Propulsion of polymer particles on caesium ion-exchanged channel waveguides for stem cell sorting applications

Abstract

Optical trapping of particles has become a powerful non-mechanical and nondestructive technique for precise particle positioning. The manipulation of particles in the evanescent field of a channel waveguide potentially allows for sorting and trapping of several particles and cells simultaneously. In the evanescent field above an optical channel waveguide, particles experience three optical forces; i) a transverse gradient force, which acts in the direction of the intensity gradient, ii) a scattering force, which acts in the direction of the wave propagation and is proportional to the surface intensity and, iii) an absorption force, which is dependent upon the complex refractive index of the particle. A particle in the evanescent field will be propelled and trapped with a dependence on the intensity gradient (a property dependent upon the physical characteristic of the waveguide). A channel waveguide producing such an evanescent field can be photolithographically defined on a glass substrate and thus has the potential to be integrated into a single chip device.

This thesis describes the studies carried out, both theoretically and experimentally, to establish optimum waveguide fabrication conditions and the experimental requirements to ultimately allow for the separation of polymer particles and mammalian cells according to their size and refractive index. Theoretical aspects of the interaction of particles and cells on surfaces were evaluated and their Brownian motion was investigated. Optical channel waveguides of different characteristics have been fabricated using caesium ion-exchange process on soda-lime substrates. The propulsion of polymer particles has been achieved and characterised against different optical parameters, waveguide conditions and particle’s characteristics on different surfaces. The propulsion of lymphoblastoma cells was demonstrated and the trapping of teratocarcinoma cells was evaluated. These results provide evidence for the potential application of the system for trapping and sorting stem cells.

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ORCID for James Wilkinson: orcid.org/0000-0003-4712-1697

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