Microparticle manipulation using CW and modulated diode laser

Qian, Yang (2018) Microparticle manipulation using CW and modulated diode laser. PhD thesis, University of Glasgow.

Abstract

Various platforms for microparticle manipulation have already been applied as useful tools for research in the life science field over recent decades. So far, several techniques have been investigated with their own advantages and limitations. For label-free approaches, such as acoustic tweezers, samples can be moved, controlled and separated in a gentle and precise manner. In order to achieve non-contact and remote control approaches, laser ultrasonics will be a potential technique for the acoustic tweezing field. In addition, using laser-induced thermal forces will be a novel and alternative tool for micromanipulation.

In this thesis, new platforms were developed for microparticle trapping and manipulation by either laser-induced surface acoustics based on a modulatable diode laser or laser-induced thermal forces without any absorbing coatings on the substrate.

For laser-induced surface acoustics, the intensity of generated surface acoustic waves (SAWs) based on our experimental setup was measured first. With inspiration from the literature, several attempts were made to generate and detect SAWs using a modulated laser beam from a diode laser by different combinations of generation methods and detection techniques, and improvements of the experimental system. However, none of the expected signals could be observed and measured. The factors that affected the amplitude of the SAWs were further investigated by numerical modelling. The results show that the surface displacement was enhanced significantly with a thin metal layer coated on the substrate, and by increasing the optical intensity within the illumination region at low modulation frequencies (~1 kHz). However, the displacement decreased greatly with frequency. At the high frequency (25 MHz) used in the experiments, it reduced to 2.95 fm, which was 5 orders of magnitude smaller than that at 1 kHz. It can be concluded that the generated SAWs were too weak to move particles under our experimental conditions.

Moreover, microparticles and biological samples were trapped and manipulated successfully in a thin fluidic chamber by the combined effect of laser-induced thermal forces. The characterisations of the physical phenomena were further studied by looking into the relations between particle speed and incident optical power and particle size. Furthermore, numerical modelling based on the experiments was undertaken to further explain the phenomena and investigate the underlying mechanisms. In summary, this new platform opens up the possibility to develop a novel micromanipulation technique with benefits of low cost, compact, biocompatible, modest optical power (≤ 200 mW) and being easy to set up and operate, which provides significant advantage over large system usually used for micromanipulation.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Laser ultrasonics, surface acoustic waves, SAW, optics, laser, microscopy, acoustics, ultrasounds, acoustic streaming, droplets, microfluidics, thermophoresis, thermal convection flow, microparticle manipulation, optical tweezing, thermal imaging, interdigital transducer.
• Subjects: Q Science > Q Science (General); Q Science > QC Physics; T Technology > T Technology (General); T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Supervisor's Name: Marsh, Prof. John and Neale, Dr. Steven
• Date of Award: 2018
• Depositing User: Dr Yang Qian
• Unique ID: glathesis:2018-40963
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 Jan 2019 16:15
• Last Modified: 28 Jan 2020 10:02
• URI: https://theses.gla.ac.uk/id/eprint/40963

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