Design and construction of optical tweezers for trapping single nano- and microparticles
(2026) PHYM03 20261Combustion Physics
Department of Physics
- Abstract
- Micro- and nanoscale pollutants dispersed at low concentrations in the environment pose increasing threats to human health and ecosystems. However, investigating the properties of individual particles remains challenging because conventional characterization methods mainly rely on ensemble measurements. Optical tweezers provide a promising approach for single-particle trapping and open new possibilities for their characterization. In this work, an optical tweezers setup was constructed and used to trap individual polystyrene (PS) beads and soot particles. Trapping experiments were performed on particles of various sizes under different laser powers, demonstrating the capability of the system to trap both particle types. Numerical analysis... (More)
- Micro- and nanoscale pollutants dispersed at low concentrations in the environment pose increasing threats to human health and ecosystems. However, investigating the properties of individual particles remains challenging because conventional characterization methods mainly rely on ensemble measurements. Optical tweezers provide a promising approach for single-particle trapping and open new possibilities for their characterization. In this work, an optical tweezers setup was constructed and used to trap individual polystyrene (PS) beads and soot particles. Trapping experiments were performed on particles of various sizes under different laser powers, demonstrating the capability of the system to trap both particle types. Numerical analysis was further employed to examine the dependence of trapping stability on particle size to enhance the understanding of optical tweezers. Additionally, by tracking and analyzing the Brownian motion of a single trapped PS particle, the system performance and its potential limitations were quantitatively discussed. For soot particles, experimental results also indicate that the trapping process is more complex compared to PS particles as they can exhibit behaviors such as rotation and aggregation. Therefore, additional considerations are required when trapping them. Possible underlying physical mechanisms are qualitatively discussed, providing a basis for future quantitative investigations. Finally, the possible improvements to address current system limitations are proposed, offering guidance for the eventual application of this setup to ex situ spectroscopic measurements of single particles. (Less)
- Popular Abstract
- Micro- and nanoparticles are widespread in the environment, originating from sources such as engines, industrial manufacturing, and combustion processes. These particles can strongly influence air quality, climate, and human health. However, studying them remains challenging especially when they are too small to be directly observed by the naked eye and are easily influenced by the environment.
Most traditional measurement techniques provide information about large groups of particles, while investigating particle behavior at smaller scales or studying individual particles directly remains challenging. To address this problem, an optical tweezers setup based on the Thorlabs Modular Optical Tweezers Kit was constructed using a green... (More) - Micro- and nanoparticles are widespread in the environment, originating from sources such as engines, industrial manufacturing, and combustion processes. These particles can strongly influence air quality, climate, and human health. However, studying them remains challenging especially when they are too small to be directly observed by the naked eye and are easily influenced by the environment.
Most traditional measurement techniques provide information about large groups of particles, while investigating particle behavior at smaller scales or studying individual particles directly remains challenging. To address this problem, an optical tweezers setup based on the Thorlabs Modular Optical Tweezers Kit was constructed using a green laser. Optical tweezers can use light to hold and manipulate small particles without touching them directly, which enables the particle to be isolated from the surrounding environment. The core contribution of this thesis is the design and construction of such a setup.
The setup was first tested using tiny plastic spheres of different sizes, which behaved in a stable and predictable way. Meanwhile, video microscopy was employed to track the geometric center of the particles, thereby further revealing the differences in the motion behavior between trapped particles and diffusing particles. After that, the setup was used to trap soot particles generated by a MiniCAST soot generator. Unlike the plastic spheres, soot particles were much more challenging to handle and exhibit some interesting behaviors. They undergo rotation and have a very short “survival” time, as they are easily damaged under the laser. These observations show that soot behaves very differently from ordinary particles and that optical tweezers have the potential to provide new insights into the behavior of soot at smaller and more controlled scales.
Overall, this work demonstrates the successful construction of a complete optical tweezer setup and shows that optical trapping can become a promising tool for single-particle soot research, with potential applications in environmental science, combustion studies, and atmospheric physics. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/student-papers/record/9232304
- author
- Zhao, Kun LU
- supervisor
- organization
- course
- PHYM03 20261
- year
- 2026
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Optical tweezers, Optical trapping, Soot particles, Brownian motion
- language
- English
- id
- 9232304
- date added to LUP
- 2026-06-09 10:08:12
- date last changed
- 2026-06-09 10:08:12
@misc{9232304,
abstract = {{Micro- and nanoscale pollutants dispersed at low concentrations in the environment pose increasing threats to human health and ecosystems. However, investigating the properties of individual particles remains challenging because conventional characterization methods mainly rely on ensemble measurements. Optical tweezers provide a promising approach for single-particle trapping and open new possibilities for their characterization. In this work, an optical tweezers setup was constructed and used to trap individual polystyrene (PS) beads and soot particles. Trapping experiments were performed on particles of various sizes under different laser powers, demonstrating the capability of the system to trap both particle types. Numerical analysis was further employed to examine the dependence of trapping stability on particle size to enhance the understanding of optical tweezers. Additionally, by tracking and analyzing the Brownian motion of a single trapped PS particle, the system performance and its potential limitations were quantitatively discussed. For soot particles, experimental results also indicate that the trapping process is more complex compared to PS particles as they can exhibit behaviors such as rotation and aggregation. Therefore, additional considerations are required when trapping them. Possible underlying physical mechanisms are qualitatively discussed, providing a basis for future quantitative investigations. Finally, the possible improvements to address current system limitations are proposed, offering guidance for the eventual application of this setup to ex situ spectroscopic measurements of single particles.}},
author = {{Zhao, Kun}},
language = {{eng}},
note = {{Student Paper}},
title = {{Design and construction of optical tweezers for trapping single nano- and microparticles}},
year = {{2026}},
}