene oxide have oxygen-rich surface functional groups,such as hydroxyl and carboxyl groups,providing a pathway for further modification.In addition to their extraordinary photoluminescence properties,GQDs also show great potential in photocatalysis and enzyme mimics,which have been successfully achieved in electrochemical and colorimetric sensors.The greatest advantage of GQDs is its tunable optical properties.In other words,the fluorescence of GQDs is mainly affected by their characteristics and solution conditions,such as the size of nanodots,edge modification,functional groups,surface potential and passivation,p H,and solvent.GQD is the most promising candidate for the development of novel fluorescent probes,which has great potential in chemical sensors and bioimaging.Chapter 1.OverviewThis chapter mianly introduces the development of graphene quantum dots since its introduction last decade.Then,the characterization methods of graphene quantum dots,such as transmission electron microscopy,atomic force microscopy and X-ray photoelectron spectroscopy,are summarized.As a carbon-based nanomaterials with low toxicity,ease to modification and good fluorescent properties,graphene quantum dots are widely used in fluorescence sensing and cell imaging,electrochemical and electrochemiluminescence sensors,photovoltaic materials,and enzyme-like catalysis.This chapter gives an example of the representative results of graphene quantum dots in various fields of applications in recent years,and gives an outlook on the future development.Chapter 2.A Novel Ratiometric Probe Based on Self-catalytic Modulation of Fluoresence of Graphene Quantum DotsRatiometric fluorescence probes are very important in research because they can provide built-in corrections to the environment to reduce background interference.However,conventional ratiometric fluorescent probes usually require two different luminescent materials.This article reports a new type of ratiometric probe based on single-wavelength-emitting materials.The probe works through a self-catalyzed mechanism by modulating the luminescence properties of the graphene quantum dots.The ratiometric sensor shows high sensitivity and specificity for iron ions.In addition,this sensor was successfully used to monitor ferritin levels in Sprague Dawley rats that were with chemically induced acute liver injury.The proposed single wavelength ratio fluorescent probes may greatly expand the applicability of ratiometric sensors in diagnostic equipment,medical applications,and analytical chemistry.Chapter 3.Boronic Acid Functionalized Graphene Quantum Dots for Selective and Sensitive Glucose Determination in Rats3-Aminobenzeneboronic acid functionalized graphene quantum dots(APBA-GQDs)were synthesized and used as a selective and sensitive sensing system for glucose.We studied the working mechanism for the selective recognition of glucose over other sugars of our fluorescent assay.Combined with microdialysis,glucose was monitored successfully in vivo in the brain of rat.Chapter 4.Self-assemblies of Graphene Quantum DotsThis chapter mainly contains two parts.In the first part we constructed the coordination assemblies of graphene quantum dots.We use different metal ions to coordinate with oxygen-rich functional groups such as carboxyl groups around the graphene quantum dots,thereby inducing the assembly of graphene quantum dots into nanochains,nanospheres,nanoshell structures,and even star-shaped structures.We studied in detail the effects of different assembly conditions of graphene quantum dots on the morphology,and detailed structure and spectroscopic characterization of the graphene quantum dots assembled nanochains.In the second part,we discussed the layer-by-layer assemblies of graphene quantum dots/graphene oxide and cytochrome c.We have conducted a detailed study of the structures and the formation process of the layer-by-layer assembly.It is found that the composite material has excellent peroxidase activity,and the enzyme activity is highly stable and easy to recycle.We then successfully expanded the composite to a colorimetric sensor that detects carcinogenic aromatic amines.The colorimetric sensor has excellent selectivity and sensitivity to carcinogenic aromatic amines such as naphthylamine and is very suitable for rapid on-site testing of garment leather samples.Chapter 5.Theoretical Studies of Graphene Quantum DotsIn this chapter,we studied the properties and mechanism of graphene quantum dot assemblies and low-dimensional carbon-based nanostructures by the use of molecular modeling and computational chemistry tools,such as density functional theory calculations and molecular dynamics simulations.The main contents are as follows:(1)Model of graphene quantum dot assemblies.From the theoretical view,we studied the variaty of the morphology of graphene quantum dots assmblies and the mechanism of their Raman scattering enhancement.(2)Layer-by-layer graphene/cytochrome c composites model.We used molecular dynamics simulations to study the mechanism of peroxidase activity enhancement in graphene oxide/cytochrome c composites,and further investigated the inhibition mechanism of aromatic amines in the composites.(3)Carbon nanotube-graphene nanoribbon heterojunction model.We used density functional theory to calculate the stability,electronic,and magnetic properties of carbon nanotube-graphene nanoribbon heterojunctions.The correlation between these physical properties and the structural parameters of the heterojunction were further studied.