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 infectionensure 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 crossgratings (SRCG) of unit cell size ranging from 8 x 8 m 2 (125 lines / mm) to as small as 1 x 1 m 2 (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 m 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.

Optical Response of PDMS Surface Diffraction Gratings under Exposure to Volatile Organic Compounds

“…AFM images of the remaining four gratings are shown in Figure S1 in the Supporting Information. For lower spatial frequencies (higher grating periods), the obtained surface depths were higher, which emerge from the properties of the photopolymer during holographic irradiation (a higher period of interference pattern enables the fabrication of deeper surface gratings). , Table summarizes the profile characteristics of the fabricated PDMS gratings and their theoretical diffraction efficiencies in the first and zeroth orders. Among them, two gratings with the same period of 8 μm but different depths were fabricated.…”

“…Master gratings with sinusoidal shapes, of which PDMS copies were prepared, had been fabricated holographically in acrylamide photopolymer following a previously described procedure. , Briefly, a photopolymer mixture containing Methylene Blue as a sensitizer was poured on microscopic glass slides and left steadily to dry for 6 h. Then, samples were irradiated with two 660 nm laser beams of a total intensity of 1.1 mW/cm 2 for 60 s (Cobolt Flamenco), creating an interference pattern consisting of dark and bright regions on the samples’ surface. Due to the polymerization-driven diffusion in the material, surface relief gratings were formed.…”

Thermal effects on the VOC-sensitive polydimethylsiloxane holographic gratings

“…Master gratings with sinusoidal shapes had been fabricated holographically in acrylamide photopolymer following a procedure described previously. 16,55,56 Poly(dimethylsiloxane) (PDMS) was prepared by thoroughly blending the elastomer base and curing agent in a ratio of 10:1. Next, the PDMS mixture was poured onto master gratings positioned within moulds and allowed to settle for 1 hour to ensure uniform infiltration into the surface profile of the grating.…”