研究目的
Investigating the importance of the surrounding fluid motion in optical trapping and revealing convection fluid dynamics forced by optical trapping with a focused laser beam.
研究成果
The study concludes that optical forces and resulting particle motion can induce large-scale fluid convection to accumulate target particles at the laser focal spot. The theoretical model, despite its simplicity, effectively predicts fluid flow induced by particle motion due to optical forces. To avoid fluid convection, using a dilute solution with small diameter particles is suggested.
研究不足
The study acknowledges the difficulty in controlling the number of particles N in situ due to sedimentation by gravity. The model simplifies the fluid-particle interaction, and the effect of particle concentration and diameter on flow speed is not fully explored. The comparison between experimental and numerical results is limited by the nonuniformity in the circumferential direction observed in experiments.
1：Experimental Design and Method Selection:
The study uses particle-image-velocimetry (PIV) analysis of fluorescent particles in solutions to evaluate fluid flow in optical trapping. A theoretical model based on numerical analysis of Navier?Stokes equations with the Boussinesq approximation is developed to consider temperature elevation induced by a photothermal effect and the effect of particle motion on fluid flow.
2：Sample Selection and Data Sources:
Fluorescent dye-doped polystyrene particles with diameters of 1 μm and 500 nm are used as samples. These particles are diluted in distilled water to specific concentrations.
3：List of Experimental Equipment and Materials:
Equipment includes a cw Nd:YVO4 laser for optical trapping, an inverted optical microscope, objective lens, He?Ne laser for alignment, xy scanning stage, piezo-actuator for z-position control, mercury lamp for excitation, sCMOS camera for fluorescence image capture, and PIV analysis software.
4：Experimental Procedures and Operational Workflow:
The laser power is tuned and focused through the objective lens onto the sample. Fluorescence images are captured to analyze particle motion and fluid flow. The PIV analysis is performed to evaluate the flow dynamics.
5：Data Analysis Methods:
The PIV analysis provides flow vectors and magnitudes. Numerical simulations are conducted to compare with experimental results, focusing on the effects of thermal convection and particle motion on fluid flow.
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Objective lens
UPlanFLN
Olympus
Used for tightly focusing the laser beam
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xy scanning stage
BIOS-105
Sigma-koki
Used for mounting and positioning the sample
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Piezo-actuator
P-721 PIFOC
Physik Instrumente
Used for controlling the z-position of the objective
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sCMOS camera
Zyla4.2plus
Andor
Used for capturing fluorescence images
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FluoSpheres carboxylate-modified microspheres
F8820
Thermo Fisher Scientific
Used as sample suspension for optical trapping experiments
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FluoSpheres carboxylate-modified microspheres
F8812
Thermo Fisher Scientific
Used as sample suspension for optical trapping experiments
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Inverted optical microscope
IX-71
Olympus
Used for focusing the laser beam and observing the sample
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Nd:YVO4 laser
BL-106C
Spectra Physics
Used for optical trapping
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He?Ne laser
1137P
JDS Uniphase
Used for the alignment of Nd:YVO4 laser beam
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PIV analysis software
Flownizer 2D
Ditect Co. Ltd.
Used for analyzing the fluid motion
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