Fabrication and characterisation of large area, uniform, and controllable surface relief patterns in photopolymer material

Abstract

As the risk of antibiotic resistant pathogens increases, development of convenient point of care devices is essential. Such devices would help avoid infection – ensure cleanliness of environments and assist in bacteria analysis. The ultimate aim of the research presented here is to develop a compact, cost effective, easy to use optical device which is capable of detecting and quantifying bacteria in an aqueous sample. The surface relief patterns have a dual role, they provide a diffracted light signal, and control the adhesion of the bacteria to the surface. The strength of the diffracted signal is expected to provide a quantitative measure of the number of bacterial cells attached to the patterned surface. An adjustable holographic set up for controlled patterning of a photopolymer surface using three-beams of varying intensity, incident angles, and state of polarisation was built. The system allows for the creation of surface relief cross-gratings (SRCG) of unit cell size ranging from 8 x 8 μm² (125 lines / mm) to as small as 1 x 1 μm² (1000 lines/ mm). The surfaces are analysed via AFM, Phase contrast Microscopy, Fast Fourier transform analysis of the collected images and diffraction efficiency measurements. The surface relief amplitude dependence on recording parameters is investigated, the results demonstrate a strong dependence of the surface relief height on the period of the recorded structures. The largest surface relief amplitude achieved is 300 nm at 8 μm period. The possibility to achieve control over surface roughness by optical patterning was experimentally confirmed. The production and characterisation of large area uniform SRCG, with controllable patterns will allow further experiments aiming at the development of bacterial assays to be completed, namely SRCG contact copying in water resistant materials and their functionalisation by coating.