Experimental study of the characteristics of novel microactuator based on optothermal expansion

A novel asymmetric optothermal microactuator was developed. A microactuator of 750μm length was machined by an excimer laser micmmachining system using single layer material. It had an asymmetric structure consisting of two thin expansion arms with different widths. A laser diode （660nm） was employed as the external power source to activate the microactuator. We introduced a charge coupled device （CCD）-combined optical microscope and a computer system to observe and capture the microactuator＇ s deflection and vibration. Experiments have been carried out to check the feasibility of deflection, and the data of deflection have been measured under different laser power as well as under different pulse frequency. The results show that the actuator can practically generate an obvious lateral deflection or vibration, the maximum could be larger than 20μm. Moreover, the deflection status of the microactuator could be controlled wirelessly or remotely by changing the laser power and its pulse frequency.

Low-temperature optothermal nanotweezers

Optical tweezers that rely on laser irradiation to capture and manipulate nanoparticles have provided powerful tools for biological and biochemistry studies.However,the existence of optical diffraction-limit and the thermal damage caused by high laser power hinder the wider application of optical tweezers in the biological field.For the past decade,the emergence of optothermal tweezers has solved the above problems to a certain extent,while the auxiliary agents used in optothermal tweezers still limit their biocompatibility.Here,we report a kind of nanotweezers based on the sign transformation of the thermophoresis coefficient of colloidal particles in low-temperature environment.Using a self-made microfluidic refrigerator to reduce the ambient temperature to around 0℃in the microfluidic cell,we can control a single nanoparticle at lower laser power without adding additional agent solute in the solution.This novel optical tweezering scheme has provided a new path for the manipulation of inorganic nanoparticles as well as biological particles.

Atomistic modeling and rational design of optothermal tweezers for targeted applications

Optical manipulation of micro/nanoscale objects is of importance in life sciences,colloidal science,and nanotechnology.Optothermal tweezers exhibit superior manipulation capability at low optical intensity.However,our implicit understanding of the working mechanism has limited the further applications and innovations of optothermal tweezers.Herein,we present an atomistic view of opto-thermo-electro-mechanic coupling in optothermal tweezers,which enables us to rationally design the tweezers for optimum performance in targeted applications.Specifically,we have revealed that the non-uniform temperature distribution induces water polarization and charge separation,which creates the thermoelectric field dominating the optothermal trapping.We further design experiments to systematically verify our atomistic simulations.Guided by our new model,we develop new types of optothermal tweezers of high performance using low-concentrated electrolytes.Moreover,we demonstrate the use of new tweezers in opto-thermophoretic separation of colloidal particles of the same size based on the difference in their surface charge,which has been challenging for conventional optical tweezers.With the atomistic understanding that enables the performance optimization and function expansion,optothermal tweezers will further their impacts.

Advances in inorganic nanoparticles trapping stiffness measurement:A promising tool for energy and environmental study

Optical tweezers system has emerged as an efficient tool to manipulate tiny particles in a non-invasive way.Trapping stiffness,as an essential parameter of an optical potential well,represents the trapping stability.Additionally,trapping inorganic nanoparticles such as metallic nanoparticles or other functionalized inorganic nanoparticles is important due to their properties of good stability,high conductivity,tolerable toxicity,etc.,which makes it an ideal detection strategy for bio-sensing,force calculation,and determination of particle and environmental properties.However,the trapping stiffness measurement(TSM)methods of inorganic nanoparticles have rarely been analyzed and summarized.Here,in this review,the principle and methods of TSM are analyzed.We also systematically summarize the progress in acquiring inorganic particles trapping stiffness and its promising applications.In addition,we provide prospects of the energy and environment applications of optical tweezering technique and TSM.Finally,the challenges and future directions of achieving the nanoparticles trapping stiffness are discussed.