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Title: Diffractive encoding of microparticles for application to bead-based biological assays
Author: Birtwell, Sam William
ISNI:       0000 0001 3465 289X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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A new method for high-capacity encoding of microbeads that allows non-contact optical reading has been developed. In this new approach, a bead is encoded by a number of superimposed gratings with different periods manufactured on the surface of the bead, where each distinguishable tag has a unique combination of superimposed gratings. The tags are read optically at a distance, by detecting the diffraction pattern produced by the superimposed gratings. It has been demonstrated that the tagging method allows for millions of unique and distinguishable tags only a few tens of micrometers in size, when read by visible laser light. Using 2-dimensional superimposed gratings has been demonstrated to further increase the number of unique tags. The tagging method was first demonstrated using chromium-on-glass libraries of tags manufactured by e-beam lithography. Two libraries containing tags with up to five su- perimposed gratings were fabricated, one containing 1-dimensional tags, and the other containing 2-dimensional tags. A laser reading system has been developed including a software package that automatically identifies individual tags in the library. Capacity for up 68000 unique 50/iin long 1-dimensional tags and up to 108 unique 50 x 50/xm 2-dimensional tags was demonstrated. The diffractive tags were developed for biological, chemical and medical applications by manufacturing them from the polymer SU8, which is suitable for biochemical functionalisa- tion. A nano-imprint process for creating diffractive tags in SU8 has been developed, that allows for high-throughput manufacturing. A library of 100 different tags were shown to produce high-quality diffraction patterns, recognisable in the laser reading system. Capac- ity for up to 104 unique lOO^xm long 1-dimensional tags and up to 108 unique 100 x 100/LXHI 2-dimensional tags was demonstrated using this manufacturing method. A version of the tagging technology based on holographic writing has been developed. Holograms of binary arrays of spots were written into SU8 doped with a photochromic dye. This version of the technology offers a number of potential advantages, including use of error-checking algorithms and smaller diffraction angles. Capacity for 1014 codes was demonstrated to be theoretically achievable on a 100 x 100/i,m tag. A laser reading system has been developed with a software package that automatically identifies individual holographic tags. Capacity for 1019 tags was demonstrated on bulk photochromic-doped SU8. A dry-etch based method was developed for manufacturing individual particles of SU8 doped with photochromic dye. Capacity for 512 tags has been demonstrated on a 500/u,m particle. Additionally, it was shown that tags written using this technique could be erased and re-written, which is the first demonstration of rewritable microbead tagging.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available