A Single-cell Manipulation Method Based On Photothermal Fiber Tweezers

Traditional cell analysis technologies often use the average data of multiple similar cells to represent the information of a single cell,which ignores the cell heterogeneity.Single-cell analysis technologies have developed rapidly and have great significance to technologies such as genomics and precision medicine,because they allow in-depth studies of individual cells at the single-cell level.The selective manipulation of single cells is very important for the sampling,sorting,assembly,and subsequent single cell analysis or detection of biological materials,so there is a need to develop effective single cell manipulation techniques without cell damage.So far,most of the existing single-cell manipulation systems have limitations like complex operations,high technical thresholds for equipment,small scope of application,damage to cells and so on.There are few methods available for single living cell manipulation in solution.This study proposes a new single-cell manipulation method that enables manipulation of single living cells in solution through reversable binding of functionalized surface and cell membrane,which has good biocompatibility and cellular versatility.The key design is a biocompatible photothermal fiber tweezer,whose three layer surface structure consists of nano photoprobe,gold nanofilm,and thermosensitive hydrogel,thiolated poly(Nisopropylacrylamide)(PNIPAM-SH).The biocompatible photothermal fiber tweezer is connected to the light source through the optical fiber,then fixed on a micromanipulator system to constitute a complete single-cell manipulation platform which displays excellent performance of good platform compatibility,low technical threshold,low energy consumption and fast response speed.The main research contents of this paper are as follows:(1)COMSOL simulation of photothermal fiber tweezers: The proposed core structure of a biocompatible photothermal fiber tweezer cleverly combines the surface plasmons mediated photothermal effect of the gold nanofilm with the thermally induced phase transition of the thermosensitive hydrogel.The photothermal fiber tweezer has been modeled and simulated using COMSOL Multiphysics software.The electromagnetic responses in frequency domain and thermal responses in time domain show good photothermal properties of photothermal fiber tweezers.When the input power is set to 900 μW,the maximum temperature of the system can reach 40.4 °C and there is an obvious reaction zone.The advantages of low power,strong locality,and fast response speed are very suitable for the single-cell manipulation method in this study.(2)Preparation and characterization of photothermal fiber tweezers: The biocompatible photothermal fiber tweezers have been prepared and characterized.The experimental results show that the actual photothermal effect has similar trends and characteristics with simulation results and that functionalized surface can achieve controllable cell adhesion.The photothermal effect and cell adhesion of the functionalized surface meet the design requirements of the singlecell manipulation method,and regulating the temperature change and the corresponding thermally induced phase transition can control the change in hydrophilicity and hydrophobicity of the functionalized surface,and further controlling the change in the adhesion between the surface and the target cells.(3)Study of the single-cell manipulation method: A suitable single-cell manipulation platform based on biocompatible photothermal fiber tweezers has been built and used to conduct several experiments using pluripotent stem cells,PC12 cells and human dermal fibroblasts,which confirm that the platform has diverse single-cell manipulation functions from selective capture and position-controlled release of target cell to 3-D pathway free transport and single cell isolation.In addition,the relationship between optical power and time of cell capture and release has been explored,and an input power as low as 900 μW can be used as the manipulating condition to realize single-cell capture within 20 s.The optical power required by our single cell manipulation method is much lower than the current common optical manipulation techniques.