石墨烯量子点的制备及在生物传感器中的应用研究进展

A Survey on the Synthesis and Application in Sensors of Graphene Quantum Dots

石墨烯是由一层碳原子以sp^2杂化轨道按蜂巢晶格排列构成的二维碳纳米材料,由于其超大的平面共轭结构,石墨烯中的π电子具有显著的离域效应。石墨烯具有许多令人惊奇的电子或电学性质,比如室温量子霍尔效应、自选传输性质、极高的载流子迁移率和超低的电阻率以及优异的光学性质和力学性质。然而,与其他绝大多数二维材料不同,较大二维尺寸的石墨烯还具有零带隙的半金属材料特性,限制了石墨烯在光电器件和半导体等领域的应用。因此,如何打开石墨烯的带隙,将其从半金属材料转变为半导体材料,引起了人们的广泛兴趣。目前,已知打开石墨烯带隙的方法主要有两种:一种是对石墨烯进行化学掺杂以破坏其π电子共轭体系;另外一种是基于量子效应,将石墨烯切割成纳米带、纳米筛或量子点。石墨烯量子点(GQDs)是二维平面尺寸小于100 nm的石墨烯片段,因其具有量子限域效应和边界效应而呈现出特殊的物理化学性质,是一种具有带隙的半导体材料。与传统半导体量子点相比,GQDs具有毒性低、水溶性好、化学活性低、生物相容性好以及荧光性质稳定等突出优点。此外,GQDs具有单原子层平面共轭结构和较大的比表面积,同时表面的含氧基团可以为外来分子与之结合提供活性位点,在太阳能电池、光电子器件、生物医药等领域具有广泛的应用前景。GQDs的制备方法主要分为自上而下和自下而上两种方法。自上而下法主要包括强酸氧化法,水热/溶剂热法,电化学氧化法等。该方法的优点是原料来源丰富、制备过程相对简单,制备所得的GQDs表面含有丰富的含氧基团,具有良好的水溶性,易于表面功能化。自下而上方法主要分为可控有机合成和碳化反应。前者可以制备出具有精确碳原子数、大小和形状均一的GQDs,但是制备过程复杂繁琐、反应耗时长且产率较低,而后者所制备的GQDs,其尺寸和结构难以控制,产物具有多分散性。本文全面介绍了石墨烯量子点的各种制备方法,对这些方法的特点进行了评论,同时对重要或新颖方法的反应机理进行了阐述,并且重点介绍了GQDs在生物传感器方面的应用,最后对GQDs的未来研究和发展前景进行了展望。

Graphene belongs to two dimension carbon nanomaterial composed of a layer of carbon atoms arranged in sp^2 hybrid orbitals with honeycomb lattice.Theπelectrons in graphene exhibit notable delocalization effect doe to its large planar conjugate structure.Graphene shows many amazing electronic or electrical properties,such as room temperature quantum hall effect,free transport properties,high carrier mobility,low resistivity,excellent optical properties and mechanical properties.Unfortunately,different from most other two-dimensional materials,the graphene of large size bears zero band gap and semi-metallic property,which hinders its application in the fields of photoelectric device,semiconductor and so forth.Accordingly,how to open the band gap of graphene and transform it from semi-metallic material to semiconductor material has aroused nume-rous interests.Currently,there are two known approaches to open the band gap of graphene.One is to to break theπelectronic conjugate system of graphene by chemical doping.The other is to tailor graphene into nanorods,nanosieves,or quantum dots based on their quantum effects.Graphene quantum dots(GQDs)are segments of two-dimensional graphene with plane size less than 100 nm.Thanks to the quantum confined effect and boundary effect,GQDs are endowed with special physical and chemical properties,and they are also semiconductor materials with band gap.GQDs are superior to conventional semiconductor quantum dots,owing to their low toxicity,favorable water solubility,low chemical activity,satisfactory biocompatibility and stable fluorescence properties.Besides,GQDs possess monatomic planar conjugate structure and large specific surface area,and the oxygen groups on the GQDs surface can provide active site for the binding of foreign molecules.Consequently,GQDs show a broad prospect of application in solar cells,optoelectronic devices,biological medicine and other fields.The synthesis approaches of GQDs can be divided into top-down and bottom-up methods.The top-down method mainly includes strong acid oxidation,hydrothermal/solvothermal reactions,electrochemical oxidation,and so forth,which feature good water solubility and is prone to be functionalized.The bottom-up method is mainly divided into controllable organic synthesis and carbonization reaction.As for the former,GQDs with uniform size and shape,and precise carbon atom number can be obtained,but it suffers from complicated synthtic process,long reaction time and low production rate.While the latter is the common reaction for the synthesis of GQDs,although the size and structure of the products can be hardly to control,and the obtained GQDs usually present polydispersity.This paper comprehensively introduces the diverse synthesis approaches of GQDs,and provide detailed comments on these approaches.At the same time,the reaction mechanism of important or novel methods are expounded.In addition,emphasis is put on the applications of GQDs in the field of biosensors.Finally,the research and development of the GQDs in the future is proposed.