Research On Opto-mechanical And Opto-thermal Properties Of Carbon Nanocoils And Their Applications As Flexible Probes

Due to their excellent physical properties,chemical properties and biocompatibility,carbon nanomaterials have attracted great attentions.Carbon nanomaterials have many different morphologies,among which carbon nanocoils(CNCs)are famous for their unique three-dimensional helical morphology on nanoscale.The spiral structure of CNCs makes them different from other carbon nanomaterials,not only in their unique conductive property and thermal property,but also in their axial tensile property and large specific surface area.Therefore,CNCs are expected to have great potential applications in the fields of micro/nano electromechanical systems,highly sensitive strain sensing,near-infrared absorption and utilization,etc.At present,the mechanical and electrical properties as well as the related applications of CNCs have arose intensive studies.However,there are few studies on the optical property of CNCs,and practical application research is still in the early stage.In this thesis,the opto-mechanical behavior and photothermal conversion performance of CNCs under laser irradiation are emphatically explored,which not only enrich the understanding to the physical properties of CNCs,but also build a good foundation for the potential applications of CNCs in micro/nano opto-mechanical and mechano-electrical systems.In addition,based on the excellent mechanical property and biocompatibility,the applications of CNCs as flexible probes,on micro/nano force sensors and bioprobes,are preliminarily explored.The main contents are as follows:Firstly,the opto-mechanical effect of laser on a single CNC cantilever is studied.The optical force on CNC is repulsive,which is calculated to be on the order of pico-newton.Then the continuous laser signal is modulated by a chopper to periodic square wave signal,so the variation of laser intensity results in the change of the optical force,which leads to the stable vibration of the CNC cantilever.We have studied the vibration characteristics of the CNC cantilever experimentally,and described the vibration theoretically based on the continuum medium model and Fourier Transform.The theoretical deductions fit well with the experimental results,and the resonance frequency and damping factor of the CNC cantilever are obtained directly.Secondly,we explore the photo-thermal conversion performance and surface heat transfer ability of CNCs.Under the NIR-laser irradiation on a single CNC,a high-speed living cell ejection is realized in a yeast cell solution.The ejection reveals a thermal convection induced by the photo-to-thermal effect of CNC.The dynamic photo-thermal conversion process of CNC is investigated by finite element analysis method.It is found that the maximum velocity of the thermal convection reaches more than 1 100 um/s.Combining the experimental results with the analytical results,the photo-thermal conversion efficiency of CNC is calculated to be 60%,which is higher than those of other usual photo-thermal nanomaterials.The average surface heat transfer coefficient of CNC is 7.0×105 W/(m2·K).Such excellent surface heat transfer performance attributes to the micro-nanoscale,the helical morphology and the unique thermal properties of CNC.Thus,CNCs are expected to be widely used in the fields of cancer photo-thermal therapy,micro/nano heat generators and heat exchangers.Thirdly,a single CNC,with both ends fixed,is used as a high-precision force sensor for the measurement of liquid surface tension coefficient by tearing-off method.The surface tension coefficients of deionized water and alcohol at room temperature are measured.The error between the experimental results and the standard values is less than 3.8%,which is superior to those from most traditional measurements.Conversely,the elastic coefficient of CNC is also measured accurately in situ by a standard liquid with known surface tension coefficient,with error of less than 3.2%.In addition,the tested liquid is directly measured by a standard liquid,with an error of less than 5.5%,without the necessity of knowing the geometric parameter and elastic constant of CNC.This study provides a theoretical and practical basis for the applications of CNCs in micro/nano-force sensor and microfluidics.Finally,with the help of the fluorescence resonance energy transfer(FRET)technique,an individual CNC is used as a flexible noninvasive probe for exploring the mechano and electro-sensitivity of a single living cell.It is found that CNCs have low cytotoxicity.A CNC probe is used to apply local mechanical stimulus for exploring the mechano-sensitivity of osteosarcoma cell.The stimulated cell shows spatial polarized FRET response in the first ten minutes.Then a CNC-based electrode exerts local electrical stimulus on a living cell.The FRET emission ratio of the activated cell shows notable spatial polarized response.The FRET ratio increases preferentially near the stimulated region,and then the ratio distribution become uniform gradually.After withdrawing the stimulus,the FRET ratio of the cells returns to the initial state.The physiological structures and functions are unaffected during the experimental process.Thus,CNC-based probe is a powerful tool for the investigations for intracellular mechanical and electrical transduction mechanism,cellular behaviors regulation and cellular electrical signal detection.