Creating line defects with a single micro-sphere width in a DNA-linked 2D colloidal crystal array using a pulsed laser

A creation of micron-size narrow line defects in 2D colloidal crystal array was successfully accomplished using a focused pulsed laser. The 2D colloidal crystal arrays were obtained by a convective assembly of polystyrene latex micro-spheres (1.8 μm) and then immobilized onto the glass substrate by DNA hybridization process. To release a micro-sphere from the crystal, a focused laser beam was utilized to de-hybridize the DNA by raising the temperature above its melting point. From previous studies (Geiss E, Fabrication and defect design in two-dimensional colloidal photonic crystals. Ph.D dissertation thesis, 2003; Kim et al., Mater Sci Eng 26:1401–1407, 2006; Geiss et al., sudmitted), using a continuous argon ion laser, 514 nm, line-writing in colloidal crystal with 2–4 micro-sphere widths were achieved. In this study using the Nd:YAG pulsed laser’s second harmonic, 532 nm, line-writing of 1 micro-sphere width was accomplished. The presence of EB (ethidium bromide) dye that intercalates into the ds-DNA strands that bind the micro-spheres to the substrate facilitated the micro-sphere releasing process by reducing the laser energy required to release a micro-sphere. Factors that influenced controlled defect insertion were the medium containing the colloidal crystal, the dyes imposed on the crystal and the self-assembled micro-sphere groups. The most effective medium condition were determined at 1 mM global EB dye in 0.1 M NaCl for removing an individual micro-sphere in single micro-spheres, groups of micro-spheres and the close-packed arrays. Single micro-sphere width simple curves and corners in the photonic crystals were then created.